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The Geologic Time Scale is a system used by scientists to describe the timing and relationships between events in Earth’s history. It covers a vast expanse of time, from the formation of the planet nearly 4.6 billion years ago to the present day.

One of the key concepts of the Geologic Time Scale is the division of time into units of varying lengths. The largest unit is the eon, which is further divided into smaller units such as eras, periods, and epochs.

The first eon, the Hadean, lasted from the formation of the Earth until about 4 billion years ago. It was a time of intense volcanic activity and frequent meteor impacts, and it is thought that the first oceans formed during this eon.

The next eon, the Archean, lasted from 4 to 2.5 billion years ago. This was a time of early life on Earth, and the first microorganisms appeared during this eon.

The third eon, the Proterozoic, lasted from 2.5 billion to 541 million years ago. This was a time of the evolution of early life forms and the formation of the first continents.

The Phanerozoic eon, which began 541 million years ago and continues to the present day, is characterized by the evolution of multicellular life forms and the development of the first animals. This eon is divided into three eras: the Paleozoic, the Mesozoic, and the Cenozoic.

The Paleozoic era, from 541 to 252 million years ago, saw the rise of the first fish and the first land plants. It was also a time of great diversification, as new groups of animals evolved and formed complex ecosystems.

The Mesozoic era, from 252 to 66 million years ago, is best known for the dinosaurs. This era also saw the evolution of birds and the first mammals.

The Cenozoic era, from 66 million years ago to the present day, saw the evolution of modern mammals and the rise of humans.

The Geologic Time Scale provides a framework for understanding the history of the Earth and the development of life on our planet. It is an important tool for geologists, paleontologists, and other scientists, who use it to study the rocks , fossils , and other evidence of Earth’s past and to understand how the planet has changed over time.

Development and evolution of the Geologic Time Scale

Divisions of time in the geologic time scale, key events in earth’s history and their placement in the geologic time scale, applications of the geologic time scale, limitations and criticisms of the geologic time scale, geologic time and the geologic column, quaternary period, neogene period, paleogene period, cretaceous period, jurassic period, triassic period, permian period, pennsylvanian period, mississippian period , devonian period, silurian period, ordovician period, cambrian period, proterozoic eon, archean eon.

The Geologic Time Scale is a fundamental tool used by geologists and other Earth scientists to understand and describe the history of our planet. It is a system for organizing the history of the Earth into units of time, from the smallest to the largest, based on the events and processes that have occurred. In this article, we will explore the development and evolution of the Geologic Time Scale, and how it has become an indispensable tool for scientists.

The history of the Geologic Time Scale can be traced back to the late 17th century, when a Danish scientist named Nicolas Steno proposed that rock strata were formed by the accumulation of sediments over time. This idea formed the basis for the concept of stratigraphy , which is the study of the sequence of rock strata and the events they record.

In the following centuries, other scientists made important contributions to the development of the Geologic Time Scale. For example, in the 18th and 19th centuries, geologists such as William Smith and Charles Lyell recognized the importance of fossils in understanding the history of the Earth. They used the distributions of fossils in rock strata to construct the first rough outlines of the Geologic Time Scale.

One of the major breakthroughs in the development of the Geologic Time Scale came in the early 20th century, with the discovery of radioactivity. Scientists realized that they could use the decay of radioactive isotopes in rocks to determine the ages of rocks and strata, and this provided a much more precise way of determining the ages of the Earth and its various rock formations.

Since then, the Geologic Time Scale has continued to evolve and be refined. Today, it is a sophisticated tool that is used by geologists and other Earth scientists to study the history of the planet and the evolution of life on Earth. The Geologic Time Scale is divided into several large units of time, including eons, eras, periods, and epochs, and it provides a framework for understanding the relationships between events in Earth’s history.

In conclusion, the development and evolution of the Geologic Time Scale has been a slow and ongoing process, spanning several centuries and involving contributions from many scientists. Today, it is a critical tool for understanding the history of our planet, and it continues to be refined as new data and techniques become available.

The Geologic Time Scale is a system for organizing the history of the Earth into units of time, from the smallest to the largest, based on the events and processes that have occurred. Understanding the divisions of time in the Geologic Time Scale is crucial for comprehending the history of our planet and the evolution of life on Earth.

The Geologic Time Scale is divided into several large units of time, including eons, eras, periods, and epochs. The largest unit of time is the eon, which is divided into eras. Eras are further divided into periods, and periods are divided into epochs. Each unit of time is defined by specific events and changes that took place on Earth, such as the formation of the planet, the evolution of life, and mass extinctions.

The two eons in the Geologic Time Scale are the Precambrian eon and the Phanerozoic eon. The Precambrian eon covers the first four billion years of Earth’s history and is divided into three eras: the Hadean, Archean, and Proterozoic. The Hadean era, named after the Greek word for “hell,” was a time of intense heat and volcanic activity, and it is thought to have lasted from 4.6 billion to 4 billion years ago. The Archean era saw the formation of the first continents and the evolution of the first simple life forms, and it lasted from 4 billion to 2.5 billion years ago. The Proterozoic era saw the evolution of more complex life forms and the formation of the first multicellular organisms, and it lasted from 2.5 billion to 541 million years ago.

The Phanerozoic eon, which began 541 million years ago, is the eon during which life has been visible and abundant on Earth. It is divided into three eras: the Paleozoic, Mesozoic, and Cenozoic. The Paleozoic era, which lasted from 541 million to 252 million years ago, saw the evolution of the first fishes, amphibians, reptiles, and dinosaurs, as well as the formation of the first forests and the first mass extinctions. The Mesozoic era, which lasted from 252 million to 66 million years ago, saw the evolution of the first birds and mammals and the reign of the dinosaurs, as well as the formation of the continents as we know them today and the extinction of the dinosaurs. The Cenozoic era, which began 66 million years ago and continues to the present day, has seen the evolution of humans and the development of modern ecosystems.

In conclusion, the divisions of time in the Geologic Time Scale provide a framework for understanding the history of the Earth and the evolution of life on our planet. From the smallest unit of time, the epoch, to the largest unit, the eon, each division is defined by specific events and changes that took place on Earth. Understanding the divisions of time in the Geologic Time Scale is an important step in comprehending the complex history of our planet.

One of the earliest key events in Earth’s history was the formation of the planet itself, which is estimated to have taken place approximately 4.6 billion years ago. This event marked the beginning of the Hadean era in the Precambrian eon and was followed by the evolution of the first simple life forms in the Archean era, which lasted from 4 billion to 2.5 billion years ago.

Another important event in Earth’s history was the evolution of the first multicellular organisms in the Proterozoic era, which lasted from 2.5 billion to 541 million years ago. This era also saw the first mass extinctions and the formation of the first continents.

The Phanerozoic eon, which began 541 million years ago, is the eon during which life has been visible and abundant on Earth. The Paleozoic era, which lasted from 541 million to 252 million years ago, saw the evolution of the first fishes, amphibians, reptiles, and dinosaurs, as well as the formation of the first forests and the first mass extinctions. The Mesozoic era, which lasted from 252 million to 66 million years ago, saw the evolution of the first birds and mammals and the reign of the dinosaurs, as well as the formation of the continents as we know them today and the extinction of the dinosaurs.

The Cenozoic era, which began 66 million years ago and continues to the present day, has seen the evolution of humans and the development of modern ecosystems. Key events in this era include the evolution of early primates, the development of Homo sapiens, and the emergence of human civilizations.

In conclusion, the Geologic Time Scale provides a framework for understanding the key events in Earth’s history and their placement in a chronological context. From the formation of the planet to the evolution of humans and the development of modern civilizations, the Geologic Time Scale helps to illustrate the relationships between these events and to place them in a historical context. Understanding the Geologic Time Scale is an important step in comprehending the complex history of our planet.

The Geologic Time Scale is a crucial tool for understanding the history of the Earth and the evolution of life on our planet. It has a wide range of applications in various fields, including geology, paleontology , biology, archaeology, and more. Some of the most important applications of the Geologic Time Scale are:

Age Dating of Rocks and Fossils : The Geologic Time Scale is used to determine the age of rocks , fossils, and other geological formations. This is essential for understanding the evolution of life on Earth and for reconstructing past environments and ecosystems.
Correlation of Rock Strata : The Geologic Time Scale is used to correlate rock strata across different geographic regions. This allows geologists to reconstruct the Earth’s history and to understand the relationships between different geological events.
Resource Exploration : The Geologic Time Scale is used by the petroleum , mineral, and mining industries to explore and extract natural resources . A knowledge of the age and depositional environment of rocks can be used to identify potential resource-rich areas.
Climate Change Studies : The Geologic Time Scale is used to study climate change over long periods of time. By analyzing rocks, fossils, and other geological formations, scientists can reconstruct past climate conditions and understand the mechanisms and causes of climate change.
Evolutionary Biology : The Geologic Time Scale is used by evolutionary biologists to understand the evolution of life on Earth. It provides a framework for understanding the relationships between different species and for reconstructing the evolutionary history of different groups of organisms.
Archaeology : The Geologic Time Scale is used by archaeologists to date archaeological sites and artifacts. This is essential for understanding the development of human civilizations and for reconstructing past cultural and technological systems.

In conclusion, the Geologic Time Scale is a versatile and indispensable tool for a wide range of scientific and practical applications. Its importance in understanding the history of the Earth and the evolution of life cannot be overstated, and it continues to play a critical role in shaping our understanding of the world we live in.

While the Geologic Time Scale is a crucial tool for understanding the history of the Earth and the evolution of life, it is not without limitations and criticisms. Some of the most important limitations and criticisms are:

Incomplete Fossil Record : The Geologic Time Scale is based on the fossil record, but the fossil record is inherently incomplete. Many species and geological events are not represented in the fossil record, and this can make it difficult to accurately reconstruct the Earth’s history.
Assumptions About Rates of Change : The Geologic Time Scale is based on assumptions about the rates of change of geological and biological processes. These assumptions can be challenged and revised as new data becomes available, leading to changes in the timing of events in the Geologic Time Scale.
Dating Techniques : The accuracy of the Geologic Time Scale is dependent on the accuracy of the dating techniques used to determine the ages of rocks, fossils, and other geological formations. Some dating techniques are more accurate than others, and the accuracy of different techniques can be affected by various factors such as contamination or the presence of isotopic anomalies.
Conflicting Interpretations : Different scientists can have conflicting interpretations of the same data, leading to different models of the Geologic Time Scale. This can result in disagreements about the timing of events and the relationships between different species and geological formations.
Controversies : The Geologic Time Scale is not immune to controversies, and different interpretations of data can lead to debates and disagreements about the history of the Earth and the evolution of life. For example, there have been controversies surrounding the timing of mass extinctions and the origins of different groups of organisms.

In conclusion, while the Geologic Time Scale is a powerful tool for understanding the history of the Earth and the evolution of life, it is not without limitations and criticisms. It is important to be aware of these limitations and to continually revise and refine our understanding of the Geologic Time Scale in light of new data and advances in scientific knowledge.

The Geologic Time Scale and the Geologic Column are related concepts in geology. The Geologic Time Scale is a standardized system for organizing the history of the Earth into specific time intervals, based on the ages of rocks, fossils, and other geological formations. The Geologic Column, on the other hand, is a representation of the vertical sequence of rock layers that make up the Earth’s crust.

The Geologic Column is an idealized representation of the rock layers that can be found at a single location. It is based on the principle of superposition, which states that younger rock layers are deposited on top of older rock layers. The Geologic Column can be used to illustrate the relative ages of rocks and the sequences of geological events that have taken place at a particular location.

The Geologic Column can also be used in conjunction with the Geologic Time Scale to understand the relationships between different rock layers and the ages of different geological formations. By comparing the rock layers found at a particular location with the standard Geologic Column, geologists can determine the relative ages of different rock layers and the sequences of geological events that have taken place.

In conclusion, the Geologic Time Scale and the Geologic Column are related concepts in geology that are used to understand the history of the Earth and the evolution of life. The Geologic Time Scale is a standardized system for organizing the history of the Earth into specific time intervals, while the Geologic Column is a representation of the vertical sequence of rock layers that make up the Earth’s crust. By using these two concepts in combination, geologists can gain a deeper understanding of the history of the Earth and the evolution of life.

The Quaternary Period is the youngest and most recent period of the Cenozoic Era, which covers the last 2.6 million years of Earth’s history. The Quaternary Period is characterized by significant changes in the Earth’s climate, as well as the evolution and dispersal of modern human civilizations.

One of the defining features of the Quaternary Period is the presence of multiple ice ages, during which large portions of the Earth’s surface were covered in ice. During the ice ages, the Earth’s climate was much colder than it is today, and sea levels were much lower. These changes had a significant impact on the distribution of plants and animals, as well as the evolution of human civilizations.

Another key event of the Quaternary Period was the evolution of modern human species, such as Homo sapiens, and their dispersal across the Earth. During this time, human populations developed sophisticated technologies and societies, and they began to have a significant impact on the natural world.

In conclusion, the Quaternary Period is a critical time interval in the history of the Earth, characterized by significant changes in climate, the evolution of modern human species, and the development of human civilizations. By studying the Quaternary Period, we can gain a deeper understanding of the history of the Earth and the evolution of life, and we can also learn about the impact that humans have had on the natural world.

The Neogene Period is a division of the Cenozoic Era and covers the last 23 million years of Earth’s history. It follows the Paleogene Period and is divided into two subperiods: the Miocene and the Pliocene.

The Neogene Period is characterized by significant changes in the Earth’s climate, as well as the evolution and dispersal of many modern plant and animal species. During this time, the Earth’s climate became increasingly warmer, and the continents began to take on their present-day positions. This led to the development of new ecosystems and the evolution of many new species of plants and animals.

One of the most notable events of the Neogene Period was the evolution of modern mammals, including primates, whales, and elephants. The evolution of these mammals was driven by changes in the Earth’s climate and the formation of new ecosystems.

In conclusion, the Neogene Period is a critical time interval in the history of the Earth, characterized by significant changes in climate, the evolution of modern mammals, and the development of new ecosystems. By studying the Neogene Period, we can gain a deeper understanding of the history of the Earth and the evolution of life, and we can also learn about the interplay between environmental change and the evolution of species.

The Paleogene Period is a division of the Cenozoic Era and covers the time interval between 66 and 23 million years ago. It follows the Late Cretaceous Period and is divided into three subperiods: the Paleocene, Eocene, and Oligocene.

The Paleogene Period is characterized by significant changes in the Earth’s climate, as well as the evolution and extinction of many species of plants and animals. This period saw the aftermath of the mass extinction that wiped out the dinosaurs at the end of the Cretaceous, allowing for the evolution and diversification of mammals.

One of the defining events of the Paleogene Period was the evolution of modern mammals, including primates, rodents, and carnivores. These mammals took advantage of the new opportunities created by the extinction of the dinosaurs and quickly diversified into a wide range of new species.

In addition, the Paleogene Period saw the continued breakup of the supercontinent Pangea and the formation of the Atlantic Ocean. This had a significant impact on the Earth’s climate and led to the development of new ecosystems and the evolution of new species.

In conclusion, the Paleogene Period is a critical time interval in the history of the Earth, characterized by significant changes in climate, the evolution of modern mammals, and the aftermath of the mass extinction at the end of the Cretaceous. By studying the Paleogene Period, we can gain a deeper understanding of the history of the Earth and the evolution of life, and we can also learn about the interplay between environmental change and the evolution of species.

The Cretaceous Period is a division of the Mesozoic Era and covers the time interval between 145 and 66 million years ago. It follows the Jurassic Period and is divided into two subperiods: the Early Cretaceous and the Late Cretaceous.

The Cretaceous Period is known for several defining events, including the continued breakup of the supercontinent Pangea, the formation of the Atlantic Ocean, and the evolution of modern plants and animals. During this time, the Earth’s climate was warm and tropical, with high levels of atmospheric carbon dioxide, and the oceans were home to a diverse array of life, including ammonites , belemnites, and plesiosaurs.

One of the most notable events of the Cretaceous Period was the evolution of the dinosaurs, which became the dominant group of land-dwelling reptiles. Dinosaurs were highly diverse and ranged in size from small, feathered birds to massive herbivores and carnivores, such as Tyrannosaurus rex and Triceratops.

The Cretaceous Period also saw the evolution of the first flowering plants, which quickly diversified and became the dominant form of vegetation on land. The evolution of these plants had a significant impact on the Earth’s ecosystems and led to the development of new habitats for animals.

In conclusion, the Cretaceous Period is a critical time interval in the history of the Earth, characterized by significant changes in climate, the evolution of dinosaurs and flowering plants, and the continued breakup of Pangea. By studying the Cretaceous Period, we can gain a deeper understanding of the history of the Earth and the evolution of life, and we can also learn about the interplay between environmental change and the evolution of species.

The Jurassic Period is a division of the Mesozoic Era and covers the time interval between 201 and 145 million years ago. It follows the Triassic Period and is divided into two subperiods: the Early Jurassic and the Late Jurassic.

The Jurassic Period is known for several defining events, including the continued breakup of the supercontinent Pangea and the evolution of modern plants and animals. During this time, the Earth’s climate was warm and tropical, with high levels of atmospheric carbon dioxide, and the oceans were home to a diverse array of life, including ammonites, belemnites, and ichthyosaurs.

One of the most notable events of the Jurassic Period was the evolution of the dinosaurs, which became the dominant group of land-dwelling reptiles. Dinosaurs were highly diverse and ranged in size from small, feathered birds to large herbivores and carnivores, such as Stegosaurus and Allosaurus.

The Jurassic Period also saw the evolution of the first birds, which were closely related to dinosaurs and evolved from small, feathered theropod dinosaurs. The evolution of these early birds had a significant impact on the Earth’s ecosystems and led to the development of new habitats for animals.

In conclusion, the Jurassic Period is a critical time interval in the history of the Earth, characterized by significant changes in climate, the evolution of dinosaurs and birds, and the continued breakup of Pangea. By studying the Jurassic Period, we can gain a deeper understanding of the history of the Earth and the evolution of life, and we can also learn about the interplay between environmental change and the evolution of species.

The Triassic Period is a division of the Mesozoic Era and covers the time interval between 252 and 201 million years ago. It follows the Permian Period and is divided into two subperiods: the Early Triassic and the Late Triassic.

The Triassic Period is known for several defining events, including the formation of the supercontinent Pangea and the recovery of life following the Permian-Triassic mass extinction event, which wiped out more than 90% of marine species and 70% of terrestrial species. During this time, the Earth’s climate was warm and arid, with high levels of atmospheric carbon dioxide, and the oceans were home to a diverse array of life, including ammonites, ichthyosaurs, and placodonts.

One of the most notable events of the Triassic Period was the evolution of the dinosaurs, which became the dominant group of land-dwelling reptiles. Dinosaurs were highly diverse and ranged in size from small, agile predators to large herbivores, such as Plateosaurus.

The Triassic Period also saw the evolution of the first mammals, which were small, nocturnal, and insect-eating. The evolution of these early mammals had a significant impact on the Earth’s ecosystems and led to the development of new habitats for animals.

In conclusion, the Triassic Period is a critical time interval in the history of the Earth, characterized by significant changes in climate, the formation of Pangea, the recovery of life following the mass extinction event, and the evolution of dinosaurs and mammals. By studying the Triassic Period, we can gain a deeper understanding of the history of the Earth and the evolution of life, and we can also learn about the interplay between environmental change and the evolution of species.

The Permian Period is a division of the Paleozoic Era and covers the time interval between 298 and 252 million years ago. It follows the Carboniferous Period and is divided into two subperiods: the Early Permian and the Late Permian.

The Permian Period is known for several defining events, including the formation of the supercontinent Pangea and the largest mass extinction event in Earth’s history, the Permian-Triassic mass extinction event. During this time, the Earth’s climate was warm and arid, with high levels of atmospheric carbon dioxide, and the oceans were home to a diverse array of life, including ammonites, brachiopods , and reef-building organisms.

One of the most notable events of the Permian Period was the evolution of the first reptiles, which became the dominant group of land-dwelling vertebrates. Reptiles were highly diverse and ranged in size from small, insect-eating animals to large, herbivorous reptiles, such as Dimetrodon.

The Permian Period also saw the decline of the dominant group of marine animals, the trilobites , which were replaced by new groups of animals, such as ammonites and brachiopods.

In conclusion, the Permian Period is a critical time interval in the history of the Earth, characterized by significant changes in climate, the formation of Pangea, and the largest mass extinction event in Earth’s history. By studying the Permian Period, we can gain a deeper understanding of the history of the Earth and the evolution of life, and we can also learn about the interplay between environmental change and the evolution of species.

The Pennsylvanian Period is a division of the Carboniferous Period and covers the time interval between 323 and 298 million years ago. It follows the Mississippian Period and is characterized by the growth of abundant vegetation on land, including the first trees, which changed the Earth’s ecosystems and provided habitats for new groups of animals.

During the Pennsylvanian Period, the Earth’s climate was warm and moist, with high levels of atmospheric oxygen, and the oceans were home to a diverse array of life, including brachiopods, crinoids, and coral reefs.

One of the most notable events of the Pennsylvanian Period was the evolution of the first amphibians, which were well-adapted to life on land and in water. Amphibians were highly diverse and ranged in size from small, agile predators to large, herbivorous animals, such as Eryops.

The Pennsylvanian Period also saw the evolution of the first reptiles, which were small, terrestrial animals that were well-adapted to life on land. These early reptiles eventually gave rise to the dinosaurs and other groups of reptiles that dominated the Earth’s ecosystems during the Mesozoic Era.

In conclusion, the Pennsylvanian Period is a critical time interval in the history of the Earth, characterized by significant changes in the Earth’s ecosystems, the growth of vegetation on land, and the evolution of amphibians and reptiles. By studying the Pennsylvanian Period, we can gain a deeper understanding of the history of the Earth and the evolution of life, and we can also learn about the interplay between environmental change and the evolution of species.

The Mississippian Period is a division of the Carboniferous Period and covers the time interval between 359 and 323 million years ago. It follows the Devonian Period and precedes the Pennsylvanian Period.

The Mississippian Period is characterized by the growth of abundant vegetation on land, including the first large trees, which changed the Earth’s ecosystems and provided habitats for new groups of animals. During this time, the Earth’s climate was warm and moist, with high levels of atmospheric oxygen, and the oceans were home to a diverse array of life, including brachiopods, crinoids, and coral reefs.

One of the most notable events of the Mississippian Period was the evolution of the first land-dwelling vertebrates, such as the tetrapods. Tetrapods were the first four-limbed vertebrates and were well-adapted to life on land, where they could breathe air and escape predators.

The Mississippian Period also saw the formation of the first extensive coal-forming swamps, which produced coal that would become an important energy source for humans in later periods.

In conclusion, the Mississippian Period is a critical time interval in the history of the Earth, characterized by significant changes in the Earth’s ecosystems, the growth of vegetation on land, and the evolution of the first land-dwelling vertebrates. By studying the Mississippian Period, we can gain a deeper understanding of the history of the Earth and the evolution of life, and we can also learn about the interplay between environmental change and the evolution of species.

The Devonian Period is a division of the Paleozoic Era and covers the time interval between 419 and 359 million years ago. It follows the Silurian Period and precedes the Mississippian Period.

The Devonian Period is characterized by several important events in the evolution of life on Earth. It was during this time that the first jawed fish evolved, which were a major step in the evolution of vertebrates. The first tetrapods, or four-limbed vertebrates, also appeared during the Devonian Period.

The Devonian Period is also known as the “Age of Fishes” because of the incredible diversity of fish that evolved during this time, including the first sharks, bony fish, and lobe-finned fish. This diversity of fish helped to establish the oceans as the dominant habitat for life on Earth.

In addition to the evolution of fish, the Devonian Period was also marked by significant changes on land. For the first time, plants evolved that could survive out of water, including the first ferns, mosses, and liverworts. This paved the way for the evolution of the first land-dwelling animals, including arthropods and the first tetrapods.

In conclusion, the Devonian Period is a critical time interval in the history of the Earth, characterized by significant changes in the evolution of life on Earth, including the evolution of jawed fish, tetrapods, and the first land-dwelling plants. By studying the Devonian Period, we can gain a deeper understanding of the history of the Earth and the evolution of life, and we can also learn about the interplay between environmental change and the evolution of species.

The Silurian Period is a division of the Paleozoic Era and covers the time interval between 443 and 419 million years ago. It follows the Ordovician Period and precedes the Devonian Period.

The Silurian Period was a time of significant change and diversification in the evolution of life on Earth. During this time, the first vascular plants evolved, which allowed for the colonization of land by plants for the first time. This was a major milestone in the evolution of life on Earth and paved the way for the evolution of land-dwelling animals in later periods.

The oceans of the Silurian Period were also home to a diverse array of life, including the first armored fish, which were well-adapted to life in the ancient oceans. This period also saw the evolution of the first crinoids and brachiopods, which were important components of the ancient ocean ecosystems.

In conclusion, the Silurian Period is a critical time interval in the history of the Earth, characterized by significant changes and diversification in the evolution of life on Earth, including the evolution of the first vascular plants and armored fish. By studying the Silurian Period, we can gain a deeper understanding of the history of the Earth and the evolution of life, and we can also learn about the interplay between environmental change and the evolution of species.

The Ordovician Period is a division of the Paleozoic Era and covers the time interval between 485 and 443 million years ago. It follows the Cambrian Period and precedes the Silurian Period.

The Ordovician Period was a time of significant change and diversification in the evolution of life on Earth. During this time, the first jawless fish and primitive jawed fish evolved, which were important steps in the evolution of vertebrates. This period also saw the evolution of the first invertebrates with hard shells, such as trilobites, which dominated the oceans.

In addition to the evolution of early fish and invertebrates, the Ordovician Period was marked by significant changes in the Earth’s environment. This period saw the formation of the first shallow tropical seas, which were home to an incredible diversity of life. It was also during this time that the first continents began to form and the first land masses began to emerge from the oceans.

In conclusion, the Ordovician Period is a critical time interval in the history of the Earth, characterized by significant changes and diversification in the evolution of life on Earth, including the evolution of jawless and primitive jawed fish and the formation of the first shallow tropical seas. By studying the Ordovician Period, we can gain a deeper understanding of the history of the Earth and the evolution of life, and we can also learn about the interplay between environmental change and the evolution of species.

The Cambrian Period is a division of the Paleozoic Era and covers the time interval between 541 and 485 million years ago. It is the first period of the Paleozoic Era and precedes the Ordovician Period.

The Cambrian Period is particularly significant in the history of the Earth because it marks the beginning of the “Cambrian Explosion”, a time of rapid diversification in the evolution of life on Earth. During this time, the first complex life forms, such as trilobites, brachiopods, and mollusks, evolved. This was a major milestone in the evolution of life on Earth and represented a significant step forward in the development of complex organisms.

The Cambrian Period was also a time of significant environmental change on Earth. This period saw the formation of the first shallow seas, which were home to an incredible diversity of life. In addition, the first continents began to form and the first land masses began to emerge from the oceans.

In conclusion, the Cambrian Period is a critical time interval in the history of the Earth, characterized by the beginning of the “Cambrian Explosion” and the rapid diversification of life on Earth. By studying the Cambrian Period, we can gain a deeper understanding of the history of the Earth and the evolution of life, and we can also learn about the interplay between environmental change and the evolution of species.

The Proterozoic Eon is the second and the last of the three eons of the Precambrian era and covers the time interval between 2.5 billion and 541 million years ago. It follows the Archean Eon and precedes the Paleozoic Era.

The Proterozoic Eon was a time of significant change and evolution in the history of the Earth. During this time, the first multicellular life forms evolved, and the first primitive ecosystems were established. The Proterozoic Eon also saw the first signs of plate tectonics , the formation of the first supercontinents, and the development of the first oceanic crust.

One of the most significant events of the Proterozoic Eon was the evolution of oxygen-producing photosynthetic organisms, which eventually led to the buildup of free oxygen in the atmosphere. This had a profound effect on the evolution of life on Earth and set the stage for the evolution of complex life forms.

In conclusion, the Proterozoic Eon is a critical time interval in the history of the Earth, characterized by significant changes and evolution in the evolution of life on Earth, the first signs of plate tectonics, the formation of the first supercontinents, and the evolution of oxygen-producing photosynthetic organisms. By studying the Proterozoic Eon, we can gain a deeper understanding of the history of the Earth and the evolution of life, and we can also learn about the interplay between environmental change and the evolution of species.

The Archean Eon is the first of the three eons of the Precambrian era and covers the time interval between 4 billion and 2.5 billion years ago. It precedes the Proterozoic Eon and is the longest of the three eons in the Precambrian era.

The Archean Eon was a time of significant change and evolution in the history of the Earth. During this time, the first single-celled life forms evolved and the first primitive ecosystems were established. The Archean Eon also saw the formation of the first continents and the first stable environments suitable for life.

One of the most significant events of the Archean Eon was the emergence of the first living organisms. The exact origin of life on Earth is still uncertain, but the evidence suggests that life evolved sometime during the Archean Eon. This was a major milestone in the history of the Earth and represents a critical step forward in the evolution of life on our planet.

In conclusion, the Archean Eon is a critical time interval in the history of the Earth, characterized by significant changes and evolution in the evolution of life on Earth, the formation of the first continents and the first stable environments suitable for life, and the emergence of the first living organisms. By studying the Archean Eon, we can gain a deeper understanding of the history of the Earth and the evolution of life, and we can also learn about the interplay between environmental change and the evolution of species.

The Hadean Eon is the earliest and shortest of the three eons of the Precambrian era and covers the time interval between the formation of the Earth and the start of the Archean Eon, approximately 4 billion years ago.

During the Hadean Eon, the Earth was still in its early stages of formation, and the conditions were extremely harsh. The Earth’s surface was constantly bombarded by asteroids, comets, and other debris, resulting in frequent impacts and the formation of large craters. The early atmosphere was also composed of mostly hydrogen and helium, with little to no oxygen, making it hostile to life as we know it today.

Despite these harsh conditions, the Hadean Eon was a critical time in the history of the Earth, as it set the stage for the evolution of life. It was during this time that the first oceans formed, and the first minerals and rocks were created, providing the building blocks for life to eventually emerge.

In conclusion, the Hadean Eon is an important time interval in the history of the Earth, representing the earliest stage of the Earth’s formation and setting the stage for the evolution of life. Although the conditions during the Hadean Eon were harsh, it was a critical time in the history of the Earth, and by studying the Hadean Eon, we can gain a deeper understanding of the conditions that existed during the early formation of the Earth and the emergence of life on our planet.

Here is a list of references for further reading about the Geologic Time Scale:

“The Geologic Time Scale 2012.” Gradstein, F. M., Ogg, J. G., Schmitz, M. D., & Ogg, G. (2012). Elsevier.
“A revision of the geologic time scale.” Harper, D. A. T., & Owen, A. W. (2001). Geological Society, London, Special Publications, 190(1), 3-48.
“The geologic time scale.” Ogg, J. G., Ogg, G., & Gradstein, F. M. (2008). Episodes, 31(2), 120-124.
“The geologic time scale and the history of life on Earth.” Benton, M. J. (2013). Proceedings of the Royal Society B: Biological Sciences, 280(1755), 20131041.
“Geological time scales and biotic evolution.” Ernst, R. E., & Buchardt, B. (2008). Earth-Science Reviews, 89(1-2), 1-46.
“A new geological time scale with special reference to Precambrian and Neogene.” Harland, W. B. (1989). Journal of the Geological Society, 146(3), 489-495.
“Geologic Time Scales: A Survey of Methods and Developments.” Finney, S. C. (2005). In Geologic Time Scales (pp. 1-21). Springer Netherlands.

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Why would you want to name time?

When you refer to events in the history of your life you often link it to a time period. "When I was in kindergarten..." might be the start of your story. It helps scientists to have names to refer to events in Earth history. For this reason, they developed the geologic time scale.

The Geologic Time Scale

Earth formed 4.5 billion years ago. Geologists divide this time span into smaller periods. Many of the divisions mark major events in life history.

Dividing Geologic Time

Divisions in Earth history are recorded on the geologic time scale . For example, the Cretaceous ended when the dinosaurs went extinct. European geologists were the first to put together the geologic time scale. So, many of the names of the time periods are from places in Europe. The Jurassic Period is named for the Jura Mountains in France and Switzerland, for example.

Putting Events in Order

To create the geologic time scale, geologists correlated rock layers. Steno's laws were used to determine the relative ages of rocks. Older rocks are at the bottom, and younger rocks are at the top. The early geologic time scale could only show the order of events. The discovery of radioactivity in the late 1800s changed that. Scientists could determine the exact age of some rocks in years. They assigned dates to the time scale divisions. For example, the Jurassic began about 200 million years ago. It lasted for about 55 million years.

Divisions of the Geologic Time Scale

The largest blocks of time on the geologic time scale are called “eons.” Eons are split into “eras.” Each era is divided into “periods.” Periods may be further divided into “epochs.” Geologists may just use “early” or “late.” An example is “late Jurassic,” or “early Cretaceous.” Pictured below is the geologic time scale ( Figure below).

The Geologic Time Scale.

3 Geologic Time: From an Early Geologic Time Scale

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The time scale of geology—the first overarching precept in geology—and its development are the focus of this chapter. How did geologists determine the great age of the Earth through the spatial nature of geologic units and changes in fossils over time? There was no guidebook to the process of unraveling the Earth’s biography, and the discoveries proceeded step by step using observation and the development of hypotheses. Scientists such as Abraham Werner established principles to place rocks in order relative to one another, providing the beginning of understanding strata, their composition, sources, and life within them. Early estimates of the age of the Earth were on the order of thousands of years, carefully calculated based on the generations in the Bible. However, geologists such as James Hutton and Charles Lyell realized that the probable age of the Earth was much greater by examining the time it would take for processes, like sedimentation rates for a layer of sand or mud to be deposited to occur. From these observations, they deduced it would take orders of magnitude more time to build up great masses of rock layers, and the time scale of geology was extended millions of years.

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Geologic Time Scale

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Bibliography

Agterberg, F. P., Hammer, O., and Gradstein, F. M., 2012. Statistical procedures. In Gradstein, R., et al. (eds.), The Geologic Time Scale 2012 . Amsterdam: Elsevier, pp. 269–275.

Chapter Google Scholar

Cooper, R. A., and Sadler, P. M., 2012. The Ordovician period. In Gradstein, R. M., et al. (eds.), The Geologic Time Scale 2012 . Amsterdam: Elsevier, pp. 489–525.

Davydov, V. I., Korn, D., and Schmitz, M. D., 2012. The Carboniferous period. In Gradstein, R. M., et al. (eds.), The Geologic Time Scale 2012 . Amsterdam: Elsevier, pp. 603–653.

Gradstein, F. M., and Ogg, J. G., 1996. A Phanerozoic time scale. Episodes , 19 , 3–5. with insert.

Google Scholar

Gradstein, F. M., Ogg, J. G., Smith, A. G., Agterberg, F. P., Bleeker, W., Cooper, R. A., Davydov, V., Gibbard, P., Hinnov, L. A., House, M. R., Lourens, L., Luterbacher, H.-P., McArthur, J., Melchin, M. J., Robb, L. J., Shergold, J., Villeneuve, M., Wardlaw, B. R., Ali, J., Brinkhuis, H., Hilgen, F. J., Hooker, J., Howarth, R. J., Knoll, A. H., Laskar, J., Monechi, S., Powell, J., Plumb, K.A., Raffi, I., Röhl, U., Sanfilippo, A., Schmitz, B., Shackleton, N. J., Shields, G. A., Strauss, H., Van Dam, J., Veizer, J., van Kolfschoten, T. H., and Wilson, D., 2004. A Geologic Time Scale 2004 . Cambridge University Press, 589 pp.

Gradstein, F. M, Ogg, J. G., Schmitz, M. D., Ogg, G. M., Agterberg, F. P., Anthonissen, D. E., Becker, T. R., Catt, J. A., Cooper, R. A., Davydov, V. I., Gradstein, S. R., Henderson, C. M., Hilgen, F. J., Hinnov, L. A., McArthur, J. M., Melchin, M. J., Narbonne, G. M., Paytan, A., Peng, S., Peucker-Ehrenbrink, B., Pillans, B., Saltzman, M. R., Simmons, M. D., Shields, G. A., Tanaka, K. L.,Vandenberghe, N., Van Kranendonk, M. J., Zalasiewicz, J., Altermann, W., Babcock, L. E., Beard, B. L., Beu, A. G., Boyes, A. F., Cramer, B. D., Crutzen, P. J., van Dam, J. A., Gehling, J. G., Gibbard, P. L., Gray, E. T., Hammer, O., Hartmann, W. K., Hill, A. C., Paul F. Hoffman, P. F., Hollis, C. J., Hooker, J. J., Howarth, R. J., Huang, C., Johnson, C. M., Kasting, J. F., Kerp, H., Korn, D., Krijgsman, W., Lourens, L. J., MacGabhann, B. A., Maslin, M. A., Melezhik, V. A., Nutman, A. P., Papineau, D., Piller, W. E., Pirajno, F., Ravizza, G. E., Sadler, P. M., Speijer, R. P., Steffen, W., Thomas, E., Wardlaw, B. R., Wilson, D. S., and Xiao, S., 2012. The Geologic Time Scale 2012 . Boston: Elsevier, 1129 pp.

Harland, W. B., Cox, A. V., Llewellyn, P. G., Pickton, C. A. G., Smith, A. G., and Walters, R., 1982. A Geologic Time Scale . Cambridge: Cambridge University Press, 131 pp.

Harland, W. B., Armstrong, R. L., Cox, A. V., Craig, L. A., Smith, A. G., and Smith, D. G., 1990, A Geologic Time Scale 1989 . Cambridge: Cambridge University Press, 263 pp.

Hilgen, F. J., Lourens, L. J., and VanDam, J. A., 2012. The Neogene Period. In Gradstein, R. M., et al. (eds.), The Geologic Time Scale 2012 . Amsterdam: Elsevier, pp. 923–979.

Holmes, A., 1960. A revised geological time-scale. Transactions of the Edinburgh Geological Society , 17 , 183–216.

Article Google Scholar

Holmes, A., 1965. Principles of Physical Geology . London: Nelson Printers, 1288 p.

Kuiper, K. F., Deino, A., Hilgen, F. J., Krijgsman, W., Renne, P. R., and Wijbrans, J. R., 2008. Synchronizing rock clocks of Earth history. Science , 320 (5875), 500–504.

Narbonne, G., Xiao, S., and Shields, G. A., 2012. The Ediacaran period. In Gradstein, R. M. (ed.), The Geologic Time Scale 2012 . Amsterdam: Elsevier, pp. 413–437.

Ogg, J. G., Ogg, G., and Gradstein, F. M., 2008. The Concise Geologic Time Scale . Cambridge: Cambridge University Press, 177 pp.

Ogg, J. G., and Hinnov, L. A., 2012. The cretaceous period. In Gradstein, R. M., et al. (eds.), The Geologic Time Scale 2012 . Amsterdam: Elsevier, pp. 793–855.

Schmitz, M. D., 2012. Radiogenic isotopes geochronology. In Gradstein, R. M. (ed.), The Geologic Time Scale 2012 . Amsterdam: Elsevier, pp. 115–127.

Vanden Berghe, N., Hilgen, F. J., and Speijer, R. P., 2012. The Paleogene Period. In Gradstein, R. M., et al. (eds.), The Geologic Time Scale 2012 . Amsterdam: Elsevier, pp. 855–923.

Van Kranendonk, M., 2012. A chronostratigraphic division of the Precambrian. In Gradstein, R. M., et al. (eds.), The Geologic Time Scale 2012 . Amsterdam: Elsevier, pp. 299–393.

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Gradstein, F.M. (2016). Geologic Time Scale. In: Harff, J., Meschede, M., Petersen, S., Thiede, J. (eds) Encyclopedia of Marine Geosciences. Encyclopedia of Earth Sciences Series. Springer, Dordrecht. https://doi.org/10.1007/978-94-007-6238-1_199

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The Four Eras of the Geologic Time Scale

The Precambrian, Paleozoic, Mesozoic, and Cenozoic Eras

United States Geological Survey/Wikimedia Commons/Public Domain

History Of Life On Earth
Human Evolution
Natural Selection
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The Geologic Time Scale is the history of the Earth broken down into four spans of time marked by various events, such as the emergence of certain species, their evolution, and their extinction, that help distinguish one era from another. Strictly speaking, Precambrian Time is not an actual era due to the lack of diversity of life, however, it's still considered significant because it predates the other three eras and may hold clues as to how all life on Earth eventually came to be.

Precambrian Time: 4.6 billion to 542 Million Years Ago

Precambrian Time started at the beginning of the Earth 4.6 billion years ago. For billions of years, there was no life on the planet. It wasn't until the end of Precambrian Time that single-celled organisms came into existence. No one is certain how life on Earth began, but theories include the Primordial Soup Theory , Hydrothermal Vent Theory , and Panspermia Theory .

The end of this time span saw the rise of a few more complex animals in the oceans, such as jellyfish. There was still no life on land, and the atmosphere was just beginning to accumulate the oxygen required for higher-order animals to survive. Living organisms wouldn't proliferate and diversify until the next era.

Paleozoic Era: 542 Million to 250 Million Years Ago

Jose A. Bernat Bacete/Getty Images

The Paleozoic Era began with the Cambrian Explosion, a relatively rapid period of speciation that kicked off a long period of life flourishing on Earth. Vast amounts of life forms from the oceans moved onto the land. Plants were the first to make the move, followed by invertebrates. Not long afterward, vertebrates took to the land. Many new species appeared and thrived.

The end of the Paleozoic Era came with the largest mass extinction in the history of life on Earth, wiping out 95% of marine life and nearly 70% of life on land. Climate changes were most likely the cause of this phenomenon as the continents all drifted together to form Pangaea. As devastating this mass extinction was, it paved the way for new species to arise and a new era to begin.

Mesozoic Era: 250 Million to 65 Million Years Ago

After the Permian Extinction caused so many species to go extinct, a wide variety of new species evolved and thrived during the Mesozoic Era, which is also known as the "age of the dinosaurs" since dinosaurs were the dominant species of the age.

The climate during the Mesozoic Era was very humid and tropical, and many lush, green plants sprouted all over the Earth. Dinosaurs started off small and grew larger as the Mesozoic Era went on. Herbivores thrived. Small mammals came into existence, and birds evolved from the dinosaurs.

Another mass extinction marked the end of the Mesozoic Era, whether triggered by a giant meteor or comet impact, volcanic activity, more gradual climate change, or various combinations of these factors. All the dinosaurs and many other animals, especially herbivores, died off, leaving niches to be filled by new species in the coming era.

Cenozoic Era: 65 Million Years Ago to the Present

Dorling Kindersley/Getty Images

The final time period on the Geologic Time Scale is the Cenozoic Period. With large dinosaurs now extinct, smaller mammals that had survived were able to grow and become dominant.

The climate changed drastically over a relatively short period of time, becoming much cooler and drier than during the Mesozoic Era. An ice age covered most temperate parts of the Earth with glaciers, causing life to adapt relatively rapidly and the rate of evolution to increase.

All species of life—including humans—evolved into their present-day forms over the course of this era, which hasn't ended and most likely won't until another mass extinction occurs.

Mesozoic Era
The 5 Major Mass Extinctions
The Cenozoic Era Continues Today
Geologic Time Scale: Eons, Eras, and Periods
Periods of the Paleozoic Era
Life on Earth During the Precambrian Time Span
Periods of the Cenozoic Era
Geologic Time Scale: Eons and Eras
What Is Mass Extinction?
Cretaceous-Tertiary Mass Extinction
The Cenozoic Era (65 Million Years Ago to the Present)
Learn About the Different Dinosaur Periods
Tectonic Plates' Effect on Evolution
The Earth's 10 Biggest Mass Extinctions
Prehistoric Life During the Permian Period
The Triassic-Jurassic Mass Extinction

The Importance of the Geologic Time Scale: A Guide for Geoscientists

Summary: the geological time scale is a way to organize and divide Earth’s history based on significant geological events such as mass extinctions, climate changes, and the appearance of new species. Geologists use this scale to understand and predict the behavior of the planet, as well as to identify natural resources such as oil, gas, and minerals. The scale is divided into eons, eras, periods, and epochs, with each division based on important geological events that occurred during Earth’s history. While the scale is not based on equal time intervals, it provides a framework for understanding the history of our planet.

What is the geologic time scale?

The geological time scale is the way geologists and geoscientists divide time since planet Earth was formed. This scale arose from the need to organize all the geological events that have occurred during the life of planet earth.

Thus, the geological time scale is subdivided taking into account various events such as mass extinctions, climate changes, appearance of new species, formation of continents, mountains, and various other events.

What is the significance of the geologic time scale?

Its importance lies in the fact that it helps geologists and scientists to correlate various past events to try to predict the behavior of the planet now and in the future.

Furthermore, all these past geological events are directly related to natural resources such as the formation of oil, gas and mineral deposits that are currently used for economic development. Thus, this scale is also used by mining engineers.

Therefore the geological time scale is the division of the earth’s history taking into account several important geological events.

Division of the geologic time scale

Those in charge of dividing this scale are geologists, who have not done so taking into account only days and hours. This scale is divided even with time intervals greater than millions of years and its subdivisions are varied, that is, they do not have an equal time limit in all divisions.

This is because geologic time is divided using important events in Earth’s history.

Example of division of the geologic time scale

For example, to set the limit between the Permian and Triassic, it is done taking into account a global extinction that occurred that ended a large percentage of the life of animals and plant species on earth.

Another interesting example is the limit between the Precambrian and the Paleozoic, which is delimited by the appearance of the first animals with hard parts in their body structure.

General structure of the geologic time scale

The eons are those intervals in the larger scale or with more geological time duration, generally representing a separation of hundreds of millions of years. If you look at the geological time scale in pdf, you will be able to notice that the Phanerozoic eon is the most recent and its beginning was delimited 500 million years ago.

The eras are the subdivisions that are made to the eons. Likewise, in the geological time scale in pdf, it is observed, for example, that the Phanerozoic is divided into eras: the Cenozoic, the Mesozoic and the Paleozoic eras. These eras are divided equally by major and rare events that occurred on the planet.

The eras are the small divisions that are made to the periods. The periods are delimited with geological events that are not as important or relevant as those of the eras and eons. The geologic time scale pdf shows that the Paleozoic is subdivided into the Permian, Pennsylvanian, Mississippian, Devonian, Silurian, Ordovician, and Cambrian periods.

Epochs are much finer subdivisions of time, however keep in mind that the Cenozoic periods are often subdivided into times . This type of subdivision is done only for those most recent slices on the time scale.

This occurs because the oldest rocks have undergone various geological processes such as deformation, burial, metamorphism, alteration and for this reason they cannot be clearly interpreted.

What is petrography importance and applications.

Petrography is a branch that belongs to petrology and general geology, and that basically deals with the description of rocks. The description consists of analyzing…

A Detailed Exploration of Geological Faults and Their Characteristics

Basically, geological faults are fractures that occur in the earth’s crust along which there has been an appreciable displacement of rocks or soils. These geological…

Environmental Geology: Definition and Importance

Geology is the science of processes related to the composition, structure, and history of the Earth and its life. Geology is an interdisciplinary science that…

Geomorphology: The Study of Earth’s Relief and Its Implications

Despite the fact that geomorphology is confused with geology and sometimes with geography, it should be clarified that it is a very extensive science or…

Geological Time Scale of Earth – Geography Notes

The geological time scale is a vital tool for scientists studying the history of the Earth, including the evolution of life and the changes in Earth’s climate and geology over time. By dividing time into eons, eras, periods, and epochs, scientists can organize and study the events that have occurred throughout Earth’s history.
Fossils provide a record of past life on Earth, and the distribution of fossils through time can help scientists identify when certain organisms evolved or went extinct.
The subdivisions of the geological time scale are arranged in a hierarchical manner with eons being the largest units of time and epochs being the smallest.
The geological time scale provides a framework for the study of Earth’s history and the evolution of life on the planet.
By dividing geological time into smaller, more manageable units, scientists can better understand the sequence of events and the relationships between them.

Table of Contents

Division of Geological Time Scale

It’s important to note that the Geological Time Scale (GTS) is a way to divide Earth’s history into different time intervals based on significant geological events and changes. This allows scientists to study and understand the Earth’s history and how it has evolved over time.

Here’s a summary of the different subunits of the GTS:

The largest time period of the GTS, represents billions of years. There are only four eons in Earth’s history: the Hadean, Archean, Proterozoic, and Phanerozoic.

A division of an eon, representing tens to hundreds of millions of years. The Phanerozoic eon, which began about 541 million years ago, is divided into three eras: the Paleozoic, Mesozoic, and Cenozoic.

A division of an era, representing millions of years to tens of millions of years. For example, the Mesozoic era is divided into three periods: the Triassic, Jurassic, and Cretaceous.

A division of a period, representing hundreds of thousands of years to tens of millions of years. The Cenozoic era is divided into three epochs : the Paleogene, Neogene, and Quaternary.

It’s worth noting that the boundaries between these subunits of the GTS are not always well-defined, and may vary depending on the region being studied. The GTS is constantly being updated and revised as new data and discoveries are made.

The Hadean eon (4,540 – 4,000 mya) represents the time before a reliable (fossil) record of life.
Temperatures are extremely hot, and much of the Earth was molten because of frequent collisions with other bodies, extreme volcanism, and the abundance of short-lived radioactive elements.
A giant impact collision with a planet-sized body named Theia (approximately 4.5 billion years ago) is thought to have formed the Moon.
The moon was subjected to Late Heavy Bombardment (LHB – lunar cataclysm – 4 billion years ago).
During the LHB phase, a disproportionately large number of asteroids are theorized to have collided with the early terrestrial planets in the inner Solar System, including Mercury, Venus, Earth, and Mars.
Volcanic outgassing probably created the primordial atmosphere and then the ocean.
The early atmosphere contained almost no oxygen.
Over time, the Earth cooled, causing the formation of a solid crust, leaving behind hot volatiles which probably resulted in a heavy CO2 atmosphere with hydrogen and water vapor.
Liquid water oceans exist despite the surface temperature of 230° C because, at an atmospheric pressure of above 27 atmospheres, caused by the heavy CO2 atmosphere, water is still liquid.
As the cooling continued, dissolving in ocean water removed most CO2 from the atmosphere.
Hydrogen and helium are expected to continually escape (even to the present day) due to atmospheric escape.

Archean Eon

The beginning of life on Earth and evidence of cyanobacteria date to 3500 mya.
Life was limited to simple single-celled organisms lacking nuclei, called Prokaryota.
The atmosphere was without oxygen, and the atmospheric pressure was around 10 to 100 atmospheres.
The Earth’s crust had cooled enough to allow the formation of continents.
The oldest rock formations exposed on the surface of the Earth are Archean .

Volcanic activity was considerably higher than today, with numerous lava eruptions.
The oceans were more acidic due to dissolved carbon dioxide than during the Proterozoic.
By the end of the Archaean , plate tectonics may have been similar to that of the modern Earth.
Liquid water was prevalent, and deep oceanic basins are known to have existed
The earliest stromatolites are found in 3.48 billion -year-old sandstone discovered in Western Australia.
The earliest identifiable fossils consist of stromatolites, which are microbial mats formed in shallow water by cyanobacteria.

Proterozoic Eon

It is the last eon of the Precambrian “supereon” .
It spans from the time of the appearance of oxygen in Earth’s atmosphere to just before the proliferation of complex life (such as corals) on Earth.
Bacteria begin producing oxygen, leading to the sudden rise of life forms.
Eukaryotes (have a nucleus), emerge, including some forms of soft-bodied multicellular organisms.
Earlier forms of fungi formed around this time.
The early and late phases of this eon may have undergone Snowball Earth periods (the planet suffered below-zero temperatures, extensive glaciation, and as a result drop in sea levels).
Snowball Earth: The Snowball Earth hypothesis proposes that Earth’s surface became entirely or nearly entirely frozen at least once, sometime earlier than 650 Mya (million years ago).

It was a very tectonically active period in the Earth’s history.
It featured the first definitive supercontinent cycles and modern orogeny (mountain building).
It is believed that 43% of modern continental crust was formed in the Proterozoic, 39% formed in the Archean, and only 18% in the Phanerozoic.
In the late Proterozoic (most recent), the dominant supercontinent was Rodinia (~1000–750 Ma).

Phanerozoic Eon

The boundary between the Proterozoic and the Phanerozoic eons was set when the first fossils of animals such as trilobites appeared.
Life remained mostly small and microscopic until about 580 million years ago, when complex multicellular life arose, developed over time, and culminated in the Cambrian Explosion about 541 million years ago.
Plant life on land appeared in the early Phanerozoic eon .
Complex life, including vertebrates, begin to dominate the Earth’s ocean.
Pangaea forms and later dissolves into Laurasia and Gondwana.
Gradually, life expands to land and all familiar forms of plants, insects, animals and fungi begin appearing.
Birds, the descendants of dinosaurs, and more recently mammals emerge.
Modern animals—including humans—evolve at the most recent phases of this eon (2 million years ago).

The Phanerozoic eon is divided into three eras:

The Palaeozoic , an era of arthropods, amphibians, fishes, and the first life on land;
The Mesozoic , which spanned the rise, reign of reptiles, the climactic extinction of the non-avian dinosaurs, the evolution of mammals and birds; and
The Cenozoic, which saw the rise of mammals.
The Phanerozoic is divided into three eras: the Paleozoic, Mesozoic, and Cenozoic, which are further subdivided into 12 periods.

Frequently Asked Questions (FAQs)

1. what is the geological time scale, and why is it important.

Answer: The Geological Time Scale is a framework that divides Earth’s history into distinct intervals based on significant geological and biological events. It helps scientists organize and understand the vast expanse of Earth’s history, providing a chronological sequence of major events such as mass extinctions, evolutionary developments, and geological processes. This scale is crucial for studying the history of life on Earth and for interpreting geological processes that have shaped the planet over billions of years.

2. How is the Geological Time Scale divided, and what are the major units?

Answer: The Geological Time Scale is divided into hierarchical units, with the largest units being eons, followed by eras, periods, epochs, and ages. The current division of time includes the Phanerozoic Eon (the most recent eon), which is further divided into the Cenozoic, Mesozoic, and Paleozoic eras. Each era is then subdivided into periods, and periods into epochs. For example, the Cenozoic Era includes the Paleogene and Neogene periods, and the Quaternary epoch, where we find the present Holocene epoch. This hierarchical structure allows scientists to categorize and discuss specific intervals in Earth’s history.

3. How do scientists determine the ages of rocks and events in the Geological Time Scale?

Answer: Scientists use various methods to determine the ages of rocks and events in the Geological Time Scale. One common method is radiometric dating, which involves measuring the decay of radioactive isotopes in rocks. For example, the decay of uranium to lead is often used for dating rocks. Fossils are another crucial tool for dating, as certain organisms existed only during specific time periods. Additionally, stratigraphy, the study of rock layers and their sequence, helps establish the relative ages of rocks and events. By combining these methods, scientists create a comprehensive timeline of Earth’s history in the Geological Time Scale.

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8.1: The Geological Time Scale

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Steven Earle
Vancover Island University via BCCampus

William Smith worked as a surveyor in the coal-mining and canal-building industries in southwestern England in the late 1700s and early 1800s. While doing his work, he had many opportunities to look at the Paleozoic and Mesozoic sedimentary rocks of the region, and he did so in a way that few had done before. Smith noticed the textural similarities and differences between rocks in different locations, and more importantly, he discovered that fossils could be used to correlate rocks of the same age. Smith is credited with formulating the principle of faunal succession (the concept that specific types of organisms lived during different time intervals), and he used it to great effect in his monumental project to create a geological map of England and Wales, published in 1815. For more on William Smith, including a large-scale digital copy of the famous map, see the William Smith Wikipedia page.

Inset into Smith’s great geological map is a small diagram showing a schematic geological cross-section extending from the Thames estuary of eastern England all the way to the west coast of Wales. Smith shows the sequence of rocks, from the Paleozoic rocks of Wales and western England, through the Mesozoic rocks of central England, to the Cenozoic rocks of the area around London (Figure \(\PageIndex{1}\)). Although Smith did not put any dates on these—because he didn’t know them—he was aware of the principle of superposition (the idea, developed much earlier by the Danish theologian and scientist Nicholas Steno, that young sedimentary rocks form on top of older ones), and so he knew that this diagram represented a stratigraphic column. And because almost every period of the Phanerozoic is represented along that section through Wales and England, it is a primitive geological time scale.

Smith’s work set the stage for the naming and ordering of the geological periods, which was initiated around 1820, first by British geologists, and later by other European geologists. Many of the periods are named for places where rocks of that age are found in Europe, such as Cambrian for Cambria (Wales), Devonian for Devon in England, Jurassic for the Jura Mountains in France and Switzerland, and Permian for the Perm region of Russia. Some are named for the type of rock that is common during that age, such as Carboniferous for the coal- and carbonate-bearing rocks of England, and Cretaceous for the chalks of England and France.

The early time scales were only relative because 19th century geologists did not know the ages of the rocks. That information was not available until the development of isotopic dating techniques early in the 20th century.

The geological time scale is currently maintained by the International Commission on Stratigraphy (ICS), which is part of the International Union of Geological Sciences. The time scale is continuously being updated as we learn more about the timing and nature of past geological events. You can view the ICS time scale online. It would be a good idea to print a copy (in color) to put on your wall while you are studying geology.

Geological time has been divided into four eons: Hadean (4570 to 4850 Ma), Archean (3850 to 2500 Ma), Proterozoic (2500 to 540 Ma), and Phanerozoic (540 Ma to present). As shown in Figure \(\PageIndex{2}\), the first three of these represent almost 90% of Earth’s history. The last one, the Phanerozoic (meaning “visible life”), is the time that we are most familiar with because Phanerozoic rocks are the most common on Earth, and they contain evidence of the life forms that we are familiar with to varying degrees.

The Phanerozoic eon—the past 540 Ma of Earth’s history—is divided into three eras: the Paleozoic (“early life”), the Mesozoic (“middle life”), and the Cenozoic (“new life”), and each of these is divided into a number of periods (Figure \(\PageIndex{3}\)). Most of the organisms that we share Earth with evolved at various times during the Phanerozoic.

The Cenozoic era, which represents the past 65.5 Ma, is divided into three periods: Paleogene, Neogene, and Quaternary, and seven epochs (Figure \(\PageIndex{4}\)). Dinosaurs became extinct at the start of the Cenozoic, after which birds and mammals radiated to fill the available habitats. Earth was very warm during the early Eocene and has steadily cooled ever since. Glaciers first appeared on Antarctica in the Oligocene and then on Greenland in the Miocene, and covered much of North America and Europe by the Pleistocene. The most recent of the Pleistocene glaciations ended around 11,700 years ago. The current epoch is known as the Holocene. Epochs are further divided into ages (a.k.a. stages), but we won’t be going into that level of detail here.

Most of the boundaries between the periods and epochs of the geological time scale have been fixed on the basis of significant changes in the fossil record. For example, as already noted, the boundary between the Cretaceous and the Paleogene coincides exactly with a devastating mass extinction. That’s not a coincidence. The dinosaurs and many other types of organisms went extinct at this time, and the boundary between the two periods marks the division between sedimentary rocks with Cretaceous organisms (including dinosaurs) below, and Paleogene organisms above.

Image Descriptions

[Return to Figure \(\PageIndex{3}\)]

[Return to Figure \(\PageIndex{4}\)]

Media Attributions

Figure \(\PageIndex{1}\): “Sketch of the succession of strata and their relative altitudes” by William Smith. Adapted by Steven Earle. Public domain.
Figures 8.1.2, 8.1.3, 8.1.4: © Steven Earle. CC BY.

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24 Geological Time Scale

M. Manibabu Singh

Table of contents:

1. Introduction

2. Early Principles Behind Geologic Time

3. Construction Of Geologic Time Scale (GTS)

4. The Time Scale Creator

5. Recognizing Geologic Stages

6. Divisions Of Geologic Time

6.1 Proterozoic Or Precambrian Eon

6.2 The Palaozoic Era

6.3 The Mesozoic Era

6.4 The Cenozoic Era

Learning outcomes

To know about the geological time scale
To understand the early Principles Behind Geologic Time
To know about the construction Of Geologic Time Scale (GTS)
To know and understand its divisions

1. Introduction

The geography and landscape of a region are always changing. Geological research works reveal that the mountains and valleys that surround us or the position of the coastline today have not always been as we know them now. The land that we walk on, in the majority of cases, has risen up from the depths of an ancient sea, and the distribution of land and sea will change through time. These changes result from complex geological processes: sediments that are transformed into new rocks and erosion of rocks that already exist into sediments; uplift or emergence of land areas, with the consequent retreat of the sea, and flooding of other areas, that are invaded by seas and oceans, where accumulation of sediment starts again that will later be transformed into other rocks, followed by renewed emergence and further destruction, etc. By studying the internal structure and composition of rocks, their age (that measured in millions of years) and the way that they are distributed in a region, geologists can reconstruct the way in which the landscape and geography of the region has changed, when the mountains were uplifted that are emerged now, and so on. All of these geological processes are extraordinarily slow from a human perspective, the duration of which is counted in terms of millions of years.

Geologists now able to reconstruct the sequence of events that has shaped the Earth‘s surface from the study of petrology, stratigraphy and palaeontology. Many events have occurred since the formation of the Earth about 4.5 billion years ago (or 4500 million years ago). Some of these events have been recorded in the rocks that make up the crust. A chronological organization of these events is recorded on a geologic time scale as a framework for deciphering the history of our planet, Earth. This system of chronological measurement that relates stratigraphy to time, to describe the timing and relationships between events that have occurred throughout Earth’s history is termed as the Geologic Time Scale (GTS) . The geological time has started with the deposition of sedimentary rocks; the oldest stratum was created about some four and half billion years ago.

2. Early Principles behind Geologic Time

The history of systematic principle of Geologic time begins with a number of works by Geologists and the like since early centuries. Mention may be made of the work of one Danish physician Nicholas Steno (1638-1687) in 1669 who described how the position of a rock layer could be used to show the relative age of the layer. He devised three main principles that underlie the interpretation of geologic time and these principles have formed the framework for the geologic area of stratigraphy, which is the study of layered rock. The first is the principle of superposition which points out that in an undisturbed pile sediments, layer on the bottom was deposited first and so is the oldest, followed in succession by the layers above them, and the topmost one being the youngest in formation. The second one is the principle of horizontality, which states that all rock layers were originally deposited horizontally. The third, that is, the principle of original lateral continuity refers that originally deposited layers of rock extend laterally in all directions until either thinning out or being cut off by a different rock layer.

Contribution of a Scottish physician and geologist James Hutton (1726-1797) was the theory of ‗uniformitarianism‘ – which states that the surface of the earth was an ever-changing environment and ―the past history of our globe must be explained by what can be seen to be happening now‖. The theory of uniformitarianism states that the continuing uniformity of existing processes/physical laws is responsible for present and past conditions on earth. This theory was later well-known with a catch-phrased ―the present is the key to the past‖.

Another significant work was by William Smith, a surveyor by profession who was in charge of mapping a large part of England. He was the first to understand that certain rock units could be identified by the particular assemblages of fossils they contained. Using this information, he was able to correlate strata with the same fossils for many miles, giving rise to the principle of biologic succession. This principle states that: each age in the earth‘s history is unique such that fossil remains will be unique. This permits vertical and horizontal correlation of the rock layers based on fossil species.

The English Geologist, Charles Lyell‘s work (―Principles of Geology‖) during the early 1800s had significant contributions in framing the foundation of Geologic time scale – where he proposed two important principles – i ) the principle of cross-cutting relationships and ii) Inclusion principle. His first principle states that a rock feature that cuts across another feature must be younger than the rock that it cuts. The second principle, the Inclusion principle, proposes that small fragments of one type of rock but embedded in a second type of rock must have formed first, and were included when the second rock was forming.

3. Construction of Geologic Time Scale (GTS)

In fact the geologic time scale is the framework for deciphering the history of the Earth and has three important components (Gradstein, et. al. 2004) –

(1) The international chronostratigraphic divisions and their correlation in the global rock record,

(2) The means of measuring absolute (linear) time or elapsed durations from the rock record, and

(3) The methods of effectively joining the two scales.

In general the rock record of Earth‘s history is subdivided in a ―chronostratigraphic‖ scale of standardized global stratigraphic units, and is based on relative time units, in which global reference points at boundary stratotypes define the limits of the main formalized units, such as ―Devonian‖. The chronostratigraphic scale is an agreed convention, whereas its calibration to absolute (linear) time is a matter for discovery or estimation. No geologic time scale can be final on the fact that there occur continual improvements in data coverage, methodology, and standardization of chronostratigraphic units (Gradstein, et. al. 2004). There have been major developments in Geological Time Scale research has since 1989 by various international forums. Mention may be made of the works of the International Commission on Stratigraphy (ICS) mainly on refining the international chronostratigraphic scale, such as in the Ordovician or Permian periods, traditional European- or Asian-based geological stages have been replaced with new subdivisions that allow global correlation. Moreover, numerous high-resolution radiometric dates have been generated that has led to improved age assignments of key geologic stage boundaries. The use of global geochemical variations, Milankovitch climate cycles, and magnetic reversals has become important calibration tools (Gradstein, et. al. 2004).

4. The Time Scale Creator

One goal of ICS is to provide detailed global and regional ―reference‖ scales of Earth history. Such scales summarize our current consensus on the inter-calibration of events, their relationships to international divisions of geologic time and their estimated numerical ages. On-screen display and production of user-tailored time-scale charts is provided by the Time-Scale Creator , a public JAVA package available from the ICS website ( www.stratigraphy.org ) and www.tscreator.com , (Gradstein and Ogg, 2006).

5. Recognizing Geologic Stages

Geologic stages are recognized through their fossil content and not by their boundaries. Since the morphology of fossil taxa and their unique range in the rock record form the most unambiguous way to assign a relative age, these are used as the main method to distinguish and correlate strata among different regions. Obviously the evolutionary successions and assemblages of each fossil group are generally grouped into zones. And, the T S Creator program ( www.tscreator.com ) includes a majority of zonations and/or event datums (first or last appearances) for widely used groups of fossils through time. Trends and excursions in stable-isotope ratios, especially of carbon 12/13 and strontium 86/87, have become an increasingly reliable method to correlate among regions.

Geologists recognize two major segments in the geologic time scale called ‗ eons ‘. Eons is divided into three smaller time units called ‗ eras ‘. Eons refer to the longest subdivision based on the abundance of certain fossils recorded. Eras are the next subdivision to eons , marked by major changes in the fossil record. Eras are again divided into ‗ periods ‘ based on types of life existing at the time. Periods, in turn, have ‗ epochs ‘, the shortest subdivision marked by differences in life forms and can vary from continent to continent. Constant efforts by Geologists could make improvement of our knowledge of Earth history, and simultaneously attaining an advanced state of standardization in naming the units that elucidate this history. The time scale is expressed both in physical rock units and in abstract time units, the latter often with a numerical uncertainty. The two come together in time/rock units, or chronostratigraphic units in the geological vernacular.

Thus, eras, periods and epochs are by themselves the subdivisions of Earth‘s geologic timescale; these refer what happens during these intervals that gives each their unique characteristics. The progression from one stage to another is marked by some easily distinguishable, global stratigraphic ‗event‘, such as a mass extinction, bulk change in the composition of sedimentary rocks or shift from one climate regime to another, change in the composition of organism.

‗Ages‘ are expressed in units of million years measured back in time. Geologists use the designation ‗ Ma ’ to mean ‗millions of years ago‘ and ‗ My ’ to indicate a ‗million years of time‘. It is sometimes hard to imagine how long the geologic ages were and how far away from us in time they are. We can get a better idea if we scale the time. We can compress millions of years in a meter of space. To get the best idea of the different lengths of the ages we need to make two different scales, one for all of geologic time (all 4500 my) and the other for the fossil record.

6. Divisions of Geologic Time

The developing framework for discussing the Earth‘s history is known as the geologic time scale (GTS) and has been based largely on the fossil record. The subdivisions based on the hierarchical system of time intervals are identified by a characteristic assemblage of fossil forms and plate tectonics. The modern geologic time scale, in which the interval boundaries are also identified by their age as resolved through radiometric dating, was pioneered by Arthur Holmes.

In the GTS, Earth‘s history is divided broadly into two Eons, – Proterozoic or Precambrian Eon (4500-635 Ma), the earlier and Phanerozoic (635 Ma till present), the later. Within the first, Proterozoic or Precambrian Eon, there has three components, that is, Hadean, Archean and Proterozoic. The Hadean refers to a period of time which has no rock record. The Archean that followed corresponds to the ages of the oldest known rocks on earth. The Phanerozoic Eon has three eras – Palaeozoic, Mesozoic and Cenozoic , which in turn are divided into ‗Periods‘ and ‗Epochs‘.

6.1 PROTEROZOIC or PRECAMBRIAN EON

Precambrian that spans 88 percent of Earth history is taken to be started its time period from the time of initial accretion and differentiation (ca. 4560 Ma) to the first appearance of abundant hard-bodied fossils (the onset of the Cambrian Period at 541 Ma) (Gradstein, et.al. 2005). And, there is no coherent view of a geological time scale to help describe, analyze, calibrate, and communicate the evolution of planet Earth ( ibid ).

The Precambrian time scale, being incomplete and flawed (e.g., Cloud, 1987; Crook, 1989; Nisbet, 1991; Bleeker, 2003), is generally defined in terms of arbitrary, strictly chronometric, absolute age boundaries that are divorced from the only primary, objective, record of planetary evolution: the extant rock record (Gradstein, et.al. 2005). NUNA Conference (Geological Association of Canada), 2003 under the co-sponsorship of the International Committee on Stratigraphy (ICS), had a broad consensus that this arbitrarily defined Precambrian time scale fails to convey the richness of the Precambrian rock record. It has been suggested that ‗the Precambrian time scale should be (re)defined in terms of the only objective physical standard we have, the extant rock record. Boundaries should be placed at key events or transitions in the stratigraphic record, to highlight important milestones in the evolution of our planet. This would be analogous to the ―golden spike‖ GSSP approach employed in the Phanerozoic‘ (Gradstein, et.al. 2005). ‗Golden spike‘ is an informal term for a physical point in a stratigraphic section that defines a chronostratigraphic boundary. Pioneered by the Stratigraphic Committee of the London Geological Society , the ―golden spike‖ has been useful in resolving intractable and unending problems arising from conceptual definitions. (Delson, et.al. 2000: 607)

Hadean: Hadean (4.5 to 4 billion years ago, – GTS 2012 ) is not a geological period as such, and is characterized by the intense bombardment and its consequences, but no preserved supracrustals (Cloud, 1972). There is no evidence of rock formation during the time, except the meteorites. During Hadean time, the Solar System was forming, probably within a large cloud of gas and dust around the sun, called an accretion disc. The relative abundance of heavier elements in the Solar System suggests that this gas and dust was derived from a supernova, or supernovas – explosion of an old, massive star. It is a general observation that the sun formed within such a cloud of gas and dust, shrinking in on itself by gravitational compaction until it began to undergo nuclear fusion and give off light and heat. Surrounding particles began to coalesce by gravity into larger lumps, or planetesimals, which continued to aggregate into planets and the “left-over” materials formed asteroids and comets. The Earth and other planets would have been molten at the beginning because of collisions between large planetesimals release a lot of heat. Solidification of the molten material into rock happened as the Earth cooled. The oldest meteorites and lunar rocks are about 4.5 billion years old, but the oldest Earth rocks currently known are 3.8 billion years. It is also suggested that the surface of the Earth changed from liquid to solid sometime during the first 800 million or so years of its history. Once solid rock formed on the Earth, its geological history began. This most likely happened prior to 3.8 billion years, but hard evidence for this is lacking. The advent of a rock record roughly marks the beginning of the Archean eon.

Archean: The Archean eon (spanned about 1.5 billion years) has four eras: the Neoarchean (2.8 to 2.5 billion years ago), Mesoarchean (3.2 to 2.8 billion years ago), Paleoarchean (3.6 to 3.2 billion years ago), and Eoarchean (4 to 3.6 billion years ago). The GTS 2012 gave the time span of this eon within 4000-2500 Ma. During Archean there increased crustal record from the oldest supracrustals of Isua greenstone belt to the onset of giant iron formation deposition in the Hamersley basin, likely related to increasing oxygenation of the atmosphere. Earth’s crust cooled enough that rocks and continental plates began to form. During its early period life first appeared on Earth and the oldest fossils comprise that of bacteria microfossils, date to roughly 3.5 billion years ago. Stromatolites, the photosynthetic bacteria, as fossils are found abundantly at the Archean coast, in the early Archean rocks of South Africa and Western Australia. These fossils increased in abundance throughout the Archean, began to decline during the Proterozoic.

Fig:2- Stromatolite fossil (Archean)

Proterozoic: Proterozoic Eon experienced first stable continents, nearly modern plate-tectonic Earth but without metazoan life, except at its very top. Land masses gather to make up a continent called ―Rodinia‖ First abundant fossils of living organisms (bacteria, archaeans, eukaryotic cells) are evident with first evidence of oxygen build-up in the atmosphere. Cyanobacteria begins producing free oxygen (photosynthesis) GTS 2012 gave its time span between 2500-635 Ma.

6.2 THE PALAOZOIC ERA (― Age of Invertebrates ‖)

Next to Proterozoic is the Palaeozoic Era which is divided into seven different periods, such as – Vendian, Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian.

1. Vendian or Ediacaran: Vendian or Ediacaran refers to the first period of the Palaeozoic era lasting from about 635 to 541 million years ago ( Ma ), and is characterized by macroscopic fossils of soft-bodied organisms. Kimberella, Dickinsonia and Pteridinium are some of the Vendian fossils of great attention to the palaeontologists which occur in the Vendian rocks. Kimberella , a bilaterally symmetric animal that had rigid parts appears to be somewhat like a mollusc, and these are known from Vendian rocks of South Australia, and also Pteridinium having an elongated, ribbed body from Namibia and North Carolina.

A period first proposed by one Boris Sokolov, a Russian geologist and palaeontologist in 1952, the Vendian concept was developed stratigraphically top-to-down, that is, the lower boundary of the Cambrian became the upper boundary of the Vendian (Sokolov 1952, 1997). Vendian Period overlaps the Ediacaran period which is also taken to be synonymous to the former. Unlike later portions of the geologic time scale, the Vendian has neither formal subdivisions nor distinct early boundary. This is in large part due to the fact that it has only recently become a subject of interest to paleontologists. The genesis of the term Ediacaran period traced back with an exploratory work in 1946 by an Australian mining geologist named Reginald C. Sprigg in the Ediacara Hills on the western edge of the Flinders Ranges to north of Adelaide city, South Australia – where he found well-preserved fossilized imprints of eponymous biota of what were apparently soft-bodied organisms (which Sprigg referred to as ‗medusoids‘) mostly on the undersides of slabs of quartzite and sandstone. He could also establish their chronology to the late Precambrian period. In fact, the Ediacara Hills gave a name to the entire “Ediacara biota” of the late Precambrian. The Ediacaran Period as a geological period was officially ratified in 2004 by the International Union of Geological Sciences (IUGS) (Knoll, et.al 2004a, b; 2006).

3. Ordovician: The third period under the Paleozoic eon bears the first traces of vertebrates. The first animals with bones appear, though dominant animals are still trilobites, brachiopods and corals. Primitive fish, seaweeds and mollusks appear at this time. The beginning of this period has been dated between 485.4 to 443.8 Ma (GTS 2012). This epoch experienced very cold climatic condition. Important developments include the beginning of the construction of South Carolina and formations of four main continents, namely, Gondwana, Baltica, Siberia and Laurentia.

4. Silurian: The fourth Silurian period traces the fishes with bony skeleton. Ancestors of shark and dogfish were found in this period. First land-plant appeared which begin to colonize barren land, and also followed by land animals. Coral reefs expand as well. First millipede fossils and sea scorpions ( Euryptides ) found during this epoch. Another significant feature is Laurentia collides with Baltica and closes Iapetus Sea. The period began about 443 Ma and continued for about 25 my.

Fig:8 – Sea scorpion ( Euryptides ) fossil

5. Devonian: This period shows fish as a dominant aquatic animal, and shows the presence of ancestors of the present day air-breathing lungfish as well as some typical bony fishes. Hence, Devonian is also known as ‗the age of Fishes‘. Oceans were still freshwater and fish migrate from southern hemisphere to North America. Besides a transitional form of life between fish and four-footed land-dwelling vertebrate (amphibian) was found to appear in this age. Spreading of the forest was the other important feature of this epoch and hardwoods began to grow. Also amphibians, evergreens and ferns appear. Present-day Arctic Canada was at the equator. The epoch started by about 419 Ma and persisted for about 60 my.

Fig:9 – an amphibian species

6. Carboniferous : The significant features of Carboniferous period include formation of Gondwanaland and small northern continents, and there had abundant occurrences of fish along with primitive forms of amphibians and of early reptiles. Others include also the appearance of different types of insects, spiders. There had extensive forests of early vascular plants, especially lycopsids, sphenopsids, ferns. This epoch began about 359 Ma and lasted for 60 My.

Two series of development within this epoch, namely Mississippian and Pennsylvanian sub-system, have been ratified in 2000 and internationally approved in the year 2004. The time spans of these series are recorded between 326.4 – 359.2 Ma and 309.9 – 318.1 Ma (GTS 2004) respectively.

The name Mississippian was first coined by an American geologist Alexander Winchell in 1869 referring the rock outcrops along the drainage basin of the Mississippi River. He distinguished these limestone-rich Lower Carboniferous rock layers from the coal-bearing beds of the Upper Carboniferous (or Pennsylvanian). Important features of the Mississippian series include appearance of first seed plants. During this period much of North America is covered by shallow seas and sea life flourishes (including coral, brachiopods , blastoids , and bryozoa ). And also first seed plants appear.

Pennsylvanian Subsystem was named for Pennsylvania, home of some of North America‘s richest coal seams. The name was coined in 1891 by Henry S. Williams for the Upper Carboniferous rock layers of North America. This series showed the initial formation of modern North America. Ice covers the southern hemisphere and coal swamps formed along the equator. Major animal species appeared include lizards, reptiles develop from amphibians. Flying winged insects also appear.

7. Permian: The last of Paleozoic era is Permian. Continents aggregated into Pangaea It is the age of large amphibians and also the land dwelling reptiles which spread across continents. The rise of Appalachians is another significant feature. Owing to volcanic phenomenon in Siberia, there had major mass extinctions (about 90% of Earth‘s species) especially the marine life at end of period. These include most of the species of fishes, trilobites, ammonoids, blastoids, etc. The epoch started approximately about 300 Ma and continued for 48 My.

6.3 THE MESOZOIC ERA (the ‗ Age of Reptiles ‘)

Mesozoic era comprises three periods, Triassic, Jurassic and Cretaceous – each has distinct characters of its own in terms of the development of plate tectonic and of life forms.

Triassic: The first period of Mesozoic, the Triassic, is characterized by the initial separation of continents where Pangea breaks apart and formation of Rocky Mountains and Sierra Nevada. Marine diversity increases; ‗gymnosperms‘ become dominant. Other significant features are the diversification of ‗reptiles‘ including first dinosaurs and first mammals, and crinoids, and modern echinoids. Evidenced of first turtle fossil from this period.

Jurassic : Continents separating, Pangea still breaking apart; North America continues to rotate away from Africa; Dinosaurs flourish -―Golden age of dinosaurs‖ , First birds appear, archaic mammals; ―gymnosperms‖ dominant; evolution of angiosperms; ammonoid radiation; characterized by the ―Mesozoic marine revolution‖.

Cretaceous: Cretaceous being the last period of Mesozoic is characterized by the separation of most continents, continued radiation of dinosaurs, angiosperms appear with increasing diversity. T-Rex develops but number of ammonoids and dinosaur species decline at end of period and also demise of about 25% of all marine life caused by a meteorite impact. Snakes, birds and first primates appear, deciduous trees and grasses common. Mass extinction marks the end of the Mesozoic Era.

6.4 THE CENOZOIC ERA (the ―Age of Mammals‖)

The last and most recent of the geologic time is the Cenozoic Era ( 66.4 to 0.01 Mya), which means ‗new life‘ – the term of which is derived from two Greek roots kainos , (new) and zoic (life). Among others, the two most important features of this era are – i) the rise of the mammals, and ii) appearance of the angiosperm or flowering plants, besides the insects, the newest fish ( teleostei ) or modern birds. This final era is divided into two major periods – Tertiary and Quaternary.

Tertiary Period

The Tertiary Period lasted between 66 – 2.59 Ma (GTS 2012). There had warm and moist climatic condition in the beginning of the period but soon, cooling had lead to an ice age. Major Events of the period include the development of all modern phyla, formation of the current configurations of continents and the rise of mammals. Obviously, there were major fragmentation of two super-continents – the Gondawana of Southern Hemisphere and Laurasia of Northern Hemisphere. Hence, Australia was separated from Antarctica during late Palaeocene, Africa from India (and India collided with Asia), and Greenland from Europe. Life forms developed are the primitive whales, monkeys, cats/dogs, pigs, rhinos, horses, the modern forms of whales, etc. The term Tertiary was introduced first by Giovanni Arduino in 1760 to denote –

i) the youngest of a tripartite division of the Earth’s rocks, such as, the Primitive schists, granites , and basalts that formed the core of the high mountains (of Europe);

ii) the fossiliferous Secondary, or Mesozoic, in northern Italy (predominantly shales and limestones); and

iii) a younger group of fossiliferous sedimentary rocks, the Tertiary rocks, found chiefly at lower elevations.

In 1810 Alexandre Brongniart included all the sedimentary deposits of the Paris Basin in his terrains tertiares , or Tertiary, and soon thereafter all rocks younger than Mesozoic in Western Europe were called Tertiary. The recognition of the Quaternary Period in 1829 by Jules Desnoyers—based on the post-Tertiary deposits of the Seine valley—placed a somewhat different connotation on the term Tertiary, particularly in regard to its upper limits. Quaternary is not a satisfactory name in the hierarchy of stratigraphic nomenclature. The terms Primary and Secondary have been supplanted by Paleozoic and Mesozoic, and Tertiary is being gradually replaced by Paleogene and Neogene as formal period names in scientific literature. Some authorities prefer not to use the term Tertiary and instead divide the time interval encompassed by it into two periods, the Paleogene Period (66.4 to 23.7 million years ago) and the Neogene Period (23.7 to 1.6 million years ago).

Charles Lyell‘s (1833) classification of Tertiary was on the basis of the relative percentages of living species of mollusks to fossil mollusks found in different layers of tertiary rocks. His four-tier division was made mainly from those finds from in West European Basin, such as,

iv. New Pliocene ( later renamed as Pleistocene ) – 90 % of living mollusk,

iii. Pliocene – 1/3 or over 50 % of living mollusk,

ii. Miocene – 20 % of living mollusk,

i. Eocene– 3 % of living mollusk.

Tertiary Era is classified into five epochs namely – from oldest to youngest Paleocene, Eocene, Oligocene, Miocene, and Pliocene.

The earliest epoch, the Paleocene dates back about 66-56 Ma (GTS 2012) with a duration of about ten million years. Palaeocene is defined generally on the basis of fossil flora (that is from non-marine strata) and the term was accepted formally by the United States Geological Survey in 1939. This period witnessed extinction of dinosaurs and the emergence of primates. Primitive lemuroids and tarsioids came into existence along with insectivores. Tropical plants dominate during the epoch. Also seen the appearance of first horses of the size of a cat.

Eocene: Started around 56 Ma and continued about 23 million years, this epoch shows the appearance of modern mammalian orders. Besides, an abundance small primate (prosimians) was noted in this epoch for which the epoch is often referred as the ‗Golden Age‘ of the Prosimians. Emergence of angiosperms with their massive radiation, and appearance of many new species of small plants, trees and shrubs are some of the significant features of this epoch. The Eocene is typified in shallow marine strata of the Paris-London Basin, which interfinger with mammal-bearing beds laid down on adjacent coastal plains. This well-documented correlation between marine and nonmarine faunas in the type area supports a reliable worldwide chronostratigraphy.

Oligocene : No formations of Oligocene age were included in Charles Lyell‘s review of European stratigraphy when he formulated the Eocene and the Miocene in 1833, and, in fact, he used the great difference between the fossils of these two epochs as a useful demonstration of a hitherto unappreciated vastness of geological time. Spanning during 33.9 to 23 Ma (GTS 2012) the Oligocene epoch is characterized by the replacement of tropical and subtropical forests by the temperate deciduous woodland in some parts of the world. Angiosperms continued their expansion throughout the world. Another significant development in life forms is the appearance of the New World monkeys. The ancestors of the Old World monkeys and primitive anthropoid apes like Propliopithecus, Parapithecus etc also appeared in the Old World. Oligocene is divided into two global stages or ages, the Rupelian and the Chattian, which are typified in shallow marine sequences in the North German Plain.

Miocene: The Miocene epoch, that spans the interval between 23.5 and 5.3 Ma, was introduced in 1833 by Sir Charles Lyell for the marine strata representing the time when 40–60 percent of the extinct molluscan species. The Miocene, like all chronostratigraphic units, is framed in a hierarchical series, and its limits are thus defined by its six subordinate stages. The epoch showed divergence of monkeys and apes from their ancestral stock. During its last phase, Dryopithecus , Sivapithecus, Proconsul etc. appeared. Deer, hyenas, giraffes also appeared. Sea whales proliferated and corals and gastropods were plentiful.

Pliocene: Pliocene (5.33 -2.59 Ma ), the last epoch of Cenozoic era was marked by increasingly wide swings in global climates, but without the intense short-term cyclicity of the Pleistocene. During the warm-climate intervals, the winter frost line retreated virtually to the Arctic Circle, and seasonal variation in rainfall was moderate, in contrast to cold winters and summer-dry seasonality during the progressively more intense cold-climate intervals. Significant expansion of ice caps during the cold-climate intervals is indicated by tillites and ice-rafted debris at high latitudes, as early as 3 Ma in Norway and Iceland, and evidence for worldwide lowering of sea level.

This epoch witnessed the appearance of dominant mammalian faunas, like sheep, goat, antelope, cattle, etc. Besides there was rise of higher primates and the forerunners of the present day anthropoid apes also evolved distinctly during this period. Different mountain ranges were formed subsequent to the earthquake, volcanic action, etc.

Quaternary Period

Quaternary refers to the last period of Cenozoic era and is divided into two epochs – the Pleistocene and Holocene. This era begins from 2.59 Ma (GTS 2012) and is continuing still today. The significant events include origin and evolution of modern humans, glaciations and pluviation, and flourishing of humans in the later parts.

Pleistocene epoch ( 2.59 – 0.78 Ma): The term Pleistocene (Gr. Pleistos , meaning ―most‖ and kainos , meaning ―new‖ or ―recent‖) was introduced by Sir Charles Lyell in 1839 to describe marine strata in the Mediterranean region that contain molluscan faunas, the species of which are more than 70 percent living. In the light of present knowledge such a definition would include much of the time now universally assigned to the late Tertiary. In 1846 Forbes used the word Pleistocene to apply to the ‗glacial epoch‘ thus giving a climatic implication – a redefinition to which Lyell agreed in 1873. A definition based on climatic change as evidenced by continental glaciations is almost universally used for Pleistocene in central and northern North America as indicated by the official usage of the U. S. Geological Survey (Wilmarth, 1925: 49).

Although this new, glacial-age definition seemed reasonable at the time, it is now inaccurate to view the Pleistocene as equivalent to the occurrence of glaciations. The reasons for this are twofold. First, full-scale continental glaciations began around one million years ago, well after the start of the Pleistocene at 1.8 million years ago, and not all parts of the Earth were affected at the same time. Second, the existence of pre-Pleistocene glacial events was not known by Lyell or Forbes, but it is now known that glacial conditions existed periodically throughout Earth’s history, even in Precambrian times.

The Pleistocene is a unique epoch because it is the period during which our own species, Homo sapiens , evolved. It is also marked by climatic fluctuations that culminated in widespread continental glaciers and these phenomenons obviously stimulate in human evolution. And many species of vertebrates, especially large mammals, went extinct during the Pleistocene, but much of the modern flora and fauna are survivors from this epoch.

Major evidences, that show that there were Great Ice Ages during the Pleistocene times, include – Moraines and Loesses, Changes in flora and fauna, River terraces, Sea-level Changes and so on.

Glacial cycles were not the only geological and climatic characteristics of the Pleistocene. Volcanic activity was also occurring in the rift valleys of Africa and in western North and South America. In southwestern North America, the Colorado River began to carve out the Grand Canyon. Although the Pleistocene represents a brief portion of geologic time, it includes detailed records of profound changes in climate and landscape.

Holocene epoch: First proposed in the third International Geological Congress 1885, the term Holocene refers to the most recent division of Earth history. Terms like Recent or Postglacial were also used for this epoch until 1967, when the U.S. Geological Survey formally adopted the term ‗Holocene‘ and discontinued the use of ‗Recent‘. The Holocene, which covers the last 11,500 years of Earth history, is an important chronostratigraphic division that follows the Pleistocene Epoch. Significantly, during this epoch most of our modern landscapes and soils evolved. In addition, significant changes in global climate occurred as the Earth moved into a postglacial or interglacial regime. The name and faunal definition of Holocene are consistent with the criteria for Cenozoic epochs proposed by Charles Lyell in 1833, but the internal subdivision of the Holocene and even its traditional boundary have been identified with climatostratigraphic transitions. Important features include – flourishing varied Human culture, extinction of mastodons and the formation of barrier islands and beaches. In many parts of the world witnessed formation of barrier islands and beaches.

Basing on the variations in air-temperature and precipitation regimes, Holocene can be divided into three climatic stages – i) the earliest or the anathermal stage (spanning from 11Ka to 3Ka) which was cooler and mostly wetter than today, ii) the hypsithermal (or altithermal ) stage – ranging between 1000 BCE and ca. 1400 CE, when climate was warmer and mostly drier than today, and iii) the medithermal stage, also known as the Little Ice Age (from 1400 to 1900 CE) that reached a relatively cold, wet-climate minimum ca. 1650 CE. However such a division is not widely accepted, owing to current concerns about ozone depletion and carbon dioxide loading.

Cloud, P. 1972. A working model of the primitive Earth. American Journal of Science. 272: 537-548.
Cloud, P. 1987. Trends, transitions, and events in Cryptozoic history and their calibration: apropos recommendations by the Subcommission on Precambrian Stratigraphy. Precambrian Research, 37: 257-264.
Crook, K.A.W. 1989. Why the Precambrian time-scale should be chronostratigraphic: a response to recommendations by the Subcommittee on Precambrian Stratigraphy. Precambrian Research, 43: 143-150.
Delson, E.; I. Tattersall, J. A.V. Couvering, A. S. Brooks (eds). 2000. Encyclopedia of Human Evolution and Prehistory. New York: Garland Publishing, Inc.
Gradstein, F. M., J. G. Ogg, A. G. Smith, W. Bleeker, and L. J. Lourens. 2004. A new Geologic Time Scale, with special reference to Precambrian and Neogene. Episodes, 27 (2): 83- 100.
Gradstein, F.M., and J.G. Ogg, 2006. Chronostratigraphic data base and visualization; Cenozoic-Mesozoic-Paleozoic integrated stratigraphy and user-generated time scale graphics and charts. Geo Arabia. 11 (3): 181-184.
Gradstein, F.M., and Ogg, J.G., 2004, Geologic time scale 2004 – why, how, and where next! http://www.stratigraphy.org/scale04. pdf, 7 p.
Gradstein, F.M., J.G. Ogg, A.G. Smith, F.P.Agterberg, W.Bleeker, R.A.Cooper, V. Davydov, P. Gibbard, L.A. Hinnov, M.R. House, L.Lourens, H-P.Luterbacher, J. McArthur, M.J. Melchin, L.J.Robb, P.M.Sadler, J. Shergold, M.Villeneuve, B.R.Wardlaw, J. Ali, H. Brinkhuis, F.J. Hilgen, J. Hooker, R.J. Howarth, A.H. Knoll, J. Laskar, S. Monechi, J. Powell, K.A. Plumb, I. Raffi, U. Röhl, A. Sanfilippo, B. Schmitz, N.J. Shackleton, G.A. Shields, H. Strauss, J. Van Dam, J. Veizer, Th. Van Kolfschoten, and D. Wilson. 2004. Geologic Time Scale 2004. Cambridge: Cambridge University Press.
Harland, W.B., A.V. Cox, P. G. Llewellyn, C.A.G. Pickton, A.G. Smith, and R. Walters. 1982. A geologic time scale 1982. London: Cambridge University Press.
Harland, W.B., R.L. Armstrong, A.V.Cox, L.E. Craig, A.G. Smith, and D.G. Smith. 1990. A geologic time scale 1989. London: Cambridge University Press.
http://www.farm9.staticflickr.com/8064/8250087326, dt. 09.8.2015
http://www.lwrw.org/petralona, dt. 09.8.2015
Knoll, A. H, M. Walter, G. Narbonne, and N. Christie-Blick. 2004. ‘The Edicaran Period: A New addition to the Geologic Time Scale’ Submitted on Behalf of the Terminal Proterozoic Subcommission of the International Commission on Stratigraphy.
Knoll, A. H., Walter, M. R., Narbonne, G. M., and Christie-Blick, N. 2006. The Edicaran Period: a new addition to the geologic time scale. Lethaia 39: 13–30. doi:10.1080/00241160500409223.
Knoll, A. H.; M.R. Walter, G. M. Narbonne, N. Christie-Blick. 2004. A New Period for the Geologic Time Scale. Science 305 (5684): 621–622. doi:10.1126/science.1098803.
Noble, W. and I. Davidson. 1997. Human Evolution Language and Mind. (reprint) Cambridge: Cambridge University Press.
Sokolov, B. M. 1952. ‘On the age of the old sedimentary cover of the Russian Platform. Izvestiya Akademii Nauk SSS., Seriya eologicheskaya, 5: 21–31.
Sokolov, B.S. 1997. Essays on the Advent of the Vendian System (in Russian). Moscow: KMK Scientific Press.

Contributions to the Geologic Time Scale

Containing papers given at the Geological Time Scale Symposium in 1976, this volume begins with a review of dating and correlation, and includes papers on the topics of: geochronoloic scales, biochronology, the magnetic polarity time scale, the potassium-argon isotopic dating method, isotopic methods, and worldwide Permian chronostratigraphy, among others.

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Contributions to the Geologic Time Scale Author(s): George V. Cohee, Martin F. Glaessner, Hollis D. Hedberg https://doi.org/10.1306/St6398 ISBN-10: 0891810102 ISBN (electronic): 9781629812007 Publisher: American Association of Petroleum Geologists Published: 1978

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Dating and Correlation, A Review Author(s) D. J. Mclaren D. J. Mclaren Search for other works by this author on: GSW Google Scholar Doi: https://doi.org/10.1306/St6398C1 Abstract Open the PDF Link PDF for Dating and Correlation, A Review in another window Add to Citation Manager
Geochronologic Scales Author(s) W. B. Harland W. B. Harland Search for other works by this author on: GSW Google Scholar Doi: https://doi.org/10.1306/St6398C2 Abstract Open the PDF Link PDF for Geochronologic Scales in another window Add to Citation Manager
Stratotypes and an International Geochronologic Scale Author(s) Hollis D. Hedberg Hollis D. Hedberg Search for other works by this author on: GSW Google Scholar Doi: https://doi.org/10.1306/St6398C3 Abstract Open the PDF Link PDF for Stratotypes and an International Geochronologic Scale in another window Add to Citation Manager
Biochronology Author(s) W. A. Berggren ; W. A. Berggren Search for other works by this author on: GSW Google Scholar J. A. van Couvering J. A. van Couvering Search for other works by this author on: GSW Google Scholar Doi: https://doi.org/10.1306/St6398C4 Abstract Open the PDF Link PDF for Biochronology in another window Add to Citation Manager
The Magnetic Polarity Time Scale: Prospects and Possibilities in Magnetostratigraphy Author(s) M. W. Mcelhinny M. W. Mcelhinny Search for other works by this author on: GSW Google Scholar Doi: https://doi.org/10.1306/St6398C5 Abstract Open the PDF Link PDF for The Magnetic Polarity Time Scale: Prospects and Possibilities in Magnetostratigraphy in another window Add to Citation Manager
Subcommission on Geochronology: Convention on the Use of Decay Constants in Geochronology and Cosmochronology Author(s) R. H. Steiger ; R. H. Steiger Search for other works by this author on: GSW Google Scholar E. Jäger E. Jäger Search for other works by this author on: GSW Google Scholar Doi: https://doi.org/10.1306/St6398C6 Abstract Open the PDF Link PDF for Subcommission on Geochronology: Convention on the Use of Decay Constants in Geochronology and Cosmochronology in another window Add to Citation Manager
Pre-Cenozoic Phanerozoic Time Scale—Computer File of Critical Dates and Consequences of New and In-Progress Decay-Constant Revisions Author(s) Richard Lee Armstrong Richard Lee Armstrong Search for other works by this author on: GSW Google Scholar Doi: https://doi.org/10.1306/St6398C7 Abstract Open the PDF Link PDF for Pre-Cenozoic Phanerozoic Time Scale—Computer File of Critical Dates and Consequences of New and In-Progress Decay-Constant Revisions in another window Add to Citation Manager
Applicability of the Rubidium-Strontium Method to Shales and Related Rocks Author(s) Umberto G. Cordani ; Umberto G. Cordani Search for other works by this author on: GSW Google Scholar Koji Kawashita ; Koji Kawashita Search for other works by this author on: GSW Google Scholar Antonio Thomaz Filho Antonio Thomaz Filho Search for other works by this author on: GSW Google Scholar Doi: https://doi.org/10.1306/St6398C8 Abstract Open the PDF Link PDF for Applicability of the Rubidium-Strontium Method to Shales and Related Rocks in another window Add to Citation Manager
Potassium-Argon Isotopic Dating Method and Its Application to Physical Time-Scale Studies Author(s) Ian McDougall Ian McDougall Search for other works by this author on: GSW Google Scholar Doi: https://doi.org/10.1306/St6398C9 Abstract Open the PDF Link PDF for Potassium-Argon Isotopic Dating Method and Its Application to Physical Time-Scale Studies in another window Add to Citation Manager
Results of Dating Cretaceous, Paleogene Sediments, Europe Author(s) G. S. Odin G. S. Odin Search for other works by this author on: GSW Google Scholar Doi: https://doi.org/10.1306/St6398C10 Abstract Open the PDF Link PDF for Results of Dating Cretaceous, Paleogene Sediments, Europe in another window Add to Citation Manager
Isotopic Ages and Stratigraphic Control of Mesozoic Igneous Rocks in Japan 1 Author(s) Ken Shibata ; Ken Shibata Search for other works by this author on: GSW Google Scholar Tatsuro Matsumoto ; Tatsuro Matsumoto Search for other works by this author on: GSW Google Scholar Takeru Yanagi ; Takeru Yanagi Search for other works by this author on: GSW Google Scholar Reiko Hamamoto Reiko Hamamoto Search for other works by this author on: GSW Google Scholar Doi: https://doi.org/10.1306/St6398C11 Abstract Open the PDF Link PDF for Isotopic Ages and Stratigraphic Control of Mesozoic Igneous Rocks in Japan<a href="javascript:;" reveal-id="ch11fn1" data-open="ch11fn1" class="link link-ref link-reveal xref-fn js-xref-fn split-view-modal">1</a> in another window Add to Citation Manager
Isotopic Methods in Quaternary Geology 1 Author(s) Vladimir Šibrava Vladimir Šibrava Search for other works by this author on: GSW Google Scholar Doi: https://doi.org/10.1306/St6398C12 Abstract Open the PDF Link PDF for Isotopic Methods in Quaternary Geology<a href="javascript:;" reveal-id="ch12fn1" data-open="ch12fn1" class="link link-ref link-reveal xref-fn js-xref-fn split-view-modal">1</a> in another window Add to Citation Manager
Status of the Boundary between Pliocene and Pleistocene Author(s) K. V. Nikiforova K. V. Nikiforova Search for other works by this author on: GSW Google Scholar Doi: https://doi.org/10.1306/St6398C13 Abstract Open the PDF Link PDF for Status of the Boundary between Pliocene and Pleistocene in another window Add to Citation Manager
A Radiometric Time Scale for the Neogene of the Paratethys Region Author(s) Dionyz Vass ; Dionyz Vass Search for other works by this author on: GSW Google Scholar Gevorg P. Bagdasarjan Gevorg P. Bagdasarjan Search for other works by this author on: GSW Google Scholar Doi: https://doi.org/10.1306/St6398C14 Abstract Open the PDF Link PDF for A Radiometric Time Scale for the Neogene of the Paratethys Region in another window Add to Citation Manager
On Dating of the Paleogene Author(s) M. Rubinstein ; M. Rubinstein Search for other works by this author on: GSW Google Scholar L. Gabunia L. Gabunia Search for other works by this author on: GSW Google Scholar Doi: https://doi.org/10.1306/St6398C15 Abstract Open the PDF Link PDF for On Dating of the Paleogene in another window Add to Citation Manager
A New Paleogene Numerical Time Scale Author(s) J. Hardenbol ; J. Hardenbol Search for other works by this author on: GSW Google Scholar W. A. Berggren W. A. Berggren Search for other works by this author on: GSW Google Scholar Doi: https://doi.org/10.1306/St6398C16 Abstract Open the PDF Link PDF for A New Paleogene Numerical Time Scale in another window Add to Citation Manager
Critical Review of Isotopic Dates in Relation to Paleogene Stratotypes Author(s) Charles Pomerol Charles Pomerol Search for other works by this author on: GSW Google Scholar Doi: https://doi.org/10.1306/St6398C17 Abstract Open the PDF Link PDF for Critical Review of Isotopic Dates in Relation to Paleogene Stratotypes in another window Add to Citation Manager
Isotopic Dates for a Paleogene Time Scale Author(s) G. S. Odin G. S. Odin Search for other works by this author on: GSW Google Scholar Doi: https://doi.org/10.1306/St6398C18 Abstract Open the PDF Link PDF for Isotopic Dates for a Paleogene Time Scale in another window Add to Citation Manager
Cretaceous Time Scale from North America Author(s) Marvin A. Lanphere ; Marvin A. Lanphere Search for other works by this author on: GSW Google Scholar David L. Jones David L. Jones Search for other works by this author on: GSW Google Scholar Doi: https://doi.org/10.1306/St6398C19 Abstract Open the PDF Link PDF for Cretaceous Time Scale from North America in another window Add to Citation Manager
A Cretaceous Time Scale Author(s) J. E. van Hinte J. E. van Hinte Search for other works by this author on: GSW Google Scholar Doi: https://doi.org/10.1306/St6398C20 Abstract Open the PDF Link PDF for A Cretaceous Time Scale in another window Add to Citation Manager
A Jurassic Time Scale Author(s) J. E. van Hinte J. E. van Hinte Search for other works by this author on: GSW Google Scholar Doi: https://doi.org/10.1306/St6398C21 Abstract Open the PDF Link PDF for A Jurassic Time Scale in another window Add to Citation Manager
Chronostratigraphy for the World Permian Author(s) J. B. Waterhouse J. B. Waterhouse Search for other works by this author on: GSW Google Scholar Doi: https://doi.org/10.1306/St6398C22 Abstract Open the PDF Link PDF for Chronostratigraphy for the World Permian in another window Add to Citation Manager
Report on Isotopic Dating of Rocks in the Carboniferous System Author(s) A. Bouroz A. Bouroz Search for other works by this author on: GSW Google Scholar Doi: https://doi.org/10.1306/St6398C23 Abstract Open the PDF Link PDF for Report on Isotopic Dating of Rocks in the Carboniferous System in another window Add to Citation Manager
The Mississippian-Pennsylvanian Boundary Author(s) Mackenzie Gordon, Jr. ; Mackenzie Gordon, Jr. Search for other works by this author on: GSW Google Scholar B. L. Mamet B. L. Mamet Search for other works by this author on: GSW Google Scholar Doi: https://doi.org/10.1306/St6398C24 Abstract Open the PDF Link PDF for The Mississippian-Pennsylvanian Boundary in another window Add to Citation Manager
Devonian Author(s) Willi Ziegler Willi Ziegler Search for other works by this author on: GSW Google Scholar Doi: https://doi.org/10.1306/St6398C25 Abstract Open the PDF Link PDF for Devonian in another window Add to Citation Manager
The Silurian System Author(s) Nils Spjeldnaes Nils Spjeldnaes Search for other works by this author on: GSW Google Scholar Doi: https://doi.org/10.1306/St6398C26 Abstract Open the PDF Link PDF for The Silurian System in another window Add to Citation Manager
Ordovician Geochronology Author(s) Reuben J. Ross, Jr. ; Reuben J. Ross, Jr. Search for other works by this author on: GSW Google Scholar Charles W. Naeser ; Charles W. Naeser Search for other works by this author on: GSW Google Scholar Richard S. Lambert Richard S. Lambert Search for other works by this author on: GSW Google Scholar Doi: https://doi.org/10.1306/St6398C27 Abstract Open the PDF Link PDF for Ordovician Geochronology in another window Add to Citation Manager
The Cambrian System Author(s) J. W. Cowie ; J. W. Cowie Search for other works by this author on: GSW Google Scholar S. J. Cribb S. J. Cribb Search for other works by this author on: GSW Google Scholar Doi: https://doi.org/10.1306/St6398C28 Abstract Open the PDF Link PDF for The Cambrian System in another window Add to Citation Manager
Numerical Correlation of Middle and Upper Precambrian Sediments Author(s) Michel G. Bonhomme Michel G. Bonhomme Search for other works by this author on: GSW Google Scholar Doi: https://doi.org/10.1306/St6398C29 Abstract Open the PDF Link PDF for Numerical Correlation of Middle and Upper Precambrian Sediments in another window Add to Citation Manager
Aspects of the Revised South African Stratigraphic Classification and a Proposal for the Chronostratigraphic Subdivision of the Precambrian Author(s) L. E. Kent ; L. E. Kent Search for other works by this author on: GSW Google Scholar P. J. Hugo P. J. Hugo Search for other works by this author on: GSW Google Scholar Doi: https://doi.org/10.1306/St6398C30 Abstract Open the PDF Link PDF for Aspects of the Revised South African Stratigraphic Classification and a Proposal for the Chronostratigraphic Subdivision of the Precambrian in another window Add to Citation Manager
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Earthquake shakes U.S. East Coast

An earthquake struck the East Coast of the United States on Friday morning, according to the U.S. Geological Survey, causing buildings to shake and rattling nerves from Maryland to Maine.

The USGS measured the quake as a 4.8 temblor with its epicenter near Lebanon, New Jersey. It struck a little before 10:30 a.m. ET. An aftershock of magnitude-4.0 hit right around 6 p.m. ET.

The morning earthquake was the strongest recorded in the Northeast in more than a decade, according to USGS records .

There were no immediate reports of major destruction or any fatalities. Local and regional officials from cities in the earthquake zone said inspections had been launched to ensure that buildings, bridges and other infrastructure were not damaged.

Follow here for live updates on the earthquake.

James Pittinger, mayor of Lebanon, New Jersey, called the earthquake “the craziest thing I’ve ever experienced.” In an interview with MSNBC , he said he had not received reports of any significant damage so far, but added that the shaking caused his dog to run for cover and objects to fall off his shelves.

While a 4.8-magnitude temblor is not considered a major earthquake, even minor shaking can cause damage on the East Coast, which does not take similar precautions as other earthquake hot spots around the world.

New York Gov. Kathy Hochul said the quake was felt across the state.

“My team is assessing impacts and any damage that may have occurred, and we will update the public throughout the day,” she wrote on X .

New York City Mayor Eric Adams said in an afternoon news briefing that no major injuries or impacts to infrastructure were reported, and that people in the city should “go about their normal day.”

Ground stops were temporarily issued at Newark Liberty International Airport in New Jersey and John F. Kennedy International Airport in New York City, according to the Federal Aviation Administration's website. Flight disruptions at the Newark airport continued into the afternoon .

The Port Authority Transit Corp., which operates a rapid transit route between Pennsylvania and New Jersey, suspended service in the aftermath of the quake.

“Crews will inspect the integrity of the line out of an abundance of caution,” PATCO said in an update on X . “Once inspection is complete, service will resume. No timeframe. Updates to follow.”

New York’s Metropolitan Transportation Authority said that there had been no impact to its service but that teams will be inspecting train lines. New Jersey Transit alerted riders of 20-minute delays due to bridge inspections following the earthquake.

While earthquakes in the northeast U.S. are rare, Buffalo, New York, was struck by a 3.8-magnitude quake in February 2023 — the strongest recorded in the area in 40 years.

A 4.1-magnitude earthquake struck the tri-state area in 2017, centered near Little Creek, Delaware, according to the U.S. Geological Survey . And before that, a 5.8-magnitude quake shook central Virginia in 2011, and was felt across much of the East Coast, forcing hundreds of thousands people to evacuate buildings in New York, Washington and other cities.

New Jersey Gov. Phil Murphy said in a post on X that the state has activated its emergency operations center and asked the public not to call 911 unless they are experiencing an emergency.

Frederik J. Simons, a professor of geosciences at Princeton University, told NBC News that the earthquake occurred on a shallow fault system in New Jersey and lasted about 35 seconds.

“The shallower or the closer it is, the more we feel it as humans,” he said.

The quake originated at a depth of less than 3 miles, according to the USGS .

Earthquakes on the East Coast can be felt at a great distance and can cause more pronounced shaking in comparison to those on the West Coast because rocks in the region are often older, harder and more dense.

“These are competent rocks that transmit energy well,” Simons said.

The earthquake ruptured within a fault zone known as the Ramapo system, Simons said. It’s a zone in relatively ancient rock that contains old faults and cracks from ancient tectonic processes. These old faults slowly accumulate stress and occasionally something slips, Simons said.

“There are cracks in it and now and then a little motion accumulates, the stress keeps growing, at very slow rates,” he said. “It’s like an old house creaking and groaning.”

Simons said this was one of the largest earthquakes in New Jersey in recent history. The last notable one was a magnitude-3.1 temblor in Freehold Township in September 2020.

“I’m on campus at Princeton University for the biggest one I’ve felt in a lifetime,” he said. “This shaking was violent, strong and long.”

Some videos captured the moment of the earthquake, including one from a coffee shop in New Jersey.

The East Coast quake struck two days after a powerful 7.4-magnitude temblor shook the island of Taiwan, killing at least 12 people and injuring more than 1,000 others. The two incidents are not thought to be related, said Dara Goldberg, a USGS geophysicist.

“We’re much too far of a distance for the stress on the fault of Taiwan to affect New York,” she said.

Denise Chow is a reporter for NBC News Science focused on general science and climate change.

Evan Bush is a science reporter for NBC News. He can be reached at [email protected].

Map: 4.8-Magnitude Earthquake Strikes New Jersey

By William B. Davis , Madison Dong , Judson Jones , John Keefe , Bea Malsky and Lazaro Gamio

Shake intensity

A light, 4.8-magnitude earthquake struck in New Jersey on Friday, according to the United States Geological Survey. The quake was felt across the New York City metropolitan area, and from Philadelphia to Boston.

The temblor happened at 10:23 a.m. Eastern about 4 miles north of Whitehouse Station, N.J., data from the agency shows.

As seismologists review available data, they may revise the earthquake's reported magnitude. Additional information collected about the earthquake may also prompt U.S.G.S. scientists to update the shake-severity map.

Aftershocks in the region

At 5:59 p.m. Eastern on Friday, a light aftershock with a magnitude of 3.8 struck near Gladstone, New Jersey, according to U.S.G.S. (The agency initially gave the quake a preliminary magnitude of 4.0.)

An aftershock is usually a smaller earthquake that follows a larger one in the same general area. Aftershocks are typically minor adjustments along the portion of a fault that slipped at the time of the initial earthquake.

Quakes and aftershocks within 100 miles

Aftershocks can occur days, weeks or even years after the first earthquake. These events can be of equal or larger magnitude to the initial earthquake, and they can continue to affect already damaged locations.

How this quake compares

The U.S.G.S. has logged 188 earthquakes with a magnitude of 2.5 or greater within a 250-mile radius of New York City since 1957. In that timeframe, only seven have had a magnitude at or above 4.5. Today’s quake had the third-highest magnitude in the available data.

Today’s earthquake

Magnitude 4.8

250-mile radius

from New York City

Source: U. S.G.S.

By Lazaro Gamio

Source: United States Geological Survey | Notes: Shaking categories are based on the Modified Mercalli Intensity scale. When aftershock data is available, the corresponding maps and charts include earthquakes within 100 miles and seven days of the initial quake. All times above are Eastern. Shake data is as of Friday, April 5 at 10:44 a.m. Eastern. Aftershocks data is as of Friday, April 12 at 1:38 a.m. Eastern.

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Watch CBS News

Earthquake maps show where seismic activity shook the Northeast today

By Lucia Suarez Sang

Updated on: April 5, 2024 / 7:51 PM EDT / CBS News

Residents across the Northeast were rattled by a 4.8 magnitude earthquake that shook the densely populated New York City metropolitan area and much of the surrounding region on Friday morning. The U.S. Geological Survey was quick to release maps showing the spot where the quake was centered, in New Jersey, and the area where it was felt.

The USGS reported the quake occurred about 7 miles north of Whitehouse Station, New Jersey. It indicated that the quake might have been felt by more than 42 million people. There were several aftershocks later in the day, including one with a magnitude of 4.0.

Map shows area affected by earthquake centered in New Jersey

People in Baltimore , Philadelphia , New Jersey, Connecticut, Boston and other areas of the Northeast reported shaking. Tremors lasting for several seconds were felt over 200 miles away near the Massachusetts-New Hampshire border.

The map below shows the seismic intensity of the earthquake. The map, which is mostly a lighter shade of blue, shows that the intensity was light to weak, depending on the distance from the epicenter.

Another map released by the European-Mediterranean Seismological Centre on X, formerly Twitter, highlights the eyewitness reports of shaking and possible damage levels during the seismic event.

#Earthquake 18 mi W of #Plainfield (New Jersey) 23 min ago (local time 10:23:20). Updated map - Colored dots represent local shaking & damage level reported by eyewitnesses. Share your experience via: 📱 https://t.co/IbUfG7TFOL 🌐 https://t.co/wErQf69jIn pic.twitter.com/jBjVw1ngAD — EMSC (@LastQuake) April 5, 2024

New York Gov. Kathy Hochul and New York City Mayor Eric Adams have been briefed on the quake.

"We're taking this extremely seriously and here's why: There's always the possibility of aftershocks. We have not felt a magnitude of this earthquake since about 2011," Hochul said.

People across the region were startled by the rumbling of the quake. One New York City resident told CBS New York's Elijah Westbrook, "I was laying in my bed, and my whole apartment building started shaking. I started freaking out,"

It's not the first time the East Coast and New York City have been hit by an earthquake.

A 5.0 quake was measured in New York City in 1884.

The shaking stirred memories of the Aug. 23, 2011, earthquake that jolted tens of millions of people from Georgia to Canada. Registering magnitude 5.8, it was the strongest quake to hit the East Coast since World War II. The epicenter was in Virginia.

That earthquake left cracks in the Washington Monument, spurred the evacuation of the White House and Capitol and rattled New Yorkers three weeks before the 10th anniversary of the Sept. 11 terror attacks.

New England
Connecticut
Earthquakes
United States Geological Survey
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Lucia Suarez Sang is an associate managing editor at cbsnews.com. Previously, Lucia was the director of digital content at FOX61 News in Connecticut and has previously written for outlets including FoxNews.com, Fox News Latino and the Rutland Herald.

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Time 2024-04-02 23:58:11 UTC Contributed by US 4 ; Moment Tensor Fault Plane Solution Contributed by US 4 ; Tsunami U.S. Tsunami Warning System . To view any current tsunami advisories for this and other events please visit https://www.tsunami.gov. NOAA ; View Nearby Seismicity Time Range ± Three Weeks Search Radius 250.0 km Magnitude Range ...

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15.8: Geologic Time Scale

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3 Geologic Time: From an Early Geologic Time Scale

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The Four Eras of the Geologic Time Scale

Precambrian Time: 4.6 billion to 542 Million Years Ago

Paleozoic Era: 542 Million to 250 Million Years Ago

Mesozoic Era: 250 Million to 65 Million Years Ago

Cenozoic Era: 65 Million Years Ago to the Present

The Importance of the Geologic Time Scale: A Guide for Geoscientists

What is the geologic time scale?

What is the significance of the geologic time scale?

Division of the geologic time scale

Example of division of the geologic time scale

General structure of the geologic time scale

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Geological Time Scale of Earth – Geography Notes

Division of Geological Time Scale

Archean Eon

Proterozoic Eon

Phanerozoic Eon

The Phanerozoic eon is divided into three eras:

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Earthquake shakes U.S. East Coast

Map: 4.8-Magnitude Earthquake Strikes New Jersey

Shake intensity

Aftershocks in the region

Quakes and aftershocks within 100 miles

How this quake compares