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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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How many years is a “long time”? We often express time in hours or days, and 10 or 20 years certainly feels like a long time. Imagine if you needed to think about one million, 100 million, or even several billion years. These exceptional lengths of time seem unbelievable, but they are exactly the spans of times that scientists use to describe the Earth.

The Earth is 4 1 ⁄ 2 billion years old. That’s 4,500,000,000 years! Have places like the Grand Canyon and the Mississippi River been around for all of those years, or were they formed more recently? When did the giant Rocky Mountains form and when did dinosaurs walk the Earth? To answer these questions, you have to think about times that were millions or billions of years ago.

Historical geologists are scientists who study the Earth’s past. They study clues left on the Earth to learn two main things: the order in which events happened on Earth, and how long it took for those events to happen. For example, they have learned that the Mississippi River formed many millions of years after the Grand Canyon began forming. They have also concluded that dinosaurs lived on the Earth for about 200 million years.

Scientists have put together the geologic time scale to describe the order and duration of major events on Earth for the last 4 1 ⁄ 2 billion years. Some examples of events listed on the geologic time scale include the first appearance of plant life on Earth, the first appearance of animals on Earth, the formation of Earth’s mountains, and the extinction of the dinosaurs.

You will learn about some of the scientific principles that historical geologists use to describe Earth’s past. You will also learn some of the clues that scientists use to learn about the past and shows you what the geologic time scale looks like.

Evaluating Prior Knowledge

Before you work through this lesson, think about the following questions. Be sure that you can answer each one. They will help you better understand this lesson.

What is a fossil and how does a fossil form?
How does a sedimentary rock form?
In what types of locations do sedimentary rocks form?
How do you determine the relative and absolute ages of rock layers?

Geologic Time

The first principle you need to understand about geologic time is that the laws of nature are always the same. This means that the laws describing how things work are the same today as they were billions of years ago. For example, water freezes at 0°C. This law has always been true and always will be true. Knowing the natural laws helps you think about Earth’s past, because it gives you clues about how things happened very long ago. It means that we can use present-day processes to interpret the past. Imagine you find fossils of sea animals in a rock. The laws of nature say that sea animals must live in the sea. That law has never changed, so the rock must have formed near the sea. The rock may be millions of years old, but the fossils in it are a clue for us today about how it formed.

Now imagine that you find that same rock with fossils of a sea animal in a place that is very dry and nowhere near the sea. How could that be? Remember that the laws of nature never change. Therefore, the fossil means that the rock definitely formed by the sea. This tells you that even though the area is now dry, it must have once been underwater. Clues like this have helped scientists learn that Earth’s surface features have changed many times. Spots that were once covered by warm seas may now be cool and dry. Places that now have tall mountains may have once been low, flat ground. These kinds of changes take place over many millions of years, but they are still slowly going on today. The place where you live right now may look very different in the far future.

Relative and Absolute Age Dating of Rocks

The clues in rocks help scientists put together a picture of how places on Earth have changed. Scientists noticed in the 1700s and 1800s that similar layers of sedimentary rocks all over the world contain similar fossils. They used relative dating to order the rock layers from oldest to youngest. In the process of relative dating, scientists do not determine the exact age of a fossil but do learn which ones are older or younger than others. They saw that the fossils in older rocks are different from the fossils in younger rocks. For example, older rock layers contain only reptile fossils, but younger rock layers may also contain mammal fossils.

Scientists divided Earth’s history into several chunks of time when the fossils showed similar things living on the Earth. They gave each chunk of time a name to help them keep track of how Earth has changed. For example, one chunk of time when many dinosaurs lived is called the Jurassic. We find fossils of Earth’s first green plants from the chunk of time named the Ordovician. Many of the scientists who first assigned names to times in Earth’s history were from Europe. As a result, many of the names they used came from towns or other local places where they studied in Europe.

Ordering rock layers from oldest to youngest was a first step in creating the geologic time scale. It showed the order in which life on Earth changed. It also showed us how certain areas changed over time in regard to climate or type of environment. However, the early geologic time scale only showed the order of events. It did not show the actual years that events happened. With the discovery of radioactivity in the late 1800s, scientists were able to measure the exact age in years of different rocks. Measuring the amounts of radioactive elements in rocks let scientists use absolute dating to give ages to each chunk of time on the geologic time scale. For example, they are now able to state that the Jurassic began about 200 million years ago and that it lasted for about 55 million years.

Geologic Time Scale

Today, the geologic time scale is divided into major chunks of time called eons . Eons may be further divided into smaller chunks called eras, and each era is divided into periods . Figure 12.1 shows you what the geologic time scale looks like. We now live in the Phanerozoic eon, the Cenozoic era, and the Quarternary period. Sometimes, periods are further divided into epochs, but they are usually just named “early” or “late”, for example, “late Jurassic”, or “early Cretaceous”. Note that chunks of geologic time are not divided into equal numbers of years. Instead, they are divided into blocks of time when the fossil record shows that there were similar organisms on Earth.

One of the first scientists to understand geologic time was James Hutton. In the late 1700s, he traveled around Great Britain and studied sedimentary rocks and their fossils. He believed that the same processes that work on Earth today formed the rocks and fossils from the past. He knew that these processes take a very long time, so the rocks must have formed over millions of years. Before Hutton, most people believed the Earth was only several thousand years old. His work helped us understand that the laws of nature never change and that the Earth is very old. He is sometimes called the “father of geology”.

The geologic time scale is often shown with illustrations of how life on Earth has changed. It sometimes includes major events on Earth, too, such as the formation of the major mountains or the extinction of the dinosaurs. Figure 12.2 shows you a different way of looking at the geologic time scale. It shows how Earth’s environment and life forms have changed.

Figure 12.2 : A different way of looking at the geologic time scale.

Lesson Summary

The Earth is very old, and the study of Earth’s past requires us to think about times that were millions or even billions of years ago. Scientists use the geologic time scale to illustrate the order in which events on Earth have happened.
The geologic time scale was developed after scientists observed changes in the fossils going from oldest to youngest sedimentary rocks. They used relative dating to divide Earth’s past in several chunks of time when similar organisms were on Earth.
Later, scientists used absolute dating to determine the actual number of years ago that events happened. The geologic time scale is divided into eons, eras, periods, and epochs.

Review Questions

How old is the Earth?
Why did early geologic time scales not include the number of years ago that events happened?
Dinosaurs went extinct about 66 million years ago. Which period of geologic time was the last in which dinosaurs lived?
Can scientists use the same principles they use to study Earth’s history to also study the history of other planets?
Suppose you are hiking in the mountains of Utah and find a fossil of an animal that lived on the ocean floor. You learn that the rock that holds the fossil is from the Mississippian period. What was the environment like during the Mississippian in Utah?
Why are sedimentary rocks more useful than metamorphic or igneous rocks in establishing the relative ages of rock?
Which is likely to be more frequently found in rocks: fossils of very old sea creatures or very old land creatures?

Points to Consider

How did life on Earth change from one period of geologic time to the next?
When did life first appear on Earth?
What conditions were necessary on Earth for living things to survive?
Provided by : Wikibooks. Located at : http://en.wikibooks.org/wiki/High_School_Earth_Science/Geologic_Time_Scale . License : CC BY-SA: Attribution-ShareAlike

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Song of the Earth: Understanding Geology and Why It Matters

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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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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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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
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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

Geologic Time Scale Estimation

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Felix M. Gradstein 7 &
Frits P. Agterberg 8

Part of the book series: Encyclopedia of Earth Sciences Series ((EESS))

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The Geologic Time Scale (GTS) is the framework for deciphering and understanding the history of our planet. The steady increase in data, development of better methods and new procedures for actual dating and scaling of the rocks on Earth, and a refined relative scale with more defined units pose challenges to the methodology employed to calculate the GTS. This review explains the qualitative and quantitative methods used in GTS2020 with special emphasis on cubic splining. Relative to its ancestor GTS2012, the qualitative and quantitative methodology for GTS2020 is improved, uncertainty reduced, and stratigraphic resolution increased.

Introduction

The Geologic Time Scale (GTS) is the framework for deciphering and understanding the long and complex history of our planet, Earth. As Arthur Holmes, the father of the Geologic Time Scale, once wrote (Holmes 1965 , p. 148): “To place all the scattered pages of earth history in their proper chronological order is by no means an easy...

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Founding Member and Past Chair, Geologic Time Scale Foundation, Emeritus Natural History Museum, University of Oslo, Oslo, Norway

Felix M. Gradstein

Geomathematics Section, Geological Survey of Canada, Ottawa, ON, Canada

Frits P. Agterberg

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System Science & Informatics Unit, Indian Statistical Institute- Bangalore Centre, Bangalore, India

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Insititue of Earth Sciences, China University of Geosciences, Beijing, China

Qiuming Cheng

School of Natural and Built Environment, Queen's University Belfast, Belfast, UK

Jennifer McKinley

Canada Geological Survey, Ottawa, ON, Canada

Frits Agterberg

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Gradstein, F.M., Agterberg, F.P. (2022). Geologic Time Scale Estimation. In: Daya Sagar, B., Cheng, Q., McKinley, J., Agterberg, F. (eds) Encyclopedia of Mathematical Geosciences. Encyclopedia of Earth Sciences Series. Springer, Cham. https://doi.org/10.1007/978-3-030-26050-7_409-1

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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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Earth Science Week Classroom Activities

Geologic time scale analogy, activity source:.

Ritger, S.D. and R.H. Cummins. 1991. Using student-created metaphors to comprehend geologic time. Journal of Geological Education. 9:9-11.

To introduce students to the vastness of [geologic time](/content/geological- time-scale) and the concept of scale .

Unraveling time and the Earth’s biologic history are arguably geology’s most important contributions to humanity. Yet it is very difficult for humans to appreciate time beyond that of one or two generations, much less hundreds, thousands, millions and billions of years. Perhaps we can only hope that students catch glimpses of our rich geologic heritage, particularly when most of our teaching is done in a classroom and not in a field setting. This exercise begins to make time more “three dimensional” and most importantly, students gain a better appreciation for geologic time and our Earth’s history.

Instructions

To better understand the concept of geologic time, have students produce a time-scale metaphor to share with the class that is true to scale and reflects some of the important events in the history of the Earth (see list on the following page). Write an essay that: (1) discusses why you chose the metaphor you used; (2) shows your math calculations; and (3) discusses what you learned from this exercise including your perspective of where humans fit in the grand scheme of things. Have fun! Be creative! No metaphor is too silly, as long as your math is correct and your choice has meaning to you.

The method used to determine a metaphor value true-to-scale will be similar for all metaphors. Units in the metaphor model can be in time, distance, volume, mass, etc. depending upon what type of metaphor you choose to work with. The general equation used to generate numbers in your metaphor which will be true to scale is:

For example, suppose your metaphor uses distance. Remember, the use of time, volume, or mass in your metaphor would be just dandy. Since we are using a distance metaphor as an example here, a football field with a length of 100 yards will do just fine. To find at what distance along the football field, for example, the “first oxygen” yard mark would be, you would set up the ratio shown below:

So taking the math one step further gives you:

(2.01 x 109 years)(100 yards) = (X yards)(4.6 x 109 years)

Solving the ratio (for X) will tell you that the “first oxygen” location on the football field would be 43.7 yards away from the goal line of your choice! Determining the location of the other important dates in the history of the Earth is up to you.

Some Important Dates in the History of the Earth

Earth science week connections, discover the earth sciences.

Discuss the age of the Earth’s crust at different locations (i.e. ocean floor, continents, etc.) Is it older in some places and younger in others? What does this tell you about how the Earth’s crust has changed over the last billion years? Discuss plate tectonics.

Geoscientists

Invite a paleontologist to discuss our geologic history.

Stewardship

The time of human life on Earth is incredibly short when compared to Earth’s vast history, yet during our short existence we have permanently altered our environment. Discuss the implications of the environmental crisis as it exists in the context of Earth history.

Earth Science is all around you

How old are the rocks in your state? Look at geologic maps to examine the history of your area.

Newly emerged Oleander Butterfly Euploea core drying wings

Australian Environmental Education

For all your environmental education needs

The Geologic Timescale

The geologic time scale is a system of chronological dating based on the rock record. It classifies geological layers to describe the timing and relationships of events in geologic history. Over hundreds to thousands of millions of years, continents, oceans and mountain ranges have moved both vertically and horizontally. Areas that were once deep oceans hundreds of millions of years ago are now mountainous or desert regions.

Other subdivisions reflect the evolution of life; the Archean and Proterozoic are both eons, the Palaeozoic, Mesozoic and Cenozoic are eras of the Phanerozoic eon. The three million year Quaternary period, the time of recognizable humans, is too small to be visible at this scale.

Discover the history of Geologic time

Stenos Law of Stratigraphy

Nicolaus Steno was a 17th-century Danish geologist. His laws of stratigraphy describe the patterns in which rock layers are deposited.

Index fossils

Index fossils are fossils used to define and identify geologic periods. Good examples have a defined time period, wide geographic distribution, abundant and fossilize well.

Linked to the relative time scale are examples of index fossils, the forms of life which existed during limited periods of geologic time and thus are used as guides to the age of the rocks in which they are preserved.

Find out more about different time periods

The Ediacaran Period is an interval of geological time ranging 635 to 541 million years ago. During this time there was immense geological and biological change. There was a transition from a life largely dominated by microscopic organisms to a world swarming with animals.

There was a vast change in the variety of life on earth during the Cambrian 541 – 485 million years ago. The Cambrian saw the expansion and diversification of multicellular life. The rapid diversification of life forms in the Cambrian is known as the Cambrian explosion. During this time we see the first representatives of all modern animal groups.

Life flourished in the Ordovician 485 – 444 million years ago with molluscs and arthropods dominating the oceans. This was a period of high diversification called the Ordovician radiation. The early vertebrates evolved during this time.

The Devonian Period 419 to 359 million years ago is sometimes called the “Age of Fishes” because of the amazing diversity and abundance of fish species. An ocean covered approximately 85 percent of the Devonian globe and the climate is thought to have been warm.

The Triassic Period was the first period of the Mesozoic Era and occurred between 251 million and 199 million years ago. It followed the great mass extinction at the end of the Permian Period and was a time when life outside of the oceans began to diversify.

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Geologic Time Scale : Divisions, Periods and Eons » Geology Science
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 ...
Geologic time
The geologic time scale is the "calendar" for events in Earth history. It subdivides all time into named units of abstract time called—in descending order of duration— eons, eras, periods, epochs, and ages.The enumeration of those geologic time units is based on stratigraphy, which is the correlation and classification of rock strata. The fossil forms that occur in the rocks, however ...
7.4: The Geological Time Scale
Time scale history. William Smith used the principle of faunal succession and correlation to great effect in his monumental solo project to create a geological map of England and Wales, published in 1815.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 ...
PDF The Geological Society of America Geologic Time Scale
Over the past 100 years, the confl uence of process-based geo-logical thought with observed and approxi-mated geologic rates has led to coherent and quantitatively robust estimates of geologic time scales, reducing many uncertainties to the 0.1% level. †E-mail: [email protected].
Welcome to Understanding Geologic Time
Learn how to understand geologic time, the evidence for Earth's history, and the geologic time scale with this web-based module from UCMP.
[PDF] On the Geologic Time Scale
This report summarizes the international divisions and ages in the Geologic Time Scale, published in 2012 (GTS2012). Since 2004, when GTS2004 was detailed, major developments have taken place that directly bear and have considerable impact on the intricate science of geologic time scaling. Precam brian now has a detailed proposal for chronostratigraphic subdivision instead of an outdated and ...
7: Geologic Time
This is the difficulty in trying to understand the vastness of geological time—which is measured by millions and billions of years. Essayist John McPhee coined the phrase "deep time" in his 1981 book, Basin and Range. Deep time is truly staggering, a view captured eloquently in a recent essay in the New York Times by Peter Brannen.
11.6: Geologic Time Scale
The geologic time scale is often shown with illustrations of how life on Earth has changed. It sometimes includes major events on Earth, too, such as the formation of the major mountains or the extinction of the dinosaurs. Figure 12.2 shows you a different way of looking at the geologic time scale. It shows how Earth's environment and life ...
Geologic Time Scale
The geologic time scale (GTS) is the principal tool for deciphering and understanding the long and complex history of our planet, Earth. As Arthur Holmes, the father of the geologic time scale, once wrote (Holmes, 1965, p. 148): "To place all the scattered pages of earth history in their proper chronological order is by no means an easy task."." Ordering these scattered and torn pages ...
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gsa geologic time scale v. 5.0 cenozoic age epoch age picks magnetic polarity period hist. chro n. quater-nary pleistocene* miocene oligocene eocene paleocene pliocene piacenzian zanclean messinian tortonian serravallian langhian burdigalian aquitanian chattian rupelian priabonian bartonian lutetian ypresian danian thanetian selandian calabrian ...
3 Geologic Time: From an Early Geologic Time Scale
The geologic time scale was at first built on these principles. However, matching fossil succession and change in organisms to chronostratigraphic events is not an easy task. The original environments where the organisms lived differ from place to place, containing completely different species. Fossilization is a relatively rare process and ...
Geological Time Scale of Earth
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.
Geologic Time Scale: A List of Eons, Eras, and Periods
The geologic time scale is a system used by scientists to describe Earth's history in terms of major geological or paleontological events (such as the formation of a new rock layer or the appearance or demise of certain lifeforms). Geologic time spans are divided into units and subunits, the largest of which are eons. ...
The Eras of the Geologic Time Scale
The Four Eras of the Geologic Time Scale. The Precambrian, Paleozoic, Mesozoic, and Cenozoic Eras. 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.
The Geological Time Scale
This lecture reviews Geologic Time Scale 2004 (Gradstein, Ogg et al., 2004; Cambridge University Press), constructed and detailed by 40 geoscience specialists, and indicates how it will be further refined. Since Geologic Time Scale 1989 by Harland et al., many developments have taken place: (1) Stratigraphic standardization through the work of ...
Geologic Time Scale Estimation
The Geologic Time Scale (GTS) is the framework for deciphering and understanding the long and complex history of our planet, Earth. As Arthur Holmes, the father of the Geologic Time Scale, once wrote (Holmes 1965, p. 148): "To place all the scattered pages of earth history in their proper chronological order is by no means an easy task."." Ordering these pages, and understanding the ...
(PDF) THE GEOLOGICAL TIME SCALE
The geologic time scale is a reference scale for the entire Earth 's history. It helps to understand. the entire history of the earth into workable units. Based on all the available evidences ...
PDF GEOLOGIC TIME SCALE v. 6
geologic time scale v. 6.0 cenozoic mesozoic paleozoic precambrian age epoch age picks magnetic period hist. chro n. polarity quater-nary pleistocene* holocene* calabrian gelasian c1 c2 c2a c3 c3a c4 c4a c5 c5a c6 c6a c6b c6c c7 c5b c5c c5d c5e c8 c9 c10 c7a c11 c12 c13 c15 c16 c17 c18 c19 c20 c21 c22 c23 c24 c25 c26 c27 c28 c29 c30 0.012 1.8 3 ...
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.
Geologic Time Scale Analogy
Geologic Time Scale Analogy Activity Source: Ritger, S.D. and R.H. Cummins. 1991. Using student-created metaphors to comprehend geologic time. ... (see list on the following page). Write an essay that: (1) discusses why you chose the metaphor you used; (2) shows your math calculations; and (3) discusses what you learned from this exercise ...
Free Essay: Geological Time Scale
Procedure. 1. Below you have been provided with a scaled chart to show the geological time scale. Each ___ represents 1 centimeter. The beginning of Earth was 4.6 billion years ago and is represented as 4.6 meters, therefore each centimeter represents 10 million years.
The Geologic Timescale
The Geologic Timescale. The geologic time scale is a system of chronological dating based on the rock record. It classifies geological layers to describe the timing and relationships of events in geologic history. Over hundreds to thousands of millions of years, continents, oceans and mountain ranges have moved both vertically and horizontally.
PDF Re v i e w e r E a r th S c i e n c e
The Geologic Time Scale. The geologic time scale (GTS) is a tool used by geologists in order to classify and date rocks and fossils. Instead of using numerical ages, time is divided into units such as eons, eras, periods, epochs, and ages (in descending order of duration). The GTS is maintained by an international body called the International ...
Deep learning-assisted Bayesian framework for real-time CO 2 leakage
Accurate and efficient localization of CO2 leakage if occurred in subsurface formations, is of significant importance in achieving secure geological carbon sequestration (GCS) projects. However, this task is inherently challenging due to the considerable uncertainties in the subsurface. In this work, we develop a novel deep learning-assisted Bayesian framework for ...

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3 Geologic Time: From an Early 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:

Frequently Asked Questions (FAQs)

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

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

Geologic Time Scale Estimation

Introduction

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Contributions to the Geologic Time Scale

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Earth Science Week Classroom Activities

Instructions

Some Important Dates in the History of the Earth

Geoscientists

Stewardship

Earth Science is all around you

The Geologic Timescale

Discover the history of Geologic time

Stenos Law of Stratigraphy

Index fossils

Find out more about different time periods

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VIDEO

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