is the life on other planets essay

Scientific researchers on a bat-collecting expedition in Sierra Leone. Photo by Simon Townley/Panos

There’s no planet B

The scientific evidence is clear: the only celestial body that can support us is the one we evolved with. here’s why.

by Arwen E Nicholson & Raphaëlle D Haywood   + BIO

At the start of the 22nd century, humanity left Earth for the stars. The enormous ecological and climatic devastation that had characterised the last 100 years had led to a world barren and inhospitable; we had used up Earth entirely. Rapid melting of ice caused the seas to rise, swallowing cities whole. Deforestation ravaged forests around the globe, causing widespread destruction and loss of life. All the while, we continued to burn the fossil fuels we knew to be poisoning us, and thus created a world no longer fit for our survival. And so we set our sights beyond Earth’s horizons to a new world, a place to begin again on a planet as yet untouched. But where are we going? What are our chances of finding the elusive planet B, an Earth-like world ready and waiting to welcome and shelter humanity from the chaos we created on the planet that brought us into being? We built powerful astronomical telescopes to search the skies for planets resembling our own, and very quickly found hundreds of Earth twins orbiting distant stars. Our home was not so unique after all. The universe is full of Earths!

This futuristic dream-like scenario is being sold to us as a real scientific possibility, with billionaires planning to move humanity to Mars in the near future. For decades, children have grown up with the daring movie adventures of intergalactic explorers and the untold habitable worlds they find. Many of the highest-grossing films are set on fictional planets, with paid advisors keeping the science ‘realistic’. At the same time, narratives of humans trying to survive on a post-apocalyptic Earth have also become mainstream.

Given all our technological advances, it’s tempting to believe we are approaching an age of interplanetary colonisation. But can we really leave Earth and all our worries behind? No. All these stories are missing what makes a planet habitable to us . What Earth-like means in astronomy textbooks and what it means to someone considering their survival prospects on a distant world are two vastly different things. We don’t just need a planet roughly the same size and temperature as Earth; we need a planet that spent billions of years evolving with us. We depend completely on the billions of other living organisms that make up Earth’s biosphere. Without them, we cannot survive. Astronomical observations and Earth’s geological record are clear: the only planet that can support us is the one we evolved with. There is no plan B. There is no planet B. Our future is here, and it doesn’t have to mean we’re doomed.

D eep down, we know this from instinct: we are happiest when immersed in our natural environment. There are countless examples of the healing power of spending time in nature . Numerous articles speak of the benefits of ‘forest bathing’; spending time in the woods has been scientifically shown to reduce stress, anxiety and depression, and to improve sleep quality, thus nurturing both our physical and mental health. Our bodies instinctively know what we need: the thriving and unique biosphere that we have co-evolved with, that exists only here, on our home planet.

There is no planet B. These days, everyone is throwing around this catchy slogan. Most of us have seen it inscribed on an activist’s homemade placard, or heard it from a world leader. In 2014, the United Nations’ then secretary general Ban Ki-moon said: ‘There is no plan B because we do not have [a] planet B.’ The French president Emmanuel Macron echoed him in 2018 in his historical address to US Congress. There’s even a book named after it. The slogan gives strong impetus to address our planetary crisis. However, no one actually explains why there isn’t another planet we could live on, even though the evidence from Earth sciences and astronomy is clear. Gathering this observation-based information is essential to counter an increasingly popular but flawed narrative that the only way to ensure our survival is to colonise other planets.

The best-case scenario for terraforming Mars leaves us with an atmosphere we are incapable of breathing

The most common target of such speculative dreaming is our neighbour Mars. It is about half the size of Earth and receives about 40 per cent of the heat that we get from the Sun. From an astronomer’s perspective, Mars is Earth’s identical twin. And Mars has been in the news a lot lately, promoted as a possible outpost for humanity in the near future . While human-led missions to Mars seem likely in the coming decades, what are our prospects of long-term habitation on Mars? Present-day Mars is a cold, dry world with a very thin atmosphere and global dust storms that can last for weeks on end. Its average surface pressure is less than 1 per cent of Earth’s. Surviving without a pressure suit in such an environment is impossible. The dusty air mostly consists of carbon dioxide (CO 2 ) and the surface temperature ranges from a balmy 30ºC (86ºF) in the summer, down to -140ºC (-220ºF) in the winter; these extreme temperature changes are due to the thin atmosphere on Mars.

Despite these clear challenges, proposals for terraforming Mars into a world suitable for long-term human habitation abound. Mars is further from the Sun than Earth, so it would require significantly more greenhouse gases to achieve a temperature similar to Earth’s. Thickening the atmosphere by releasing CO 2 in the Martian surface is the most popular ‘solution’ to the thin atmosphere on Mars. However, every suggested method of releasing the carbon stored in Mars requires technology and resources far beyond what we are currently capable of. What’s more, a recent NASA study determined that there isn’t even enough CO 2 on Mars to warm it sufficiently.

Even if we could find enough CO 2 , we would still be left with an atmosphere we couldn’t breathe. Earth’s atmosphere contains only 0.04 per cent CO 2 , and we cannot tolerate an atmosphere high in CO 2 . For an atmosphere with Earth’s atmospheric pressure, CO 2 levels as high as 1 per cent can cause drowsiness in humans, and once we reach levels of 10 per cent CO 2 , we will suffocate even if there is abundant oxygen. The proposed absolute best-case scenario for terraforming Mars leaves us with an atmosphere we are incapable of breathing; and achieving it is well beyond our current technological and economic capabilities.

Instead of changing the atmosphere of Mars, a more realistic scenario might be to build habitat domes on its surface with internal conditions suitable for our survival. However, there would be a large pressure difference between the inside of the habitat and the outside atmosphere. Any breach in the habitat would rapidly lead to depressurisation as the breathable air escapes into the thin Martian atmosphere. Any humans living on Mars would have to be on constant high alert for any damage to their building structures, and suffocation would be a daily threat.

F rom an astronomical perspective, Mars is Earth’s twin; and yet, it would take vast resources, time and effort to transform it into a world that wouldn’t be capable of providing even the bare minimum of what we have on Earth. Suggesting that another planet could become an escape from our problems on Earth suddenly seems absurd. But are we being pessimistic? Do we just need to look further afield?

Next time you are out on a clear night, look up at the stars and choose one – you are more likely than not to pick one that hosts planets. Astronomical observations today confirm our age-old suspicion that all stars have their own planetary systems. As astronomers, we call these exoplanets. What are exoplanets like? Could we make any of them our home?

The majority of exoplanets discovered to date were found by NASA’s Kepler mission, which monitored the brightness of 100,000 stars over four years, looking for dips in a star’s light as a planet obscures it each time it completes an orbit around it.

Kepler observed more than 900 Earth-sized planets with a radius up to 1.25 times that of our world. These planets could be rocky (for the majority of them, we haven’t yet determined their mass, so we can only make this inference based on empirical relations between planetary mass and radius). Of these 900 or so Earth-sized planets, 23 are in the habitable zone. The habitable zone is the range of orbits around a star where a planet can be considered temperate : the planet’s surface can support liquid water (provided there is sufficient atmospheric pressure), a key ingredient of life as we know it. The concept of the habitable zone is very useful because it depends on just two astrophysical parameters that are relatively easy to measure: the distance of the planet to its parent star, and the star’s temperature. It’s worth keeping in mind that the astronomical habitable zone is a very simple concept and, in reality, there are many more factors at play in the emergence of life; for example, this concept does not consider plate tectonics , which are thought to be crucial to sustain life on Earth.

Planets with similar observable properties to Earth are very common: at least one in 10 stars hosts them

How many Earth-sized, temperate planets are there in our galaxy? Since we have discovered only a handful of these planets so far, it is still quite difficult to estimate their number. Current estimates of the frequency of Earth-sized planets rely on extrapolating measured occurrence rates of planets that are slightly bigger and closer to their parent star, as those are easier to detect. The studies are primarily based on observations from the Kepler mission, which surveyed more than 100,000 stars in a systematic fashion. These stars are all located in a tiny portion of the entire sky; so, occurrence rate studies assume that this part of the sky is representative of the full galaxy. These are all reasonable assumptions for the back-of-the-envelope estimate that we are about to make.

Several different teams carried out their own analyses and, on average, they found that roughly one in three stars (30 per cent) hosts an Earth-sized, temperate planet. The most pessimistic studies found a rate of 9 per cent, which is about one in 10 stars, and the studies with the most optimistic results found that virtually all stars host at least one Earth-sized, temperate planet, and potentially even several of them.

At first sight, this looks like a huge range in values; but it’s worth taking a step back and realising that we had absolutely no constraints whatsoever on this number just 20 years ago. Whether there are other planets similar to Earth is a question that we’ve been asking for millennia, and this is the very first time that we are able to answer it based on actual observations. Before the Kepler mission, we had no idea whether we would find Earth-sized, temperate planets around one in 10, or one in a million stars. Now we know that planets with similar observable properties to Earth are very common: at least one in 10 stars hosts these kinds of planets.

Let’s now use these numbers to predict the number of Earth-sized, temperate planets in our entire galaxy. For this, let’s take the average estimate of 30 per cent, or roughly one in three stars. Our galaxy hosts approximately 300 billion stars, which adds up to 90 billion roughly Earth-sized, roughly temperate planets. This is a huge number, and it can be very tempting to think that at least one of these is bound to look exactly like Earth.

One issue to consider is that other worlds are at unimaginable distances from us. Our neighbour Mars is on average 225 million kilometres (about 140 million miles) away. Imagine a team of astronauts travelling in a vehicle similar to NASA’s robotic New Horizons probe, one of humankind’s fastest spacecrafts – which flew by Pluto in 2015. With New Horizons’ top speed of around 58,000 kph, it would take at least 162 days to reach Mars. Beyond our solar system, the closest star to us is Proxima Centauri, at a distance of 40 trillion kilometres. Going in the same space vehicle, it would take our astronaut crew 79,000 years to reach planets that might exist around our nearest stellar neighbour.

S till, let’s for a moment optimistically imagine that we find a perfect Earth twin: a planet that really is exactly like Earth. Let’s imagine that some futuristic form of technology exists, ready to whisk us away to this new paradise. Keen to explore our new home, we eagerly board our rocket, but on landing we soon feel uneasy. Where is the land? Why is the ocean green and not blue? Why is the sky orange and thick with haze? Why are our instruments detecting no oxygen in the atmosphere? Was this not supposed to be a perfect twin of Earth?

As it turns out, we have landed on a perfect twin of the Archean Earth, the aeon during which life first emerged on our home world. This new planet is certainly habitable: lifeforms are floating around the green, iron-rich oceans, breathing out methane that is giving the sky that unsettling hazy, orange colour. This planet sure is habitable – just not to us . It has a thriving biosphere with plenty of life, but not life like ours. In fact, we would have been unable to survive on Earth for around 90 per cent of its history; the oxygen-rich atmosphere that we depend on is a recent feature of our planet.

The earliest part of our planet’s history, known as the Hadean aeon, begins with the formation of the Earth. Named after the Greek underworld due to our planet’s fiery beginnings, the early Hadean would have been a terrible place with molten lava oceans and an atmosphere of vaporised rock. Next came the Archean aeon, beginning 4 billion years ago, when the first life on Earth flourished. But, as we just saw, the Archean would be no home for a human. The world where our earliest ancestors thrived would kill us in an instant. After the Archean came the Proterozoic, 2.5 billion years ago. In this aeon, there was land, and a more familiar blue ocean and sky. What’s more, oxygen finally began to accumulate in the atmosphere. But let’s not get too excited: the level of oxygen was less than 10 per cent of what we have today. The air would still have been impossible for us to breathe. This time also experienced global glaciation events known as snowball Earths, where ice covered the globe from poles to equator for millions of years at a time. Earth has spent more of its time fully frozen than the length of time that we humans have existed.

We would have been incapable of living on our planet for most of its existence

Earth’s current aeon, the Phanerozoic, began only around 541 million years ago with the Cambrian explosion – a period of time when life rapidly diversified. A plethora of life including the first land plants, dinosaurs and the first flowering plants all appeared during this aeon. It is only within this aeon that our atmosphere became one that we can actually breathe. This aeon has also been characterised by multiple mass extinction events that wiped out as much as 90 per cent of all species over short periods of time. The factors that brought on such devastation are thought to be a combination of large asteroid impacts, and volcanic, chemical and climate changes occurring on Earth at the time. From the point of view of our planet, the changes leading to these mass extinctions are relatively minor. However, for lifeforms at the time, such changes shattered their world and very often led to their complete extinction.

Looking at Earth’s long history, we find that we would have been incapable of living on our planet for most of its existence. Anatomically modern humans emerged less than 400,000 years ago; we have been around for less than 0.01 per cent of the Earth’s story. The only reason we find Earth habitable now is because of the vast and diverse biosphere that has for hundreds of millions of years evolved with and shaped our planet into the home we know today. Our continued survival depends on the continuation of Earth’s present state without any nasty bumps along the way. We are complex lifeforms with complex needs. We are entirely dependent on other organisms for all our food and the very air we breathe. The collapse of Earth’s ecosystems is the collapse of our life-support systems. Replicating everything Earth offers us on another planet, on timescales of a few human lifespans, is simply impossible.

Some argue that we need to colonise other planets to ensure the future of the human race. In 5 billion years, our Sun, a middle-aged star, will become a red giant, expanding in size and possibly engulfing Earth. In 1 billion years, the gradual warming of our Sun is predicted to cause Earth’s oceans to boil away. While this certainly sounds worrying, 1 billion years is a long, long time. A billion years ago, Earth’s landmasses formed the supercontinent Rodinia, and life on Earth consisted in single-celled and small multicellular organisms. No plants or animals yet existed. The oldest Homo sapiens remains date from 315,000 years ago, and until 12,000 years ago all humans lived as hunter-gatherers.

The industrial revolution happened less than 500 years ago. Since then, human activity in burning fossil fuels has been rapidly changing the climate, threatening human lives and damaging ecosystems across the globe. Without rapid action, human-caused climate change is predicted to have devastating global consequences within the next 50 years. This is the looming crisis that humanity must focus on. If we can’t learn to work within the planetary system that we evolved with, how do we ever hope to replicate these deep processes on another planet? Considering how different human civilisations are today from even 5,000 years ago, worrying about a problem that humans may have to tackle in a billion years is simply absurd. It would be far simpler to go back in time and ask the ancient Egyptians to invent the internet there and then. It’s also worth considering that many of the attitudes towards space colonisation are worryingly close to the same exploitative attitudes that have led us to the climate crisis we now face.

Earth is the home we know and love not because it is Earth-sized and temperate. No, we call this planet our home thanks to its billion-year-old relationship with life. Just as people are shaped not only by their genetics, but by their culture and relationships with others, planets are shaped by the living organisms that emerge and thrive on them. Over time, Earth has been dramatically transformed by life into a world where we, humans, can prosper. The relationship works both ways: while life shapes its planet, the planet shapes its life. Present-day Earth is our life-support system, and we cannot live without it.

While Earth is currently our only example of a living planet, it is now within our technological reach to potentially find signs of life on other worlds. In the coming decades, we will likely answer the age-old question: are we alone in the Universe? Finding evidence for alien life promises to shake the foundations of our understanding of our own place in the cosmos. But finding alien life does not mean finding another planet that we can move to. Just as life on Earth has evolved with our planet over billions of years, forming a deep, unique relationship that makes the world we see today, any alien life on a distant planet will have a similarly deep and unique bond with its own planet. We can’t expect to be able to crash the party and find a warm welcome.

Living on a warming Earth presents many challenges. But these pale in comparison with the challenges of converting Mars, or any other planet, into a viable alternative. Scientists study Mars and other planets to better understand how Earth and life formed and evolved, and how they shape each other. We look to worlds beyond our horizons to better understand ourselves. In searching the Universe, we are not looking for an escape to our problems: Earth is our unique and only home in the cosmos. There is no planet B.

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Does life exist outside of the solar system?

Since humans first looked to the cosmos, we have wondered if life exists elsewhere in the Universe. Scientists and engineers at the Center for Astrophysics | Harvard & Smithsonian may soon be able to answer that question.

Scientists and engineers from the Center for Astrophysics aim to achieve the following advances to enable the discovery of life on other planets:

• Understand the Origins of Life: We investigate the conditions of planetary development that made life’s emergence on Earth possible.
• Modeling and Instrumentation: We develop new models for the spectroscopic signatures that identify the composition of planetary atmospheres, and build new instruments to detect them.
• Search and Observation: We identify targeted exoplanet candidates for observation, and continually refine the search process.
• Data Analysis: We use observational data to infer planetary mass, orbit, size, and composition.

How We Search

Exoplanets , or planets in solar systems other than our own, sometimes orbit directly between the Earth and their host star. When the planet orbits in front of its star, it blocks a small amount of light. CfA scientists use the Transiting Exoplanet Survey Satellite (TESS) and the Kepler space telescopes as well as the ground-based robotic telescopes of the MEarth project to look for dips in starlight. This “transit” method of planet hunting has revealed thousands of exoplanets.

During a transit, a small amount of starlight is absorbed by the planet’s atmosphere, yielding clues to the chemical makeup of the atmosphere. A massive, technologically advanced telescope is crucial for detecting the composition of an Earth-like planet’s atmosphere, including the subtle chemical signatures that life is expected to produce.

Thanks to next generation telescopes like the planned Giant Magellan Telescope (GMT) , we are approaching a point in our observational capabilities that may allow us to make previously unthinkable discoveries. One of these breakthroughs is the detection of life on a distant planet, light years away from Earth.

Juliana Garcia-Mejia working on the GMT-Consortium Large Earth Finder (G-CLEF) spectrograph for the Giant Magellan Telescope, in a lab at CfA in Cambridge, MA.

Theory of Life

Institute for Theory and Computation scientists at the CfA work on identifying the exoplanets that are most likely to harbor life. The orbit must lie in the “habitable zone” where the exoplanet’s surface is just the right temperature for liquid water to exist. Every form of life we know requires liquid water, so an exoplanet too close or too far from its host star is less likely to contain life. Additionally, ultraviolet light may be needed to form some necessary prebiotic molecules, but an overactive host star can blast the young planet, stripping away its atmosphere. When searching for extraterrestrial life, finding the perfect star could be as important as finding the perfect exoplanet.

Our Next Tool

The G-CLEF or GMT-Consortium Large Earth Finder, a next-generation spectrometer planned for use on the GMT, is our newest tool for measuring the starlight filtered through the atmosphere of an orbiting exoplanet. Using this instrument, scientists will soon be able to measure the chemical composition of a small rocky exoplanet’s atmosphere. Such an extraordinary feat is like trying to see through and study the antennae of a moth flying in front of a spotlight.

Based on our current understanding of the conditions necessary for life, the detection of biomarkers like oxygen in the atmosphere of a remote world through such observations would hint towards the presence of living organisms.

• Astro Combs
• Planetary Atmospheres
• Life in the Universe
• The Milky Way Galaxy
• Extragalactic Astronomy
• Theoretical Astrophysics
• Planetary Systems
• Stellar Astronomy
• Radio and Geoastronomy
• Solar, Stellar, and Planetary Sciences

When we look at our own planet Earth, we see life that abounds everywhere. Do these same conditions exist elsewhere in the Universe? Remarkably, 21st Century science and engineering may soon answer that question. Dr. Charles Alcock, Director, The Center for Astrophysics

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The Great Galaxy M–31 in the constellation Andromeda. This is the nearest galaxy to our own, and resembles it in many ways. The dark rifts are enormous cosmic dust clouds from which stars are thought to form. In each galaxy there may be 100 million planets on which life exists. (University of Chicago Photographic Archive, apf6-02681 , Special Collections Research Center, University of Chicago Library)

From our print archive: In spite of the hours clocked at super-spyglasses, astronomers have yet to spot any little green men on Mars or any other planet. But they have made some pretty convincing observations that life does exist on other planets.

Is there life on other worlds? If other planets can support life chemically as we know it here on earth, how does this relate to the origin of life itself?

Scientists have long speculated on the theory that life in its most primitive form may be the next step in cosmic evolution after the formation of planets. While this is still only a theory, new ideas on planetary origin and recent discoveries in chemistry have given it support.

For example, forty million miles from Earth, at this writing, is Mars, a planet colder than the earth, with no oxygen in its atmosphere, and little water on its surface. A man transported to Mars would gasp and die—and most other familiar organisms would also perish.

Yet, for over half a century astronomers have observed slight seasonal color variations on the planet; variations apparently coinciding with the availability of water. These have been interpreted as evidence for plant life on Mars, life specifically adapted to the rigors of the Martian environment. If the reported color changes are real, there seems to be no other reasonable interpretation.

Further, marginal spectroscopic observations by W. M. Sinton suggest that there may be molecules with C-H bonds on the surface of Mars. Carbon and hydrogen are fundamental elements for all terrestrial organisms, and the chemical bond combining them is essential for the structure of proteins, nucleic acids, and other biological building blocks. Is it possible, then, that the same sort of life, similar in its basic chemical makeup, has originated twice in the same solar system? While speculative in some of its details, the general pattern of cosmic evolution is fairly well established.

Cosmic evolution begins with an enormous cosmic dust cloud, such as exists today between the stars. Such a cloud has a “cosmic” abundance of the elements, being composed primarily of hydrogen and helium, with only a small admixture of heavier elements. Here and there matter will be somewhat more dense than in nearby regions. The more diffuse regions will be gravitationally attracted to the denser region, which, in consequence, will grow in size and mass. As matter streams in towards the condensing central nucleus, conservation of angular momentum will cause the whole region, nucleus and streaming matter, to rotate faster and faster.

In addition, as large amounts of matter continue to collide with the nucleus, its temperature will steadily rise. After perhaps a hundred million years, the temperature at the center of the cloud will have risen to about fifteen million degrees. This is the ignition temperature for thermonuclear reactions, (such as the conversion of hydrogen to helium in the hydrogen bomb). At this time the nucleus of the cloud will become a star, “turning on” and radiating light and heat into nearby space. If the rotation is sufficiently fast, the forming star will separate under certain conditions into smaller parts, producing a double or multiple star system.

Now as the star forms, there still is a large dust cloud surrounding the star and rotating with it. In this cloud, the solar nebula, small, denser regions begin attracting nearby matter, as in star formation. However, the protoplanets that grow from these regions, (in the gravitational field of the nearby star), never rise by collisional heating to the thermonuclear ignition temperature, and so become planets and not stars.

Gerard P. Kuiper, professor of astronomy at Yerkes Observatory, has described how planets are formed in this manner in recent years. In the forming protoplanets, there would be a tendency for the heavier elements to sink to the center, leaving the much more abundant hydrogen and helium as the principal constituents of the atmosphere surrounding the new planets. When the newly formed star “turns on,” radiation pressure will tend to blow away this atmosphere.

However, if the protoplanet is very massive, or very far from the sun, the gravitational attraction of the protoplanet for a gas molecule may be greater than the force of radiation trying to blow it away, and the protoplanet may retain an atmosphere. This atmosphere can be residual from the proto-atmosphere, or may be due to gaseous exhalations from the planetary interior. For example, the earth’s present atmosphere is due to exhalations; Jupiter’s present atmosphere is residual.

In such a way, one can understand, generally, the atmospheres of the planets in this solar system:

• Mercury : Not massive, close to the sun, retains negligible atmosphere.
• Venus : More massive than Mercury, further from the sun, retains only the heavy gas, carbon dioxide.
• Earth : Retain s the lighter gases, nitrogen, oxygen, and water vapor, but has lost almost all hydrogen and helium.
• Mars : Although further from the sun, is less massive than Earth or Venus, and so retains principally only the heavy gas, carbon dioxide.
• Jupiter, Saturn, Uranus, Neptune : Much further from the sun and very massive, they retain much hydrogen and helium, while the other planets have lost theirs.

One fact about our solar system that has rung the death knell of many cosmogonies is the fact that although over 99 per cent of the mass of the solar system is in the sun, over 98 per cent of the angular momentum of the system is in the planets. It is as if the rotational inertia has been transferred from the sun to the planets. H. Alfven has explained this as a magnetic braking of the sun’s rotation, due to the interaction of “its magnetic field with the ionized solar nebula. On this basis, the existence of a solar nebula from which planetary systems form will cause the central star to rotate more and more slowly.

Now the origin of planets must be dependent on the temperature of the central star. If it is too cold, the atmosphere of the protoplanets will not be blown away, resulting perhaps in the formation of a system of planets similar to Jupiter, but even larger and more massive. On the other hand, if the star is too hot, radiation pressure will disperse the solar nebula rapidly, leaving, if anything, small atmosphereless planets, or a system of millions of tiny asteroids. For planets to be formed, the temperature of the star must be between these extremes.

There is another reason to believe that hot stars do not have planets. If the formation of planetary systems and the slowing down of stellar rotation both arise from the existence of solar nebulae, then we should expect the hot stars which dissipate their solar nebulae and do not form planets to rotate faster. This is exactly what is observed! The hotter the star, the faster the rotation. Cooler stars rotate more slowly than would otherwise be expected.

At a temperature of about 7,000 degrees, characteristic of what are called F stars, there is a sudden large decrease in average rotational velocities, and it is possible, perhaps, that below this temperature all stars retain enough of their solar nebulae to form planets, (provided they have not used up their solar nebulae in forming double or multiple sun systems).

The number of such stars is between one and ten per cent of the total number of stars, suggesting that there are as many as ten billion solar systems in our galaxy alone. Of these, perhaps one per cent, or 100 million have planets like the earth. What is the probability of life on these worlds?

Since the most abundant element, cosmically, is hydrogen, the atmosphere of the early protoplanets of any system must contain much hydrogen and hydrogen compounds. The hydrogen compounds of carbon, nitrogen, and oxygen are probably the most abundant hydrogen compounds in the proto-atmosphere. They are, respectively, methane, CH4, ammonia, NH3, and water vapor, H20.

In 1953, Stanley Miller, PhD’54, then a graduate student working under professor Harold C. Urey showed that when hydrogen, methane, ammonia, and water vapor are mixed together, and supplied with energy, some fundamental organic compounds are produced. (The energy source in protoatmospheres is probably ultraviolet light from the sun about which the protoplanet revolves.)

These compounds are almost all amino acids, the biochemical building blocks from which protein is constructed. There is also some reason to believe that amino acids lead to the formation of purines and pyrimidines, which are in turn building blocks for nucleic acids. Proteins and nucleic acids are the two fundamental constituents of life as we know it on earth; hereditary materials such as genes and chromosomes are composed perhaps exclusively of nucleic acids and proteins. In addition, enzymes, which catalyze slow chemical reactions and thereby make complex life forms possible, are always proteins.

Experiments of comparable importance to those of Miller have been performed by S. W. Fox. Fox applied heat, in the range between 100 and 200 degrees Centigrade, to simple molecules, such as those synthesized by Miller. This simple procedure produced small amounts of complex organic molecules that happen to be widely distributed in all terrestrial organisms. In particular, Fox has produced ureidosuccinic acid, a key intermediary in the synthesis of nucleic acids. The temperatures required by Fox can easily be supplied by radioactive heating of the crust of the planet. There is evidence that such radioactive heating is a normal part of the early evolution of all planets.

Now it is really striking that the molecules produced by Miller and Fox are precisely the molecules necessary to form life as we know it. Almost no molecules were produced which are not fundamentally involved in modern terrestrial organisms.

The processes described by Miller and Fox would probably occur on at least one planet of each star of moderate temperature. All that is required is a way of collecting the molecules produced by these processes into one place where they can interact. A liquid medium on the surface of the planet serves this purpose admirably. Molecules produced in the atmosphere would fall into these bodies of liquid, and molecules produced on land by the application of heat would also be washed into them. Although seas of liquid ammonia or hydrofluoric acid would serve, it can be shown that seas of water would be most efficient in collecting and preserving the bio-molecules.

The one planet in each system that we are considering probably possessed liquid water seas early in its history, and therefore on such planets the production of proteins and nucleic acids may be expected.

Now proteins and nucleic acids have some unusual properties; so far as we know, ones not found in any other molecules. They can form a new molecule which not only can construct other identical molecules from the matter floating in the sea around it, but which if changed in some way can also construct copies of its changed structure. Such a mutating, self-reproducing molecule or collection of molecules must undergo natural selection. For these reasons, it must be identified as the first living being on the planet in question.

Thus, there may be 100 million planets in this galaxy alone on which flourish organisms at least biochemically akin to ourselves. On the other hand, due to natural selection, these organisms must be well adapted, each to its own environment. Since even slight differences in the environment eventually cause extreme differences in the structure of organisms, we should not accept extraterrestrial lifeforms to resemble anything familiar. But there is reason to believe they are out there.

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Many scientists believe we are not alone in the universe. It’s probable, they say, that life could have arisen on at least some of the billions of planets thought to exist in our galaxy alone — just as it did here on planet Earth. This basic question about our place in the Universe is one that may be answered by scientific investigations. What are the next steps to finding life elsewhere?

Experts from NASA and its partner institutions addressed this question on July 14, at a public talk held at NASA Headquarters in Washington. They outlined NASA’s roadmap to the search for life in the universe, an ongoing journey that involves a number of current and future telescopes. Watch the video of the event:

“Sometime in the near future, people will be able to point to a star and say, ‘that star has a planet like Earth’,” says Sara Seager, professor of planetary science and physics at the Massachusetts Institute of Technology in Cambridge, Massachusetts. “Astronomers think it is very likely that every single star in our Milky Way galaxy has at least one planet.”

NASA’s quest to study planetary systems around other stars started with ground-based observatories, then moved to space-based assets like the Hubble Space Telescope , the Spitzer Space Telescope , and the Kepler Space Telescope . Today’s telescopes can look at many stars and tell if they have one or more orbiting planets. Even more, they can determine if the planets are the right distance away from the star to have liquid water, the key ingredient to life as we know it.

The NASA roadmap will continue with the launch of the Transiting Exoplanet Surveying Satellite (TESS) in 2017, the James Webb Space Telescope (Webb Telescope) in 2018, and perhaps the proposed Wide Field Infrared Survey Telescope – Astrophysics Focused Telescope Assets (WFIRST-AFTA) early in the next decade. These upcoming telescopes will find and characterize a host of new exoplanets — those planets that orbit other stars — expanding our knowledge of their atmospheres and diversity. The Webb telescope and WFIRST-AFTA will lay the groundwork, and future missions will extend the search for oceans in the form of atmospheric water vapor and for life as in carbon dioxide and other atmospheric chemicals, on nearby planets that are similar to Earth in size and mass, a key step in the search for life.

“This technology we are using to explore exoplanets is real,” said John Grunsfeld, astronaut and associate administrator for NASA’s Science Mission Directorate in Washington. “The James Webb Space Telescope and the next advances are happening now. These are not dreams — this is what we do at NASA.”

Since its launch in 2009, Kepler has dramatically changed what we know about exoplanets, finding most of the more than 5,000 potential exoplanets, of which more than 1700 have been confirmed. The Kepler observations have led to estimates of billions of planets in our galaxy, and shown that most planets within one astronomical unit are less than three times the diameter of Earth. Kepler also found the first Earth-size planet to orbit in the “habitable zone” of a star, the region where liquid water can pool on the surface.

“What we didn’t know five years ago is that perhaps 10 to 20 percent of stars around us have Earth-size planets in the habitable zone,” says Matt Mountain, director and Webb telescope scientist at the Space Telescope Science Institute in Baltimore. “It’s within our grasp to pull off a discovery that will change the world forever. It is going to take a continuing partnership between NASA, science, technology, the U.S. and international space endeavors, as exemplified by the James Webb Space Telescope, to build the next bridge to humanity’s future.”

This decade has seen the discovery of more and more super Earths, which are rocky planets that are larger and heftier than Earth. Finding smaller planets, the Earth twins, is a tougher challenge because they produce fainter signals. Technology to detect and image these Earth-like planets is being developed now for use with the future space telescopes. The ability to detect alien life may still be years or more away, but the quest is underway.

Said Mountain, “Just imagine the moment, when we find potential signatures of life. Imagine the moment when the world wakes up and the human race realizes that its long loneliness in time and space may be over — the possibility we’re no longer alone in the universe.”

Life on Other Planets Essay Example

A major discussion and debate has arisen among scientists and the general public about life on other planets, and whether or not it is possible. While it is possible for there to be life on other planets, a bigger question is brought up: whether or not the other planets can develop and sustain complex life, equivalent to that of Earth. While many do think the universe is too large for there not to be a human race equivalent, it is rebuked by facts and probability about the multitude of conditions needed for comparable advanced life to thrive and even simpler the conditions for the planet itself to be comparable to Earth. An analysis of the facts given in the article, “The Two Billion Earthlike Planets in the Milky Way” by Casey Kazan proves moreover that it is nearly impossible for equivalent life to exist. 

There is the argument made by many that the number of planets in the universe is so great that at least one other planet should be able to sustain life. Even though not found quite yet, there is much speculation around life being found relatively soon on other planets in our solar system. For example, “... life on the microbial level will be discovered sometime in the next twenty years on Mars or on one of Jupiter or Saturn’s moons” (Kazan, 2). Also, there is an attempt to back up this possibility with the fact that these planets have similar components to Earth, such as mass, size, and even the chemical elements that are present; these are all pivotal in establishing an environment crucial to forming and sustaining any form of life. Due to these components, many have come to believe that the possibility of life could be possible and it just has not been discovered yet. 

However, all of these supporting claims can be rebutted by the main fact that to be similar to Earth all of the factors need to align. For example, “Size alone, for example, doesn’t say enough about habitability” (Kazan, 1), this proves that there needs to be a variety, if not all, of the same components to create a similar planet capable of sustaining life as it is known on Earth. All components of the planet must be similar if not the same, as well as aspects such as the stars of this planet, the surrounding planets, and a moon that stabilizes the planet's tilt, to name a few. Lastly, major events that laid the pathway for Earth's evolution need to align such as giant impacts, and even more simply, biological evolution. Additionally, with all of these factors taken into consideration, it was found that “... the zones and regions of the known universe described below are the ones that astrobiologists have concluded have little or zero chance of supporting life as we know it” (Kazan, 2). While the possibility of short-term life on other planets is possible it can not be compared to that of life on Earth and its processes of evolution. After a deep analysis and understanding, it is clearly accepted that the statistics given in the document about the probability of a planet having the same evolutionary processes from the planet itself to the organisms created is nearly impossible.

Overall, the possibility of life existing on other planets similar to Earth is widely debated, but data inevitably the data shows that it is nonviable for this comparable planet to exist. Also, the theory’s behind the possibility of this planet are just abstract possibilities based on just that, possibilities but not factual data. The last thing to think about in this debate is whether or not we humans can aid in the creation and sustainability of potential life on these Earth-like planets in the years to come. Until there is the exploration of this comparable planet found somewhere in the galaxy it is widely accepted that Earth is the only of its kind able to support complex life.

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Life on Other Planets Essay

Article review.

The article chosen for this part of the assignment is titled “The Extremely Halophilic Microorganisms, a Possible Model for Life on Other Planets,” written by Sergiu Fendrihan, and published in 2017 in Current Trends in Natural Sciences journal. The researchers have analyzed the microscopic life that exists in areas of extreme heat, where water supply exists in the form of salt lakes (Fendrihan 148). Such areas include the Dead Sea, located in the Middle East, as well as various smaller salt lakes found in Africa and Australia.

What these locations have in common is the extremity of conditions in which microorganisms have to exist. According to Fendrihan (148), there is a multitude of halophilic and halotolerant microorganisms inhabiting these areas, up to 159 different subspecies belonging to the Halobacteriaceae family. In addition, these organisms prove to be very resistant to other extremes, such as UV radiation, heat, and lack of nutrients necessary for other bacteria.

Due to the extreme resistance of these bacteria to various hazards, this study provides important data for discovering life on other planets and moons. Mars exhibits signs of water having been present on its surface. In addition, evidence of salty underground oceans has been found on the moons of Saturn and Jupiter (Enceladus and Europa).

Thus, studying halophilic microorganisms supports the possibility of the existence of life on planets previously deemed uninhabitable. Low requirements for water and nutrients as well as high resistance to the elements increases their chances of survival. Investigating these planets would enrich the existing knowledge of space and biology.

Article Discussions

The article titled “Life on Mars: Exploration and Evidence” by Nola Taylor Redd provides cursory information about the state of research regarding life on Mars. The planet used to have large water deposits that were lost due to irradiation and exposure to harsh temperatures. The article suggests that life on Mars may still exist underneath the surface of the planet (Redd). Question: What exactly happened that altered Mars’s climate and caused it to lose so much of its water?

The second article titled “Aliens May Well Exist in a Parallel Universe, New Studies Find” by Brandon Specktor speculates about the existence of life in other dimensions. This article seems more like speculation rather than a contribution to the scientific community, as evidence of the existence of other dimensions is purely theoretical (Specktor). Question: If parallel universes exist, can they influence the events in our universe?

The third article titled “The Four Best Places for Life in Our Solar System” by Nicole Mortillaro provides a summary of four potential places for finding life. These planets and moons include Mars, Europa, Enceladus, and Titan (Mortillaro). This article outlines the requirements currently used to determine the feasibility of life on other planets. Question: Why did NASA restrict itself to studying Mars instead of sending a drone on one of the moons?

The fourth article written by Mike Wall speaks of the protective gravitational barrier of our solar system, which filters out charged particles coming from outside of the solar system. The existence of this protective field makes life on Earth possible (Wall). Studying it would help determine which systems can potentially harbor life and which could not. Question: Is the gravitational barrier unique to the Solar system alone?

The fifth article written by Lisa Kaspin-Powell explores the potential of non-H2O-based lifeforms existing on Titan. The article informs the readers that the elements found in Titan’s atmosphere can form cellular membranes similar to phospholipid molecular chains (Kaspin-Powell). Question: What other elements could potentially form cellular membranes?

The last article written by Seth Shostack provides a list of eight planets within the scope of our solar system that has the potential of harboring life. Aside from the 4 candidates mentioned in the article by Mortillaro, the article adds Earth, Venus, Ganymede, and Callisto, which show gravitational signs of possessing underground water (Shostak). Question: How is gravity related to the presence or absence of water?

Works Cited

Fendrihan, Sergiu. “The Extremely Halophilic Microorganisms, A Possible Model for Life on Other Planets.” Current Trends in Natural Sciences, vol. 6, no. 12, 2017, pp. 147-151.

Kaspin-Powell, Lisa. “Does Titan’s Hydrocarbon Soup Hold a Recipe for Life?” Astrobiology Magazine . 2018. Web.

Mortillaro, Nicole. “ The Four Best Places for Life in Our Solar System .” Global News . 2014. Web.

Redd, Nola Taylor. “ Life on Mars: Exploration and Evidence. ” Space. 2017. Web.

Shostak, Seth. “ 8 Worlds Where Life Might Exist. ” Space. 2006. Web.

Specktor, Brandon. “ Aliens May Well Exist in a Parallel Universe, New Studies Find. ” Space. 2018. Web.

Wall, Mike. “ NASA Will Launch a Probe to Study the Solar System’s Protective Bubble in 2024. ” Space. 2018. Web.

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IvyPanda. (2023, December 13). Life on Other Planets. https://ivypanda.com/essays/life-on-other-planets/

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IvyPanda . 2023. "Life on Other Planets." December 13, 2023. https://ivypanda.com/essays/life-on-other-planets/.

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• 16 October 2023

How would we know whether there is life on Earth? This bold experiment found out

• Alexandra Witze

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Anything down there? Earth as seen by the Galileo probe in 1990. Credit: NASA/JPL

It began the way many discoveries do — a tickling of curiosity in the back of someone’s mind. That someone was astronomer and communicator Carl Sagan. The thing doing the tickling was the trajectory of NASA’s Galileo spacecraft, which had launched in October 1989 and was the first to orbit Jupiter. The result was a paper in Nature 30 years ago this week that changed how scientists thought about looking for life on other planets.

The opportunity stemmed from a tragic mishap. Almost four years before Galileo’s launch, in January 1986, the space shuttle Challenger had exploded shortly after lift-off, taking seven lives with it. NASA cancelled its plans to dispatch Galileo on a speedy path to Jupiter using a liquid-fuelled rocket aboard another space shuttle. Instead, the probe was released more gently from an orbiting shuttle, with mission engineers slingshotting it around Venus and Earth so it could gain the gravitational boosts that would catapult it all the way to Jupiter.

On 8 December 1990, Galileo was due to skim past Earth, just 960 kilometres above the surface. The tickling became an itch that Sagan had to scratch. He talked NASA into pointing the spacecraft’s instruments at our planet. The resulting paper was titled ‘A search for life on Earth from the Galileo spacecraft’ 1 .

The outside view

We are in a unique position of knowing that life exists on Earth. To use our own home to test whether we could discern that remotely was an extraordinary suggestion at the time, when so little was known about the environments in which life might thrive. “It’s almost like a science-fiction story wrapped up in a paper,” says David Grinspoon, senior scientist for astrobiology strategy at NASA’s headquarters in Washington DC. “Let’s imagine that we’re seeing Earth for the first time.”

It came at a time, too, when the search for life elsewhere in the Solar System was at a low ebb. US and Soviet robotic missions in the 1960s and 1970s had revealed that Venus — once thought to be a haven for exotic organisms — was hellishly hot beneath its dense clouds of carbon dioxide. Mars, crisscrossed by the ‘irrigation canals’ of astronomers’ imagination 2 , was a seemingly barren wasteland. In 1990, no one yet knew about the buried oceans that lay on Jupiter’s moon Europa — a discovery that Galileo would go on to make 3 — or on Saturn’s moon Enceladus, both of which are now seen as potential cradles of extraterrestrial life.

Crucially, Sagan and his collaborators took a deliberately agnostic approach to the detection of life, says astrobiologist Lisa Kaltenegger, who heads the Carl Sagan Institute at Cornell University in Ithaca, New York. “Of course he wants to find life, every scientist does,” she says. “But he says, let’s take that wish and be even more cautious — because we want to find it.” The existence of life was to be, in the words of the paper, the “hypothesis of last resort” for explaining what Galileo observed.

But even through this veil of scepticism, the spacecraft delivered. High-resolution images of Australia and Antarctica obtained as Galileo flew overhead did not yield signs of civilization. Still, Galileo measured oxygen and methane in Earth’s atmosphere, the latter in ratios that suggested a disequilibrium brought about by living organisms. It spotted a steep cliff in the infrared spectrum of sunlight reflecting off the planet, a distinctive ‘red edge’ that indicates the presence of vegetation. And it picked up radio transmissions coming from the surface that were moderated as if engineered. “A strong case can be made that the signals are generated by an intelligent form of life on Earth,” Sagan’s team wrote, rather cheekily.

A powerful control

Karl Ziemelis, now chief physical sciences editor at Nature , handled the paper as a rookie editor. He says it remains one of his favourites — and one of the hardest to get in. Editorial approval for the paper was far from unanimous, because it was not obviously describing something new. But, according to Ziemelis, that was mostly beside the point. “It was an incredibly powerful control experiment for something that wasn’t really on many people’s radar at the time,” he says.

“While the answer was known, it profoundly changed our way of thinking about the answer,” says Kaltenegger. Only by stepping back and regarding Earth as a planet like any other — perhaps harbouring life, perhaps not — can researchers begin to get a true perspective on our place in the Universe and the likelihood of life elsewhere, she says.

No sign of civilization in Australia. Credit: NASA/JPL

It takes on a new importance given developments since the Galileo flyby. In 1990, no planets orbiting stars other than the Sun were known. It was another two years before astronomers conclusively reported the first ‘exoplanet’ orbiting a rotating dead star known as a pulsar 4 , and three years more before they found 5 the first around a Sun-like star, 51 Pegasi. Today, scientists know of more than 5,500 exoplanets, few of which look like anything in the Solar System. They range from ‘super-Earths’ with bizarre geologies and ‘mini-Neptunes’ with gassy atmospheres to ‘hot Jupiters’, huge planets whirling close to their blazing stars.

When Sagan and his colleagues pointed Galileo at Earth, they invented a scientific framework for looking for signs of life on these other worlds — one that has permeated every search for such biosignatures since. Kaltenegger still gives Sagan’s paper to her students to show them how it is done. Life is the last, not first, inference to draw when seeing something unusual on another planet, she tells them. Extraordinary claims require extraordinary evidence.

The right mix for life

This lesson could not be more important today, as scientists stand on the verge of potentially revolutionary, and perhaps monumentally confusing, discoveries by the powerful James Webb Space Telescope (JWST). The telescope is just beginning its remote exploration of the atmospheres of dozens of exoplanets, hunting for the same sort of chemical disequilibrium that Galileo spotted in Earth’s atmosphere. It is already turning up early hints of biosignatures that might lead scientists and the public astray.

For instance, JWST has sniffed out methane in the atmosphere of at least one planet. That gas is a powerful signature of life on Earth, but it can also come from volcanoes, no life required. Oxygen captures scientists’ attention because much of it is generated by life on Earth, but it can also be formed by light splitting apart molecules of water or carbon dioxide. Finding the right combination of methane and oxygen could indicate the presence of life on another planet — but that world needs to be located in a temperate zone, not too hot nor too cold. Getting the right mix of life-sustaining ingredients in a life-friendly environment is challenging, Kaltenegger says.

The same is true for other intriguing mixes of atmospheric gases. Just last month, astronomers sifting through JWST data reported finding methane and carbon dioxide in the atmosphere of a large exoplanet called K2-18 b. They suggested that the planet might have water oceans covering its surface, and hinted at tantalizing detections of dimethyl sulfide, a compound that, on Earth, comes from phytoplankton and other living organisms 6 .

Headlines ran wild, with news stories reporting possible signs of life on K2-18 b. Never mind that the presence of dimethyl sulfide was reported with low confidence and needed further validation. Nor that no water had actually been detected on the planet. And, even if water were present, it might be in an ocean so deep as to choke off all geological activity that could maintain a temperate atmosphere.

Building evidence

Challenges such as these led Jim Green, a former chief scientist at NASA, to propose a framework in 2021 for how to report evidence for life beyond Earth 7 . A progressive scale, from one to seven, for example, could help to convey the level of evidence for life in a particular discovery, he argues. Maybe you’ve got a signal that could result from biological activity — that would just be a one on the scale. You’d need to work through many more steps, such as ruling out contamination and acquiring independent evidence of the strength of that signal before you could get to level 7 and demonstrate a true discovery of life beyond Earth.

It could take a long time. A telescope might sniff out an intriguing molecule, and scientists would argue about it. Another telescope might be built to work out the context of the observation. Each brick of evidence must be placed on top of another, each layer of mortar mixed through the arguments, scepticism and agnosticism of many, many scientists. And that’s assuming that life on another world resembles that on Earth — an assumption underlying the conclusions drawn from Galileo’s observations. “The uncertainty may last years or decades,” Grinspoon says. Sagan, who died in 1996, would have loved it.

The same year that Galileo observed Earth, Sagan convinced NASA to point another spacecraft in a direction the agency had not been planning. As Voyager 1 raced past Neptune on its way out of the Solar System, it turned its cameras back towards Earth and photographed a tiny speck, gleaming in a sunbeam. This was the iconic Pale Blue Dot image that inspired Sagan to ruminate in his 1994 book Pale Blue Dot : “That’s here. That’s home. That’s us.”

That fragile gleaming pixel reshaped how humanity visualizes its place in the Cosmos. So, too, did using Galileo to look for life on Earth, says Kaltenegger: “This is how we can use our pale blue dot to provide a template for the search for life on other planets.”

Nature 622 , 451-452 (2023)

doi: https://doi.org/10.1038/d41586-023-03230-z

Sagan, C., Thompson, W. R., Carlson, R., Gurnett, D. & Hord, C. Nature 365 , 715–721 (1993).

Article   PubMed   Google Scholar  

Sagan, C. & Pollack, J. B. Nature 212 , 117–121 (1966).

Article   Google Scholar  

Kivelson, M. G. et al. Science 289 , 1340–1343 (2000).

Wolszczan, A. & Frail, D. A. Nature 355 , 145–147 (1992).

Mayor, M. & Queloz, D. Nature 378 , 355–359 (1995).

Madhusudhan, N. et al. Preprint at https://arxiv.org/abs/2309.05566 (2023).

Green, J. et al. Nature 598 , 575–579 (2021).

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The origin of life on Earth, explained

The origin of life on Earth stands as one of the great mysteries of science. Various answers have been proposed, all of which remain unverified. To find out if we are alone in the galaxy, we will need to better understand what geochemical conditions nurtured the first life forms. What water, chemistry and temperature cycles fostered the chemical reactions that allowed life to emerge on our planet? Because life arose in the largely unknown surface conditions of Earth’s early history, answering these and other questions remains a challenge.

Several seminal experiments in this topic have been conducted at the University of Chicago, including the Miller-Urey experiment that suggested how the building blocks of life could form in a primordial soup.

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• When did life on Earth begin?

Where did life on Earth begin?

What are the ingredients of life on earth, what are the major scientific theories for how life emerged, what is chirality and why is it biologically important, what research are uchicago scientists currently conducting on the origins of life, when did life on earth begin .

Earth is about 4.5 billion years old. Scientists think that by 4.3 billion years ago, Earth may have developed conditions suitable to support life. The oldest known fossils, however, are only 3.7 billion years old. During that 600 million-year window, life may have emerged repeatedly, only to be snuffed out by catastrophic collisions with asteroids and comets.

The details of those early events are not well preserved in Earth’s oldest rocks. Some hints come from the oldest zircons, highly durable minerals that formed in magma. Scientists have found traces of a form of carbon—an important element in living organisms— in one such 4.1 billion-year-old zircon . However, it does not provide enough evidence to prove life’s existence at that early date.

Two possibilities are in volcanically active hydrothermal environments on land and at sea.

Some microorganisms thrive in the scalding, highly acidic hot springs environments like those found today in Iceland, Norway and Yellowstone National Park. The same goes for deep-sea hydrothermal vents. These chimney-like vents form where seawater comes into contact with magma on the ocean floor, resulting in streams of superheated plumes. The microorganisms that live near such plumes have led some scientists to suggest them as the birthplaces of Earth’s first life forms.

Organic molecules may also have formed in certain types of clay minerals that could have offered favorable conditions for protection and preservation. This could have happened on Earth during its early history, or on comets and asteroids that later brought them to Earth in collisions. This would suggest that the same process could have seeded life on planets elsewhere in the universe.

The recipe consists of a steady energy source, organic compounds and water.

Sunlight provides the energy source at the surface, which drives photosynthesis. On the ocean floor, geothermal energy supplies the chemical nutrients that organisms need to live.

Also crucial are the elements important to life . For us, these are carbon, hydrogen, oxygen, nitrogen, and phosphorus. But there are several scientific mysteries about how these elements wound up together on Earth. For example, scientists would not expect a planet that formed so close to the sun to naturally incorporate carbon and nitrogen. These elements become solid only under very cold temperatures, such as exist in the outer solar system, not nearer to the sun where Earth is. Also, carbon, like gold, is rare at the Earth’s surface. That’s because carbon chemically bonds more often with iron than rock. Gold also bonds more often with metal, so most of it ends up in the Earth’s core. So, how did the small amounts found at the surface get there? Could a similar process also have unfolded on other planets?

The last ingredient is water. Water now covers about 70% of Earth’s surface, but how much sat on the surface 4 billion years ago? Like carbon and nitrogen, water is much more likely to become a part of solid objects that formed at a greater distance from the sun. To explain its presence on Earth, one theory proposes that a class of meteorites called carbonaceous chondrites formed far enough from the sun to have served as a water-delivery system.

There are several theories for how life came to be on Earth. These include:

Life emerged from a primordial soup

As a University of Chicago graduate student in 1952, Stanley Miller performed a famous experiment with Harold Urey, a Nobel laureate in chemistry. Their results explored the idea that life formed in a primordial soup.

Miller and Urey injected ammonia, methane and water vapor into an enclosed glass container to simulate what were then believed to be the conditions of Earth’s early atmosphere. Then they passed electrical sparks through the container to simulate lightning. Amino acids, the building blocks of proteins, soon formed. Miller and Urey realized that this process could have paved the way for the molecules needed to produce life.

Scientists now believe that Earth’s early atmosphere had a different chemical makeup from Miller and Urey’s recipe. Even so, the experiment gave rise to a new scientific field called prebiotic or abiotic chemistry, the chemistry that preceded the origin of life. This is the opposite of biogenesis, the idea that only a living organism can beget another living organism.

Seeded by comets or meteors

Some scientists think that some of the molecules important to life may be produced outside the Earth. Instead, they suggest that these ingredients came from meteorites or comets.

“A colleague once told me, ‘It’s a lot easier to build a house out of Legos when they’re falling from the sky,’” said Fred Ciesla, a geophysical sciences professor at UChicago. Ciesla and that colleague, Scott Sandford of the NASA Ames Research Center, published research showing that complex organic compounds were readily produced under conditions that likely prevailed in the early solar system when many meteorites formed.

Meteorites then might have served as the cosmic Mayflowers that transported molecular seeds to Earth. In 1969, the Murchison meteorite that fell in Australia contained dozens of different amino acids—the building blocks of life.

Comets may also have offered a ride to Earth-bound hitchhiking molecules, according to experimental results published in 2001 by a team of researchers from Argonne National Laboratory, the University of California Berkeley, and Lawrence Berkeley National Laboratory. By showing that amino acids could survive a fiery comet collision with Earth, the team bolstered the idea that life’s raw materials came from space.

In 2019, a team of researchers in France and Italy reported finding extraterrestrial organic material preserved in the 3.3 billion-year-old sediments of Barberton, South Africa. The team suggested micrometeorites as the material’s likely source. Further such evidence came in 2022 from samples of asteroid Ryugu returned to Earth by Japan’s Hayabusa2 mission. The count of amino acids found in the Ryugu samples now exceeds 20 different types .

In 1953, UChicago researchers published a landmark paper in the Journal of Biological Chemistry that marked the discovery of the pro-chirality concept , which pervades modern chemistry and biology. The paper described an experiment showing that the chirality of molecules—or “handedness,” much the way the right and left hands differ from one another—drives all life processes. Without chirality, large biological molecules such as proteins would be unable to form structures that could be reproduced.

Today, research on the origin of life at UChicago is expanding. As scientists have been able to find more and more exoplanets—that is, planets around stars elsewhere in the galaxy—the question of what the essential ingredients for life are and how to look for signs of them has heated up.

Nobel laureate Jack Szostak joined the UChicago faculty as University Professor in Chemistry in 2022 and will lead the University’s new interdisciplinary Origins of Life Initiative to coordinate research efforts into the origin of life on Earth. Scientists from several departments of the Physical Sciences Division are joining the initiative, including specialists in chemistry, astronomy, geology and geophysics.

“Right now we are getting truly unprecedented amounts of data coming in: Missions like Hayabusa and OSIRIS-REx are bringing us pieces of asteroids, which helps us understand the conditions that form planets, and NASA’s new JWST telescope is taking astounding data on the solar system and the planets around us ,” said Prof. Ciesla. “I think we’re going to make huge progress on this question.”

Last updated Sept. 19, 2022.

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Extraterrestrial Life Essay

This extraterrestrial life essay is about the search for other life forms on other planets, and whether you think the money spent on this is better spent elsewhere. 

Take a look at the essay question.

Some people believe that using taxpayer funds to look for life on other planets is important. Others, however, think that it is a waste of public money because there are much more important issues requiring funding on our own planet.

Discuss both views and give your opinion.

Understanding the question & brainstorming

The question for this extraterrestrial life essay is fairly straightforward to understand. You need to discuss:

• The pros of looking for life on other planets
• The cons of this (in terms of neglecting important issues on earth)
• Your opinion

It's a bit more of a tricky question though in that you need to come up with some ideas of why it is beneficial to find alternative life. This could involve using some complex language, so you need to be careful with your response.

Dealing with 'Your Opinion'

Remember that you don't have to have a separate body paragraph on ' Your Opinion '. 

A problem that can arise when candidates do this is that they end up with quite short and weak body paragraphs overall as it's difficult to have time to fully explain everything in 40 minutes in three strong body paragraphs.

It can also lead to repetition. Candidates often end up repeating in their opinion paragraph what they have already said in a previous paragraph. 

A solution is to make the second body paragraph your opinion instead, then reiterate this in the conclusion.

Now take a look at the extraterrestrial life essay model answer.

Extraterrestrial Life Essay Sample

You should spend about 40 minutes on this task.

Write about the following topic:

Give reasons for your answer and include any relevant examples from your own experience or knowledge.

Write at least 250 words.

Model Answer

The search for extraterrestrial life has been a topic of discussion and debate for many years. While some people believe that using taxpayer funds to find life on other planets is essential, others see it as a poor use of public money.

Those who believe in the importance of searching for extraterrestrial life argue that this is an opportunity to answer one of the biggest questions in science and human history: are we alone in the universe? They also believe that such a search will have tremendous scientific and technological benefits, including the development of new instruments, techniques, and methods of exploration that can be used for other purposes. Moreover, the discovery of extraterrestrial life, even if only in the form of microbial organisms, would have a profound impact on our understanding of the universe and the origin of life itself.

That said, I personally hold the view that though such research is important, the money spent on this should be balanced against other important needs and should not come at the expense of other critical programs. There are many pressing issues on our own planet that require funding, such as the major problems of poverty, hunger, disease, and environmental degradation. These are all urgent issues that affect millions of people around the world. We need to be mindful of the limited resources available to us and make sure that they are used in a responsible and effective manner.

In conclusion, the search for extraterrestrial life is an important and fascinating endeavour, but it must be balanced against other critical needs. The investment in this area should be used wisely and effectively, taking into account the benefits and limitations of the research, and should not be to the detriment of other important programs.

This extraterrestrial life essay would score highly for IELTS as it clearly answers the question, discussing both sides of the issues and providing the writers opinion. Ideas have supporting evidence and examples. 

It has good coherence and cohesion as it's well-organised into paragraphs and makes use of discourse markers and linking words well.

There are good examples of lexis and collocations, many of which are topic-related. For example:

• tremendous scientific and technological benefits
• development of new instruments, techniques, and methods of exploration
• the form of microbial organisms
• have a profound impact
• origin of life itself

There are also good examples of accurate and effective grammatical forms and sentences. For instance:

• Those who believe in the importance of searching for extraterrestrial life argue that this is an opportunity to answer one of the biggest questions in science and human history.
• ...will have tremendous scientific and technological benefits, including the development of new instruments, techniques, and methods of exploration that can be used for other purposes
• ...the discovery of extraterrestrial life, even if only in the form of microbial organisms, would have ...

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The Search For Life

Whether life exists beyond earth is one of the most profound questions of all time. the answer will change us forever, whether it reveals a universe rich with life, one in which life is rare and fragile, or even a universe in which we can find no other life at all..

The hunt for an answer also is revealing important details about our own place in the universe – where we came from, how life came about and, perhaps, where we’re headed.

The years and decades ahead will bring us ever closer to the ultimate in self-reflection: a mirror image of our own planet Earth. A small, rocky world with clouds, oceans and an atmosphere bearing signs of possible life. This might be a combination of gases – oxygen, carbon dioxide and methane – that, seen by themselves, don't tell us very much, but together speak volumes.

Such a world might be hundreds of light-years away, perhaps forever out of reach. But the molecular evidence we read in its atmosphere, using ever more acute technology, could give us the answer we've awaited since the dawn of humanity: No, we are not alone.

NASA's search for life

The ultimate goal of NASA's Exoplanet Program is to find unmistakable signs of current life.

Exoplanets’ own skies could hold such signs, waiting to be revealed by detailed analysis of the atmospheres of planets well beyond our solar system.

When we analyze light shot by a star through the atmosphere of a distant planet, a technique known as transmission spectroscopy, the effect looks like a barcode. The slices missing from the light spectrum tell us which ingredients are present in the alien atmosphere. One pattern of black gaps might indicate methane, another, oxygen. Seeing those together could be a strong argument for the presence of life. Or we might read a barcode that shows the burning of hydrocarbons; in other words, smog.

Finding another blue and white marble

For a world to have life as we know it, we understand that it would need liquid water on the surface, however, it might not look anything like Earth.

• Largest Batch of Earth-size Habitable Zone Planets Found Orbiting TRAPPIST-1

The planet would most likely exist in the “habitable zone” of the star it orbits, where it is neither too close nor too far from its star. Also called the Goldilock’s zone, this is the area around a star in which liquid water could exist on planets over geological timescales and where its atmosphere could contain the right balance of gases that could support life.

Partners in the search for life

NASA scientists hunting for life beyond Earth form a broad coalition: those investigating our solar system , ancient or extreme life forms on Earth, and even our Sun. Signs of life might be found on Mars, Jupiter's moon Europa or Saturn's moon Enceladus, and potential future missions are in the conceptual or planning stages. Better understanding of early Earth life , or even living "extremophiles," could inform our attempts to detect life beyond our planet. And truly knowing distant exoplanets requires knowledge of the stars they orbit ; greater understanding of our Sun will help us to know other stars.

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Home — Essay Samples — Science — Space Exploration — Aliens And The Probability Of Life On Other Planets

Aliens and The Probability of Life on Other Planets

• Categories: Aliens Space Exploration

About this sample

Words: 1243 |

Published: Mar 18, 2021

Words: 1243 | Pages: 3 | 7 min read

Works Cited

• Arnold, P. (2020, January 7). Scientists Find 60 Potentially Habitable Planets Near Earth. Newsweek. https://www.newsweek.com/scientists-find-60-potentially-habitable-planets-near-earth-1480824
• The Catholic Church and ET Life. (n.d.). SETI Institute. https://www.seti.org/catholic-church-and-et-life
• Hawking, S. (2010). The Grand Design. Bantam Books.
• NASA. (n.d.). Kepler Mission.
• NASA. (n.d.). TESS.
• Roudman, S. (2021, February 5). Scientists are searching for life around these stars. Big Think. https://bigthink.com/space/scientists-are-searching-for-life-around-these-stars
• Scarpino, P. (2019, September 20). A Brief History of Space Exploration. Smithsonian Magazine.
• Spacecraft Cassini-Huygens. (n.d.). NASA.
• United Nations Office for Outer Space Affairs. (n.d.). Space Law.
• Von Daniken, E. (1968). Chariots of the Gods? Unsolved Mysteries of the Past. Tantor Audio.

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Essay on Possibility Of Life On Other Planets

Students are often asked to write an essay on Possibility Of Life On Other Planets in their schools and colleges. And if you’re also looking for the same, we have created 100-word, 250-word, and 500-word essays on the topic.

Let’s take a look…

100 Words Essay on Possibility Of Life On Other Planets

Is there life beyond earth.

Our universe is vast, filled with stars and planets. Scientists believe there might be life on other planets besides Earth. They study space, looking for places that have water and the right temperatures for life.

Searching the Skies

Telescopes help scientists find planets in far-away solar systems. They look for signs that these planets could support life, like having an atmosphere and being not too hot or cold.

Missions to Mars

Mars is our neighbor and has been explored by robots. These robots send back pictures and check if there’s water or signs of past life.

Moons and Beyond

Some moons around other planets might have oceans under their icy surfaces. These hidden seas could be homes for alien creatures.

Life’s Ingredients

Life needs more than water. It needs the right chemicals and energy sources. Scientists are trying to understand what mix might mean life exists somewhere else.

250 Words Essay on Possibility Of Life On Other Planets

Many people wonder if we are alone in the universe or if other planets have living things like us. Scientists are working hard to find the answer. They look at planets and moons to see if they have what life needs to survive.

What Life Needs

All living things on Earth need water, food, and the right temperature to live. So, scientists search for places with water because it’s very important for life. They also look for air that living things can breathe and not too hot or too cold temperatures.

Planets Like Earth

Our Earth is just right for life because it’s not too close or too far from the Sun. This makes the temperature good for water to stay liquid. Scientists have found other planets that are a bit like Earth, in what they call the “Goldilocks Zone.” These planets might have the right conditions for life.

Moons and Microbes

It’s not just planets that could have life. Some moons around other planets have oceans under their icy surfaces. Tiny life forms called microbes might live there. These microbes don’t need sunlight; they can live off chemicals in the water.

Looking for Signs

Spacecraft and telescopes help scientists look for signs of life far away. They can find out what’s in the air of other planets and see if it’s like Earth’s air. They also look for signs of water and chemicals that living things make.

In summary, the possibility of life on other planets is a big question that excites many. With space exploration, we keep searching for answers, hoping to find out if we have neighbors in the vast universe.

500 Words Essay on Possibility Of Life On Other Planets

The universe is huge, with countless stars and planets. For a long time, people have wondered if there are other living things somewhere out there. With new tools and technology, scientists are getting closer to finding an answer.

What Makes a Planet Livable?

To support life as we know it, a planet needs certain things. Water is very important because all living things on Earth need it. The planet should not be too hot or too cold, which means it has to be at just the right distance from its star. This area is called the “Goldilocks Zone.” Also, the air should have gases that living things can breathe.

Scientists use powerful telescopes to look at faraway planets. They are finding many that might have the right conditions for life. These planets are called “exoplanets.” Some of them have signs of water and the right temperature range. This makes them interesting places to look for life.

Robots and Space Probes

Robots and space probes are sent to other planets and moons in our solar system. They take pictures, collect samples, and send back information. Mars, for example, has robots on it right now. These robots are checking if there was ever life there. They look for water, chemicals, and other signs that could mean Mars once had living things.

What Could Alien Life Look Like?

If there is life on other planets, it might be very different from what we see on Earth. It could be tiny bacteria or something we can’t even imagine. The conditions on other planets are not the same as Earth, so life there might have adapted in strange ways.

Challenges in Finding Life

Finding life on other planets is not easy. Space is so big that it takes a long time to get information. Sometimes, the signs of life are hard to spot or could be caused by something else. Scientists have to be very careful and check everything many times.

What Does This Mean for Us?

Thinking about life on other planets is exciting. It can teach us more about our own planet and how life started here. It also makes us think about our place in the universe. Are we alone, or is there a big family of living things out there?

In conclusion, the possibility of life on other planets is a question that makes us curious. With new discoveries and technology, we might find answers someday. Until then, we keep looking up at the stars and wondering.

That’s it! I hope the essay helped you.

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