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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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From soup to cells: The origin of life

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How did life originate?

Living things (even ancient organisms like bacteria) are enormously complex. However, all this complexity did not leap fully-formed from the primordial soup. Instead life almost certainly originated in a series of small steps, each building upon the complexity that evolved previously:

1. Simple organic molecules were formed. Simple organic molecules, similar to the nucleotide shown below, are the building blocks of life and must have been involved in its origin. Experiments suggest that organic molecules could have been synthesized in the atmosphere of early Earth and rained down into the oceans. RNA and DNA molecules — the genetic material for all life — are just long chains of simple nucleotides.

2. Replicating molecules evolved and began to undergo natural selection. All living things reproduce, copying their genetic material and passing it on to their offspring. Thus, the ability to copy the molecules that encode genetic information is a key step in the origin of life — without it, life could not exist. This ability probably first evolved in the form of an RNA self-replicator — an RNA molecule that could copy itself.

Many biologists hypothesize that this step led to an “RNA world” in which RNA did many jobs, storing genetic information, copying itself, and performing basic metabolic functions. Today, these jobs are performed by many different sorts of molecules (DNA, RNA, and proteins , mostly), but in the RNA world, RNA did it all.

Self-replication opened the door for natural selection . Once a self-replicating molecule formed, some variants of these early replicators would have done a better job of copying themselves than others, producing more “offspring.” These super-replicators would have become more common — that is, until one of them was accidentally built in a way that allowed it to be a super-super-replicator — and then, that variant would take over. Through this process of continuous natural selection, small changes in replicating molecules eventually accumulated until a stable, efficient replicating system evolved.

3. Replicating molecules became enclosed within a cell membrane. The evolution of a membrane surrounding the genetic material provided two huge advantages: the products of the genetic material could be kept close by and the internal environment of this proto-cell could be different than the external environment. Cell membranes must have been so advantageous that these encased replicators quickly out-competed “naked” replicators. This breakthrough would have given rise to an organism much like a modern bacterium.

4. Some cells began to evolve modern metabolic processes and out-competed those with older forms of metabolism. Up until this point, life had probably relied on RNA for most jobs (as described in Step 2 above). But everything changed when some cell or group of cells evolved to use different types of molecules for different functions: DNA (which is more stable than RNA) became the genetic material, proteins (which are often more efficient promoters of chemical reactions than RNA) became responsible for basic metabolic reactions in the cell, and RNA was demoted to the role of messenger, carrying information from the DNA to protein-building centers in the cell. Cells incorporating these innovations would have easily out-competed “old-fashioned” cells with RNA-based metabolisms, hailing the end of the RNA world.

5. Multicellularity evolved. As early as two billion years ago, some cells stopped going their separate ways after replicating and evolved specialized functions. They gave rise to Earth’s first lineage of multicellular organisms, such as the 1.2 billion year old fossilized red algae in the photo below.

Where did life originate?

Studying the origin of life

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• INNOVATIONS IN
• 09 May 2018

How Did Life Begin?

• Jack Szostak 0

Jack Szostak is a professor of genetics at Harvard Medical School and one of the recipients of the 2009 Nobel Prize in Physiology or Medicine.

You can also search for this author in PubMed   Google Scholar

Illustration by Chris Gash

Is the existence of life on Earth a lucky fluke or an inevitable consequence of the laws of nature? Is it simple for life to emerge on a newly formed planet, or is it the virtually impossible product of a long series of unlikely events? Advances in fields as disparate as astronomy, planetary science and chemistry now hold promise that answers to such profound questions may be around the corner. If life turns out to have emerged multiple times in our galaxy, as scientists are hoping to discover, the path to it cannot be so hard. Moreover, if the route from chemistry to biology proves simple to traverse, the universe could be teeming with life.

The discovery of thousands of exoplanets has sparked a renaissance in origin-of-life studies. In a stunning surprise, almost all the newly discovered solar systems look very different from our own. Does that mean something about our own, very odd, system favors the emergence of life? Detecting signs of life on a planet orbiting a distant star is not going to be easy, but the technology for teasing out subtle “biosignatures” is developing so rapidly that with luck we may see distant life within one or two decades.

Innovations In The Biggest Questions In Science

To understand how life might begin, we first have to figure out how—and with what ingredients—planets form. A new generation of radio telescopes, notably the Atacama Large Millimeter/submillimeter Array in Chile’s Atacama Desert, has provided beautiful images of protoplanetary disks and maps of their chemical composition. This information is inspiring better models of how planets assemble from the dust and gases of a disk. Within our own solar system, the Rosetta mission has visited a comet, and OSIRIS-REx will visit, and even try to return samples from, an asteroid, which might give us the essential inventory of the materials that came together in our planet.

Once a planet like our Earth—not too hot and not too cold, not too dry and not too wet—has formed, what chemistry must develop to yield the building blocks of life? In the 1950s the iconic Miller-Urey experiment, which zapped a mixture of water and simple chemicals with electric pulses (to simulate the impact of lightning), demonstrated that amino acids, the building blocks of proteins, are easy to make. Other molecules of life turned out to be harder to synthesize, however, and it is now apparent that we need to completely reimagine the path from chemistry to life. The central reason hinges on the versatility of RNA, a very long molecule that plays a multitude of essential roles in all existing forms of life. RNA can not only act like an enzyme, it can also store and transmit information. Remarkably, all the protein in all organisms is made by the catalytic activity of the RNA component of the ribosome, the cellular machine that reads genetic information and makes protein molecules. This observation suggests that RNA dominated an early stage in the evolution of life.

Today the question of how chemistry on the infant Earth gave rise to RNA and to RNA-based cells is the central question of origin-of-life research. Some scientists think that life originally used simpler molecules and only later evolved RNA. Other researchers, however, are tackling the origin of RNA head-on, and exciting new ideas are revolutionizing this once quiet backwater of chemical research. Favored geochemical scenarios involve volcanic regions or impact craters, with complex organic chemistry, multiple sources of energy, and dynamic light-dark, hot-cold and wet-dry cycles. Strikingly, many of the chemical intermediates on the way to RNA crystallize out of reaction mixtures, self-purifying and potentially accumulating on the early Earth as organic minerals—reservoirs of material waiting to come to life when conditions change.

Assuming that key problem is solved, we will still need to understand how RNA was replicated within the first primitive cells. Researchers are just beginning to identify the sources of chemical energy that could enable the RNA to copy itself, but much remains to be done. If these hurdles can also be overcome, we may be able to build replicating, evolving RNA-based cells in the laboratory—recapitulating a possible route to the origin of life.

What next? Chemists are already asking whether our kind of life can be generated only through a single plausible pathway or whether multiple routes might lead from simple chemistry to RNA-based life and on to modern biology. Others are exploring variations on the chemistry of life, seeking clues as to the possible diversity of life “out there” in the universe. If all goes well, we will eventually learn how robust the transition from chemistry to biology is and therefore whether the universe is full of life-forms or—but for us—sterile.

Illustration by Matthew Twombly

Nature 557 , S13-S15 (2018)

doi: https://doi.org/10.1038/d41586-018-05098-w

This article is part of Innovations In The Biggest Questions In Science , an editorially independent supplement produced with the financial support of third parties. About this content .

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The evidence is overwhelming that all life on Earth has evolved from common ancestors in an unbroken chain since its origin. Darwin’s principle of evolution is summarized by the following facts. All life tends to increase: more organisms are conceived, born, hatched, germinated from seed , sprouted from spores, or produced by cell division (or other means) than can possibly survive. Each organism so produced varies, however little, in some measurable way from its relatives. In any given environment at any given time, those variants best suited to that environment will tend to leave more offspring than the others. Offspring resemble their ancestors. Variant organisms will leave offspring like themselves. Therefore, organisms will diverge from their ancestors with time. The term natural selection is shorthand for saying that all organisms do not survive to leave offspring with the same probability. Those alive today have been selected relative to similar ones that never survived or procreated. All organisms on Earth today are equally evolved since all share the same ancient original ancestors who faced myriad threats to their survival. All have persisted since roughly 3.7 billion to 3.5 billion years ago during the Archean Eon (4 billion to 2.5 billion years ago), products of the great evolutionary process with its identical molecular biological bases. Because the environment of Earth is so varied, the particular details of any organism’s evolutionary history differ from those of another species in spite of chemical similarities.

Everywhere the environment of Earth is heterogeneous . Mountains, oceans, and deserts suffer extremes of temperature, humidity, and water availability. All ecosystems contain diverse microenvironments: oxygen-depleted oceanic oozes, sulfide- or ammonia-rich soils, mineral outcrops with a high radioactivity content, or boiling organic-rich springs, for example. Besides these physical factors, the environment of any organism involves the other organisms in its surroundings. For each environmental condition, there is a corresponding ecological niche . The variety of ecological niches populated on Earth is quite remarkable. Even wet cracks in granite are replete with “rock eating” bacteria . Ecological niches in the history of life have been filled independently several times. For example, quite analogous to the ordinary placental mammalian wolf was the marsupial wolf, the thylacine (extinct since 1936) that lived in Australia; the two predatory mammals have striking similarities in physical appearance and behaviour. The same streamlined shape for high-speed marine motion evolved independently at least four times: in Stenopterygius and other Mesozoic reptiles; in tuna , which are fish; and in dolphins and seals , which are mammals. Convergent evolution in hydrodynamic form arises from the fact that only a narrow range of solutions to the problem of high-speed marine motion by large animals exists. The eye , a light receptor that makes an image, has evolved independently more than two dozen times not only in animals on Earth but in protists such as the dinomastigote Erythropsodinium . Apparently eyelike structures best solve the problem of visual recording. Where physics or chemistry establishes one most efficient solution to a given ecological problem, evolution in distinct lineages will often tend toward similar, nearly identical solutions. This phenomenon is known as convergent evolution .

Life ultimately is a material process that arose from a nonliving material system spontaneously—and at least once in the remote past. How life originated is discussed below. Yet no evidence for spontaneous generation now can be cited. Spontaneous generation, also called abiogenesis , the hypothetical process by which living organisms develop from nonliving matter, must be rejected. According to this theory, pieces of cheese and bread wrapped in rags and left in a dark corner were thought to produce mice, because after several weeks mice appeared in the rags. Many believed in spontaneous generation because it explained such occurrences as maggots swarming on decaying meat.

By the 18th century it had become obvious that plants and animals could not be produced by nonliving material. The origin of microorganisms such as yeast and bacteria, however, was not fully determined until French chemist Louis Pasteur proved in the 19th century that microorganisms reproduce, that all organisms come from preexisting organisms, and that all cells come from preexisting cells. Then what evidence is there for the earliest life on Earth?

Past time on Earth, as inferred from the rock record, is divided into four immense periods of time called eons. These are the Hadean (4.6 billion to 4 billion years ago), the Archean (4 billion to 2.5 billion years ago), the Proterozoic (2.5 billion to 541 million years ago), and the Phanerozoic (541 million years ago to the present). For the Hadean Eon, the only record comes from meteorites and lunar rocks. No rocks of Hadean age survive on Earth. In the figure , eons are divided into eras, periods, and epochs. Such entries in the geologic time scale are often called “geologic time intervals.”

Among the oldest known fossils are those found in the Fig Tree Chert from the Transvaal, dated over three billion years ago. These organisms have been identified as bacteria, including oxygenic photosynthetic bacteria (cyanobacteria)—i.e., prokaryotes rather than eukaryotes. Even prokaryotes, however, are exceedingly complicated organisms that grow and reproduce efficiently. Structures of communities of microorganisms, layered rocks called stromatolites , are found from more than three billion years ago. Since Earth is about 4.6 billion years old, these finds suggest that the origin of life must have occurred within a few hundred million years of that time.

Chemical analyses on organic matter extracted from the oldest sediments show what sorts of organic molecules are preserved in the rock record. Porphyrins have been identified in the oldest sediments, as have the isoprenoid derivatives pristane and phytane, breakdown products of cell lipids. Indications that these organic molecules dating from 3.1 billion to 2 billion years ago are of biological origin include the fact that their long-chain hydrocarbons show a preference for a straight-chain geometry. Chemical and physical processes alone tend to produce a much larger proportion of branched-chain and cyclic hydrocarbon molecular geometries than those found in ancient sediments. Nonbiological processes tend to form equal amounts of long-chain carbon compounds with odd and even numbers of carbon atoms. But products of undoubted biological origin, including the oldest sediments, show a distinct preference for odd numbers of carbon atoms per molecule . Another chemical sign of life is an enrichment in the carbon isotope C 12 , which is difficult to account for by nonbiological processes and which has been documented in some of the oldest sediments. This evidence suggests that bacterial photosynthesis or methanogenesis, processes that concentrate C 12 preferentially to C 13 , were present in the early Archean Eon.

The Proterozoic Eon, once thought to be devoid of fossil evidence for life, is now known to be populated by overwhelming numbers of various kinds of bacteria and protist fossils—including acritarchs (spherical, robust unidentified fossils) and the entire range of Ediacaran fauna . The Ediacarans—large, enigmatic , and in some cases animal-like extinct life-forms—are probably related to extant protists. Almost 100 species are known from some 30 locations worldwide, primarily sandstone formations. Most Ediacarans, presumed to have languished in sandy seaside locales, probably depended on their internal microbial symbionts (photo- or chemoautotrophs ) for nourishment . No evidence that they were animals exists. In addition to the Ediacarans, acritarchs, and other abundant microfossils, clear evidence for pre-Phanerozoic, or Precambrian, life includes the massive banded-iron formations (BIFs). Most BIFs date from 2.5 billion to 1.8 billion years ago. They are taken as indirect evidence for oxygen-producing, metal-depositing microscopic Proterozoic life. Investigations that use the electron microprobe (an instrument for visualizing structure and chemical composition simultaneously) and other micropaleontological techniques unfamiliar to classical geology have been employed to put together a much more complete picture of pre-Phanerozoic life.

The earliest fossils are all of aquatic forms. Not until about two billion years ago are cyanobacterial filaments seen that colonized wet soil . By the dawn of the Phanerozoic Eon, life had insinuated itself between the Sun and Earth, both on land and in the waters of the world. For example, the major groups of marine animals such as mollusks and arthropods appeared for the first time about 541 million years ago at the base of the Cambrian Period of the Phanerozoic Eon. Plants and fungi appeared together in the exceptionally well-preserved Rhynie Chert of Scotland, dated about 408 million–360 million years ago in the Devonian Period . Solar energy was diverted to life’s own uses. The biota contrived more and more ways of exploiting more and more environments . Many lineages became extinct. Others persisted and changed. The biosphere’s height and depth increased, as did, by implication , the density of living matter. The proliferation and extinctions of a growing array of life-forms left indelible marks in the sedimentary rocks of the biosphere ( see evolution: The concept of natural selection ).

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How did life begin?

Some things are alive and some things are not. Seems like an easy and obvious concept, but drawing the line that separates “alive” from “not alive” is not quite as straightforward as you might think. What makes something alive? Well, if you Google “properties of life,” you will see that there are seven (or eight, or nine, or maybe even ten) things that everyone “agrees” are key—things like growth, the ability to reproduce, response to stimuli and the environment, maintaining homeostasis, and, often, cellular organization.

So, a quick quiz.  A rock? Not alive. An oak tree? Alive. Water? Not alive. Single-celled bacteria? Alive. An RNA virus? Well, now things get interesting.

Most viruses are simple. They are composed of an outer shell or membrane that surrounds some genetic material: sometimes DNA, sometimes RNA, sometimes both. They generally can’t, however, reproduce on their own—one of the essential properties of life. Instead, they co-opt the reproduction machinery of the cells they infect, making the cell make more viruses. So, there is some disagreement among scientists about whether viruses count as alive or not, but because they contain genetic material, they are, at least, likely to be related to other life on Earth. All life that we know of shares the use of DNA or RNA to carry genetic information, which suggests a shared origin; viruses are somehow connected to the evolutionary tree of life—which brings us to a second line between life and no life.

If we think about the history of the Earth, at some point in the past there was no life and now the place is practically bursting at the seams with it. How did that happen? That is a question that has perplexed humanity for millennia. Two Eberly College of Science researchers have brought the diverse expertise of their labs together to explore some possible answers.

Life in its simplest form could be thought of as a collection of molecules that perform chemical reactions and that are somehow compartmentalized, isolating them from their environment. Christine Keating , professor of chemistry, studies physical chemistry and the self-assembly of molecules. As an undergrad she studied chemistry and biology, so she gravitated toward studying the materials chemistry of life and how cells might have evolved. Phil Bevilacqua , head of the Department of Chemistry and Distinguished Professor of Chemistry and of Biochemistry and Molecular Biology, has been studying RNA for nearly 30 years. RNA can both carry genetic information and perform chemical reactions, making it an attractive candidate for playing a role in early life.

“There was this old Reese’s Peanut Butter Cup commercial where one person had chocolate and another had peanut butter and they bumped into each other,” said Keating. “The chocolate got into the peanut butter and they were like, ‘This is amazing.’ I think of our collaboration like one of us had the chocolate and one of us had the peanut butter. Our research really complements each other’s to be able to look at possible scenarios for the evolution of early life.”

It’s an RNA world

Or at least it was. Maybe.

“How life actually began is basically unknowable,” said Bevilacqua. “There is no fossil record of the early steps that led to life, and we can’t go back to observe what was going on. What we can do, though, is use what we know about the Earth three to four billion years ago and what we know about the simplest forms of life to build models and test hypotheses. We can begin to narrow down what might have been possible and eliminate ideas that probably aren’t.”

One of the leading hypotheses about the origin of life on Earth leans heavily on the role of RNA. RNA is DNA’s lesser known little brother; it stands for ribonucleic acid (DNA is deoxyribonucleic acid ). Both molecules are long strings composed of four basic subunits, and it’s the sequence of these units that encodes genetic information.

The four subunits of DNA are adenine, thymine, cytosine, and guanine; they are called nucleotides or bases, but we often just refer to them as A, T, C, and G. The DNA molecule is double stranded. Think of a twisted ladder: The side rails of the ladder are the two strands, and the rungs represent the bonds that hold them together. The two strands are complementary to each other: If there is an A on one side of the rung, the other side will have a T; and if there is a C on one side, the other will have a G.

RNA shares three of the four subunits with DNA but has uracil (U) instead of thymine (T) and is single stranded. Because sections of the RNA molecule can be complementary to other sections, the molecule can fold up on itself, bonding in a way similar to double-stranded DNA, with U complementing A. The resulting three-dimensional structures of RNA molecules can allow it to do more than just encode information; it can carry out functions that are nowadays mostly associated with proteins.

“RNA became implicated in early life scenarios in the late 1960s,” said Bevilacqua. “It was recognized that the complex structures that RNA forms could potentially perform catalysis—it could drive chemical reactions. So, you have a single molecule that sort of solved the ‘chicken and egg’ question of which came first in the origin of life: genetic information or catalysis? Work in the 1980s that led to a Nobel Prize demonstrated that RNA can in fact do both, so it became a prime candidate for how early life could have evolved in what is known as the RNA world hypothesis .”

The research in Bevilacqua’s lab focuses on understanding the functions of RNA at the molecular level. His group studies the mechanisms of RNA enzymes—RNA molecules that have functions similar to protein enzymes in chemical reactions—known as ribozymes . Their research helped to establish the role played by ribozymes in proton transfer and RNA cleavage, and they are currently studying the role of metal ions and other cofactors in these mechanisms. They also study the precise mechanisms of how RNA molecules fold in cells. Studying the role of RNA in early life came later.

“Because I work on RNA catalysis, I’ve always been interested in its potential role in early life, but I never took it too seriously,” said Bevilacqua. “It would come up as the last sentence of a discussion in a paper: ‘This versatility of RNA to perform reactions could relate to the RNA world hypothesis.’ But in thinking of what it would take to go from a bunch of molecules floating around with the ability to perform reactions to something that could be called early life, I started to work with Chris, putting together her expertise in protocells with my expertise in RNA.”

Compartmentalize it!

If you think about a modern cell with its hundreds of components—organelles, proteins, DNA, and RNA—working together seamlessly to perform its varied functions, it can be hard to imagine how it could have evolved. But we know that it must have. Before there were modern cells, there had to be earlier, simpler ones. And before that, there had to exist the components to form them.

We can imagine an early, prelife Earth in which chemical reactions are occurring that begin to produce molecules that resemble things like RNA. But even if these early molecules could potentially encode genetic information and perform catalysis, they would be floating around in the proverbial primordial soup, and the chance they would find each other and actually do these things seems incredibly slim. A necessary step, therefore, in the early evolution of what would become life was to increase the chances that these molecules would come together where they could begin to interact in more and more-complex ways. One way to do that was to compartmentalize them.

“We were studying the self-assembly of molecules, what molecules can do on their own, and it’s kind of amazing what you get for free,” said Keating. “An example is lipid self-assembly. Lipids are fatty compounds that are insoluble in water. If you have some lipids and you add water—boom! Vesicles form. It’s amazing to watch.”

Among other things, Keating’s group studies artificial cells. Somewhat counterintuitively, she decided to start by recreating the cell’s cytoplasm—the goo on the inside that is often ignored—rather than its membrane. Even without membranes, you could get compartments through liquid-liquid phase separation.

“We always knew that if we were going to make artificial cells, it needed to be in a way that we could learn about real cells,” said Keating. “So, starting with the cytoplasm—where everything within the cell takes place—made sense, even though people may think it’s the boring part. We were kind of amazed at how quickly things got interesting.”

Macromolecules (big molecules—like RNA, for example) would concentrate into different liquid phases within the artificial cytoplasm.

“Without really trying, we found a solution to one of the big problems in studying the origin of life, which is, ‘How do you put stuff in your compartment?’” said Keating. “You can make a membrane really easily, like with lipids, but it’s incredibly difficult to get things inside of them. With our system, you get these phase-separated droplets—called coacervates —in which macromolecules collect, and you can concentrate them from a really dilute solution. What better to study in this system than RNA, which is where Phil comes in.”

Two great tastes that taste great together

“Working with Chris, we really started to think about how it all began, how did life start, how do you compartmentalize molecules to facilitate the types of reactions we were studying,” said Bevilacqua. “We began to look at what’s possible, and not only that but what would be feasible and probable. I was coming from one angle and she was coming from another, and there was a confluence of our two approaches that really made sense.”

The collaboration is already paying dividends. Recently, the two groups published a paper demonstrating that not only could RNA be assembled from its constituent parts inside of membraneless compartments but the concentration of the RNAs in the compartments also enhanced the enzymatic activity of ribozymes.

Whether or not these particular steps actually took place during life’s evolution on Earth, the collaboration of Keating’s and Bevilacqua’s research groups is advancing our understanding of what might have happened. They go together like chocolate and peanut butter.  

“I’d like to lay claim to being the chocolate in the Reese’s cup,” said Keating.

August 1, 2017

How Did Life Begin on Earth?

By Mariette DiChristina

Life on Earth could have arisen in places similar to the Grand Prismatic Spring in Yellowstone National park.

Getty Images

There was light. But then what happened?

How did life arise on the third rocky planet orbiting the unremarkable star at the center of our solar system? Humans have been wondering about the answer to that question probably almost as long as we've been able to wonder. In recent decades scientists have made some gains in understanding the conceivable mechanisms, gradually settling on a possible picture of our origins in the oceans. The idea was that hydrothermal vents at the bottom of the seas, protected from cataclysms rending the surface four billion years ago, delivered the necessary energy and could have sustained the molecules needed.

Perhaps not. Water was a necessary ingredient, surely, but that doesn't mean we sprang from oceans, according to researchers Martin J. Van Kranendonk, David W. Deamer and Tara Djokic in our cover story, “ Life Springs .” Oceans, they write, might have spread the needed molecules too quickly for cell membranes and functions to occur. Instead they argue, land pools in an active volcanic landscape that repeatedly dried and got wet again could have cradled the seeds of life. How could something that sounds so harsh have been beneficial, you ask? Read the article to find out.

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The sun's rays provided vitality for this world. Seeing them dim temporarily, as they do during a solar eclipse, is awe-inspiring. It's been nearly a century since a total solar eclipse has crossed the U.S. from coast to coast. You'll find that “ The Great Solar Eclipse of 2017 ,” by Jay M. Pasachoff, tells you everything you need to know about this rare event. And a companion piece, “ 1,000 Years of Solar Eclipses ,” by senior editor Mark Fischetti, with illustrations by senior graphics editor Jen Christiansen and designer Jan Willem Tulp, tells you what you will need to know as well. I like to think that the readers of Scientific American , which turns 172 this month, will be enjoying the solar shows well into the future.

If they do enjoy them, it'll be because we've fostered a love of learning about the world around us. How we teach and create the right learning environments are critical to our students' success. For that reason, we've taken an evidence-based look at the concept of vouchers in education in “ A Matter of Choice ,” by journalist Peg Tyre. The concept is a keystone of the current administration's plan to revamp education, but research finds it wanting. Fortunately, there is still time to make a choice.

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How Did Life Begin?

Even before Charles Darwin proposed his theory of evolution in 1859, scientists the world over had been trying to understand how life got started. How did non-living molecules that covered the young Earth combine to form the very first life form?

Chemist Nicholas Hud has been working on this problem at the Georgia Institute of Technology for more than a decade. He and his students have discovered that small molecules could have acted as "molecular midwives" in helping the building blocks of life's genetic material form long chains, and may have assisted in selecting the base pairs of the DNA double helix.

The discovery is an important step in the effort to trace the evolution of life all the way to the very beginning, back to the earliest self-replicating molecules.

"We are working to uncover how molecules similar to RNA and DNA first appeared on Earth around 4 billion years ago," Hud said. "A few years ago, we proposed a theory that small, simple molecules acted as templates for the production of the first RNA-like molecules. Many of these small molecules, or molecular midwives, would have worked together to produce RNA by spontaneously mixing and assembling with the chemical building blocks of RNA."

In contemporary life, RNA is present in all cells and is responsible for transmitting genetic information from DNA to proteins. Many scientists believe that RNA, or something similar to RNA, was the first molecule on Earth to self-replicate and begin the process of evolution that led to more advanced forms of life, including human beings.

Recently, Hud and his team made a discovery that further advances their theory that certain molecules helped the first RNA and DNA molecules to form.

"We've found that the molecule ethidium can assist short polymers of nucleic acids, known as oligonucleotides, in forming longer polymers. Ethidium can also select the structure of the base pairs that hold together two strands of DNA."

One of the biggest problems in getting a polymer to form is that, as it grows, its two ends often react with each other instead of forming longer chains. The problem is known as strand cyclization. Hud and his research team discovered that by using a molecule that can bind in between two neighboring base pairs of DNA, known as an intercalator, they can bring short pieces of DNA and RNA together in a manner that helps them create much longer molecules.

"If you have the intercalator present, you can get polymers. With no intercalator, it doesn't work, it's that simple," Hud explained.

Hud and his team also tested how much influence a midwife molecule might have had on creating the Watson-Crick base pairs that make up the structure of DNA (A pairs with T, and G pairs with C). They found that the base pair matching was dependent on the midwife present during the reaction. Ethidium was most helpful for forming polymers with the specific Watson-Crick base pairs of DNA. Another molecule that they call aza3 made polymers in which each A base is paired with another A.

"In our experiment, we found that the midwife molecules we used had a direct effect on the kind of base pairs that formed," Hud said. "We're not saying that ethidium was the original midwife, but we've shown that the principle of a small molecule working as a midwife is sound."

"We're now searching for the identity of a molecule that could have helped make the first genetic polymers, a sort of 'unselfish' molecule that was not part of the first genetic polymers, but was critical to their formation," he added.

-- David Terraso, Georgia Institute of Technology, [email protected]

This Behind the Scenes article was provided to LiveScience in partnership with the National Science Foundation.

Related links

• LiveScience.com: Behind the Scenes: How Did Life Begin?
• Uncovering Life's Beginnings: Georgia Tech Awarded a $20M Center for Chemical Innovation

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We now know that life began on Earth much earlier than we thought

A big rethink of our planet’s early years adds to growing fossil, chemical and DNA evidence that Earth was only a few hundred million years old when life began

By Penny Sarchet

21 August 2024

The oldest known piece of Earth? A 4.4 billion-year-old zircon

John Valley, University of Wisconsin-Madison

Until recently, many discounted the idea that life could have existed on Earth before 3.8 billion years ago because it was thought that heavy pummelling from asteroids would have made this impossible. But several lines of evidence are pointing to an earlier origin of life , and as we begin to question whether the late heavy bombardment really happened at all, it’s beginning to look like life started surprisingly early in our planet’s history.

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How Did Life Begin?

How life came from non-life is still largely a scientific mystery.

Structure of a variety of membrane proteins

Introduction

Despite how much we know about the state of the Earth 3–4 billion years ago and the complexity of the building blocks of life—DNA, RNA, amino acids, sugars—no entirely plausible scientific explanation for the spontaneous origin of life has been found. How life came from non-life, or abiogenesis, is still largely a scientific mystery.

Because the topic does not have as many potentially useful applications as other areas of science, less research has been performed in this area. However, scientists are currently approaching this challenge from a number of different perspectives, and it is possible that broad consensus will emerge in the future. 1

God could have created the first life through regular processes, or God could have done a  miracle . In either case, BioLogos affirms that God is the creator and sustainer of all life, from the first life form to each of us.  If consensus for a particular scientific explanation emerges, we will celebrate, because we will have more insight into God’s handiwork. Yet no matter how far science progresses, we can never exhaust the wonder and gratitude we feel for God’s good gift of life.

The first life on Earth

In discussions about the origin of life, an important first step is clarifying what is meant by life. The first forms of life on Earth were probably very different from what we would call life today. It may be tempting to think of life as anything containing the DNA double helix so familiar to us. However, the main property required for early life is self-replication. The earliest self-replicating systems could have been made out of DNA, RNA, or some other basic building blocks. The key feature of such systems would have to be the ability to gather chemicals from the local environment and make copies of themselves.

All life on Earth contains carbon as an essential elemental building block. 2  Carbon is the simplest element capable of forming the remarkably complex molecules that are so prevalent in life forms. Therefore, it is likely that carbon was involved from the beginning. Compounds containing carbon are generally categorized as organic; and exploring the natural mechanisms that create complex organic compounds is a main focus in research on the origins of life.

The Earth is approximately 4.6 billion years old . All evidence suggests that the Earth was inhospitable to life for the first 700 million years, largely because it was so hot. However, the Earth gradually cooled, and 4 billion years ago it became more hospitable. Within little more than 100 million years, the first single-cell life forms appeared. 3  Where did these organisms come from? And what were their capabilities?

Although we do not know the path that led to these early bacterial forms, it seems likely that DNA had emerged as the information molecule by this time. Microbiologist and physicist Carl R. Woese suggests there was a considerable amount of lateral gene transfer among the first forms of bacteria called archaebacteria. 4  Lateral gene transfer, which is the movement of genes from one bacterium to another, would have enabled the exchange of genetic material, and it would therefore expedite the process of diversification of biological function acted upon by natural selection. How these first organisms ever developed in the first place is the topic of the following discussion.

The Miller-Urey experiment

Charles Darwin is often credited for the original “warm little pond” hypothesis, which proposes life may have formed from a combination of inorganic compounds and energy. 5  Soviet biochemist Aleksandr Ivanovich Oparin revisited this idea and proposed life formed in an environment that lacked oxygen but was energized by sunlight. 6  These kinds of ideas are the basis of much research of life’s origins, including the famous Miller-Urey experiment.

In 1953 at the University of Chicago, Stanley Miller and Harold Urey tackled the problem of the origin of life by reproducing the conditions they believed to be present on the primitive Earth when life originated. By zapping a mixture of water and inorganic compounds with electricity, they produced organic compounds including amino acids, the building blocks of protein. 7  This result catalyzed further experiments—and at least to some, it appeared that the solution to life’s mystery was about to unfold.

Recently, these initial results were revisited with more sensitive methods. Researchers discovered additional amino acids and other building blocks formed during the Miller-Urey experiments that they originally had not realized. 10  Miller continued a variety of experiments to pin down life’s origins and, though the mystery remained unsolved, members of his lab discovered amino acids and other building blocks for life can also form from inorganic compounds in extremely cold environments. 11

How life came together

Explanations of how the amino acids, nucleotides, and sugars were formed, how they assembled in the form of DNA and RNA, and then how these building blocks of life came to replicate themselves and acquire the enzymes to facilitate this process, are all still speculative. Many interesting ideas are being researched, however, including the deep sea vent theory, 12  radioactive beach theory 13  and crystal or clay theory. 14 Another opinion, held by Francis Crick and others, is that the only explanation for life on Earth is that it came from another planet. 15  However, this type of explanation only pushes the question farther back: How did this extraterrestrial life originate? A compelling scientific explanation of the origin of life here on Earth has not yet emerged.

Evolutionary theories of how life originated fall in two main camps: the gene first hypothesis and the metabolism first hypothesis. The gene first hypothesis currently focuses on RNA rather than DNA, as certain RNA molecules have shown the ability to function as enzymes, suggesting RNA could have both carried information and copied itself. From this point of view, RNA preceded both DNA and protein synthesis. On the other hand, the metabolism first hypothesis argues the molecules of prebiotic materials formed chemical cycles and networks of chemical reactions that gave rise to primitive metabolic systems. These metabolic systems existed before RNA and provided the environment for RNA replication to later emerge. Despite the exploration of numerous avenues of research, both theories currently lack conclusive evidence.

While researchers have recently generated self-replicating RNA from prebiotic molecules in the laboratory, 16  it is difficult to understand how RNA—a notoriously unstable polymer—could have supported self-replicating systems in the hostile chemical and thermal environment of early planet Earth.

Regardless of how, it is clear that life did emerge, and the first life forms were single-celled organisms that began to replicate and diversify. The lack of scientific consensus on the origin of life does not diminish the strength of  evolutionary theory , which only seeks to explain the diversity of life forms after life had already begun.

Although the origin of life is certainly a genuine scientific mystery, this is not the place for thoughtful people to wager their faith. All that has happened in the history of life has happened according to God’s sovereign purposes, and Christ “is before all things, and in him all things hold together” (Col. 1:17).

• Two examples of research groups working on the topic are the Joyce Lab at the Scripps Research Institute and Jack Szostak’s  The Origins of Life initiative at Harvard University .  Recommended books on the subject include Robert M. Hazen, Genesis:  The Scientific Quest for Life’s Origins  (Washington, D.C.: Joseph Henry Press, 2005), and Andrew H. Knoll  Life on a Young Planet: The First Three Billion Years of Evolution on Earth  (New Jersey: Princeton University Press, 2003).
• It has been hypothesized that silicon may be an alternative to carbon, as it is structurally similar to carbon with a half filled outer shell and four free electrons. As of yet it has not been shown to be a  viable alternative  because of differences in the way it reacts to other molecules.
• Heinrich D. Holland, “Evidence for Life on Earth More Than 3850 Million Years Ago,”  Science  275, no. 3 (1997): 38-39.
• Carl Woese, “The Universal Ancestor,”  Proceedings of the National Academy of Sciences  95, no. 12 (1998): 6854-9.  See also W. Ford Doolittle, “Uprooting the Tree of Life,”  Scientific American  282, no. 2 (2000): 90.
• Francis Darwin, ed.,  The Life and Letters of Charles Darwin, Including an Autobiographical Chapter  (London: John Murray, 1887), 3:18. Available online at Darwin Online, “ The Complete Works of Charles Darwin Online ,” Darwin Online.
• Aleksandr I. Oparin,  The Origin of Life  (New York: Dover, 1952).
• Stanley L. Miller, “A Production of Amino Acids under Possible Primitive Earth Conditions,”  Science 117 (1953): 528–9.
• Joan Oro, “Mechanism of synthesis of adenine from hydrogen cyanide under possible primitive Earth conditions,”  Nature  191 (1961): 1193–4.
• Michael P. Robertson and Stanley L. Miller, “An Efficient Prebiotic Synthesis of Cytosine and Uracil,” Nature  375 (1995): 772-4.
• Adam P. Johnson et al., “The Miller Volcanic Spark Discharge Experiment,”  Science  322, no. 5900 (2008): 404.
• Douglas Fox, “ Did Life Evolve in Ice? ”  Discover Magazine  (2008), and M. Levy et al, “Prebiotic Synthesis of Adenine and Amino Acids under Europa-like Conditions,”  Icarus  145, no. 2 (2000): 609–13.
• W. Martin and M.J. Russell M.J, “On the Origins of Cells: A Hypothesis for the Evolutionary Transitions from Abiotic Geochemistry to Chemoautotrophic Prokaryotes, and from Prokaryotes to Nucleated Cells,” Philosophical Transactions of the Royal Society: Biological Sciences  358 (2003): 59-85, and Jianghai Li and Timothy M. Kusky, “World’s Largest Known Precambrian Fossil Black Smoker Chimneys and Associated Microbial Vent Communities, North China: Implications for Early Life,”  Godwana Research  12 (2007): 84-100.
• Adam, Zachary, “Actinides and Life’s Origins,”  Astrobiology  7, no. 6 (2007): 852–872.
• Martin M. Hanczyc, Shelly M. Fujikawa and Jack W. Szostak, “Experimental Models of Primitive Cellular Compartments: Encapsulation, Growth, and Division,”  Science  302, no. 5654 (2003): 618-622.
• Francis Crick,  Life Itself: Its Origin and Nature  (New York: Simon and Schuster, 1981).
• Carl Zimmer, “On the Origin of Life on Earth,”  Science  323 (2009).

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7 theories on the origin of life

The answer to the origin of life remains unknown, but here are scientists best bets

• An electric spark

Molecules of life met on clay

• Deep-sea vents
• Born from ice
• Understanding DNA
• Simple beginnings
• Life came from space

Additional resources

Bibliography.

The origin of life on Earth began more than 3 billion years ago, evolving from the most basic of microbes into a dazzling array of complexity over time. But how did the first organisms on the only known home to life in the universe develop from the primordial soup?

Science remains undecided and conflicted as to the exact origin of life, also known as abiogenesis. Even the very definition of life is contested and rewritten, with one study published in the J ournal of Biomolecular Structure and Dynamics , suggesting uncovering 123 different published definitions. 

Although science still seems unsure, here are  some of the many different scientific theories on the origin of life on Earth.

It started with an electric spark

Lightning may have provided the spark needed for life to begin.Electric sparks can generate amino acids and sugars from an atmosphere loaded with water, methane, ammonia and hydrogen , as was shown in the famous Miller-Urey experiment  in 1952, according to Scientific American . The experiment's findings  suggested that lightning might have helped create the key building blocks of life on Earth in its early days. Over millions of years, larger and more complex molecules could form. 

Although research since then has revealed the early atmosphere of Earth was actually hydrogen-poor, scientists have suggested that volcanic clouds in the early atmosphere might have held methane, ammonia and hydrogen and been filled with lightning as well, according to the University of California

The first molecules of life might have met on clay, according to an idea elaborated by organic chemist Alexander Graham Cairns-Smith at the University of Glasgow in Scotland. Cairns-Smith proposed in his 1985 controversial book “ Seven Clues to the Origin of Life'' , that clay crystals preserve their structure as they grow and stick together to form areas exposed to different environments and trap other molecules along the way and organise them into patterns much like our genes do now.

– What is the difference between prokaryotic and eukaryotic cells?

– What is biology?

– What are bacteria?

– What is an amoeba?

– Is there water on Mars?

The main role of DNA is to store information on how other molecules should be arranged. Genetic sequences in DNA are essentially instructions on how amino acids should be arranged in proteins. Cairns-Smith suggests that mineral crystals in clay could have arranged organic molecules into organized patterns. After a while, organic molecules took over this job and organized themselves.

Although Cairns-Smith's theory certainly gave scientists food for thought in the 1980s, it has still not been widely accepted by the scientific community.

Life began at deep-sea vents

The deep-sea vent theory suggests that life may have begun at submarine hydrothermal vents spewing elements key to life, such as carbon and hydrogen-, according to the journal Nature Reviews Microbiology .

Hydrothermal vents can be found in the darkest depths of the ocean floors, typically on diverging continental plates, according to the Natural History Museum . These vents erupt fluid which is superheated by the Earth’s core as it passes up through the crust, before being ejected at the vets. During its journey through the crust it collects dissolved gases and minerals, such as carbon and hydrogen. 

Their rocky nooks could then have concentrated these molecules together and provided mineral catalysts for critical reactions. Even now, these vents, rich in chemical and thermal energy, sustain vibrant ecosystems.

Abiogenesis by way of hydrothermal vents continues to be investigated as a plausible cause of life on Earth. In 2019, scientists at University College London , successfully created protocells (non-living structures that help scientists understand the origins of life) under similar hot, alkaline environmental conditions to hydrothermal vents.

Life had a chilly start

Ice might have covered the oceans 3 billion years ago and facilitated the birth of life. "Key organic compounds thought to be important in the origin of life are more stable at lower temperatures,” Jeffrey Bada at the University of California, told New Scientist . At normal temperatures these compounds, such as simple sets of amino acids, are sparsely populated in water, but when frozen become concentrated and facilitate the emergence of life, according to Bada’s work published in the journal I carus .  

Ice also might have protected fragile organic compounds in the water below from ultraviolet light and destruction from cosmic impacts. The cold might have also helped these molecules to survive longer, enabling key reactions to happen. 

The answer lies in understanding DNA formation

Nowadays DNA needs proteins in order to form, and proteins require DNA to form, so how could these have formed without each other? The answer may be RNA , which can store information like DNA, serve as an enzyme like proteins, and help create both DNA and proteins, according to the journal Molecular Biology of the Cell . Later DNA and proteins succeeded this "RNA world," because they are more efficient.

RNA still exists and performs several functions in organisms, including acting as an on-off switch for some genes. The question still remains how RNA got here in the first place. Some scientists think the molecule could have spontaneously arisen on Earth, while others say that was very unlikely to have happened. 

Life had simple beginnings

Instead of developing from complex molecules such as RNA, life might have begun with smaller molecules interacting with each other in cycles of reactions. These might have been contained in simple capsules akin to cell membranes, and over time more complex molecules that performed these reactions better than the smaller ones could have evolved, scenarios dubbed "metabolism-first" models, as opposed to the "gene-first" model of the "RNA world" hypothesis.

Life was brought here from elsewhere in space

Perhaps life did not begin on Earth at all, but was brought here from elsewhere in space, a notion known as panspermia, according to NASA . For instance, rocks regularly get blasted off Mars by cosmic impacts, and a number of Martian meteorites have been found on Earth that some researchers have controversially suggested brought microbes over here, potentially making us all Martians originally. Other scientists have even suggested that life might have hitchhiked on comets from other star systems. However, even if this concept were true, the question of how life began on Earth would then only change to how life began elsewhere in space.

For more information into the theories of life’s origins check out “ The Stairway To Life: An Origin-Of-Life Reality Check ” by Change Laura Tan and “ The Mystery of Life's Origin ” by Charles B. Thaxton, et al. 

Matthew Levy et al, “Prebiotic Synthesis of Adenine and Amino Acids Under Europa-like Conditions”, Icarus, Volume 145, June 2000, https://doi.org/10.1006/icar.2000.6365

William Martin, “Hydrothermal vents and the origin of life”, Nature Reviews Microbiology, Volume 6, September 2008, https://doi.org/10.1038/nrmicro1991  

K. A. Dill and L. Agozzino, “Driving forces in the origins of life”, Open biology, Volume 11, February 2021, ttps://doi.org/10.1098/rsob.200324 

Ben K. D. Pearce et al, “Origin of the RNA world: The fate of nucleobases in warm little ponds”, PNAS, Volume 114, October 2017, https://doi.org/10.1073/pnas.1710339114

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5. How have life and Earth co-evolved?

5.1. how did life first emerge on earth.

Grades K-2 or Adult Naive Learner

• NGSS Connections for Teachers
• Concept Boundaries for Scientists

Have you ever had a mystery to solve? Like a time when you knew something happened, but you didn’t really know how? Maybe you felt like you needed to find some clues to figure out what happened. That’s how scientists feel about figuring out how life got going here on Earth long ago. If you have a mystery and are curious, you start looking for clues. Scientists are doing that right now. They may not figure it all out before you are a grown up. When you get older maybe you could help find clues to this mystery as well. What kinds of clues do you think would be helpful in learning about things that happened long ago?

Disciplinary Core Ideas

ESS1.C: The History of Planet Earth: Some events happen very quickly; others occur very slowly, over a time period much longer than one can observe. (2-ESS1-1)

ESS3.A: Natural Resources: Living things need water, air, and resources from the land, and they live in places that have the things they need. Humans use natural resources for everything they do. (K-ESS3-1)

Crosscutting Concepts

Patterns: Patterns in the natural and human designed world can be observed and used as evidence. (K-LS1-1)

Big Ideas: How life got started on Earth is a mystery. Scienists are piecing together the clues to learn more about how life began on Earth.

Boundaries: In this grade band, Earth events are described in terms of relative time rather than quantitative measurements of timescales. (2-ESS1-1)

No appropriate content for this grade level. Please use the navigation arrows to switch levels.

Grades 3-5 or Adult Emerging Learner

The Earth is really old. It’s older than any grownups you know, it’s older than human civilization, and it’s older than the time when the dinosaurs were alive. But, as old as Earth is, we’ve found evidence that tells us that living things have been around on Earth for almost as long as our planet has been here.

Life started on Earth so long ago that it’s hard for us to know exactly how it started. But there are scientists out there who are collecting information from old rocks, running experiments in laboratories, and using computer programs to test their ideas in order to learn more about the origin of life on Earth. It’s a pretty big mystery to try to uncover and we might never know for sure how life started, but we’re getting closer and closer to understanding how it could have happened.

ESS1.C: The History of Planet Earth: Local, regional, and global patterns of rock formations reveal changes over time due to Earth forces, such as earthquakes. The presence and location of certain fossil types indicate the order in which rock layers were formed. (4-ESS1-1)

LS2.B: Cycles of Matter and Energy Transfer in Ecosystems: Matter cycles between the air and soil and among plants, animals, and microbes as these organisms live and die. Organisms obtain gases, and water, from the environment, and release waste matter (gas, liquid, or solid) back into the environment. (5-LS2-1)

ESS2.E: Biogeology: Living things affect the physical characteristics of their regions. (4-ESS2-1)

Patterns: Patterns can be used as evidence to support an explanation. (4-ESS1-1, 4-ESS2-2)

Big Ideas: The Earth has been around for a very long time. Scientists are investigating the early Earth environment and possible ways life started on Earth. Certain features, like rocks, can be analyzed to order events that have occurred on Earth.

Boundaries: Examples of information obtained from old rocks include rock layers with marine shell fossils above rock layers with plant fossils and no shells, indicating a change from land to water over time; and, a canyon with different rock layers in the walls and a river in the bottom, indicating that over time a river cut through the rock. Emphasis is on relative time. (4-ESS1-1)

Grades 6-8 or Adult Building Learner

The Earth is really old. Using the tools of science, we have learned that Earth is about 4.5 billion years old. As old as Earth is, we’ve found evidence that tells us that living things have been around on Earth for almost as long as our planet has been here. We have evidence that tells us that life may have been on Earth as far back as about 4 billion years ago.

Life started on Earth so long ago that it’s hard for us to know exactly how it started. But there are scientists out there who are trying to figure that out. They include people who study the fossils of ancient bacteria or look for other signs of ancient life in old rocks. There are also people who are running experiments in laboratories to see how the basic building blocks of life can come together to make living things. And there are people who use computer programs to test our ideas about how life might have started.

Uncovering the origin of life on Earth is a pretty big mystery to try to solve. We might never actually know for sure how life started, but we’re getting closer and closer to understanding how it could have happened here on Earth and possibly on other worlds as well.

ESS1.C: The History of Planet Earth: The geologic time scale interpreted from rock strata provides a way to organize Earth’s history. Analyses of rock strata and the fossil record provide only relative dates, not an absolute scale. (MS-ESS1-4)

ESS2.A: Earth’s Materials and Systems: The planet’s systems interact over scales that range from microscopic to global in size, and they operate over fractions of a second to billions of years. These interactions have shaped Earth’s history and will determine its future. (MS-ESS2-2) All Earth processes are the result of energy flowing and matter cycling within and among the planet’s systems. This energy is derived from the Sun and Earth’s hot interior. The energy that flows and matter that cycles produce chemical and physical changes in Earth’s materials and living organisms. (MS-ESS2-1)

ESS2.B: Plate Tectonics and Large-Scale System Interactions: Maps of ancient land and water patterns, based on investigations of rocks and fossils, make clear how Earth’s plates have moved great distances, collided, and spread apart. (MS-ESS2-3)

Scale Proportion and Quantity: Time, space, and energy phenomena can be observed at various scales using models to study systems that are too large or too small. (MS-ESS1-4, MS-ESS2-2)

Big Ideas: The Earth has been around for a very long time. Scientists are investigating the early Earth environment and possible ways life started on Earth. Certain features, like rocks, can be used to order events that have occurred on Earth. There are still many aspects of early life that are unknown. Uncovering how life began on Earth can help with understanding how life could have possibly began on other worlds.

Boundaries: Emphasis is on how analyses of rock formations and the fossils they contain are used to establish relative ages of major events in Earth’s history. Examples of Earth’s major events could range from being very recent (such as the last Ice Age or the earliest fossils of homo sapiens) to very old (such as the formation of Earth or the earliest evidence of life). Examples can include the formation of mountain chains and ocean basins, the evolution or extinction of particular living organisms, or significant volcanic eruptions. Assessment does not include recalling the names of specific periods or epochs and events within them. (MS-ESS1-4)

6-12 Astrobiology Math. This collection of math problems provides an authentic glimpse of modern astrobiology science and engineering issues, often involving actual research data. Students explore concepts in astrobiology through calculations. Relevant topics include The Origin of Life (page 3) and Miller-Urey Experiment: Complex Organic Molecules (page 13) where students explore concepts in science through calculations. NASA . https://www.nasa.gov/pdf/637832main_Astrobiology_Math.pdf

Grades 9-12 or Adult Sophisticated Learner

One of the greatest mysteries about life on our planet is when and how it first started. Life appears to have been here for a very long time. Using the tools of science, we have learned that Earth is about 4.5 billion years old. And, as old as Earth is, we’ve found evidence that tells us that living things have been around on Earth for almost as long as our planet has been here. We have evidence that tells us that life may have been on Earth as far back as about 4 billion years ago and maybe even before that.

Life started on Earth so long ago that it’s hard for us to know exactly how it started. But there are scientists out there who are trying to figure that out. They include field scientists who study the fossils of ancient bacteria or look for other signs of ancient life in old rocks. For instance, they sometimes will look at the isotopes of elements like carbon that are trapped in old rocks to see if they imply biological activity. If they find such evidence, they can then also use other information from the rocks to figure out what kind of environment was available for the potential living things that were around when the rock formed. There are also scientists who are running experiments in laboratories to see how the basic building blocks of life can come together to make living things. For example, some lab experiments can be set up to figure out what conditions would be necessary for cell membranes to form without life. It turns out that some molecules can come together to make pockets just like cells under the right conditions. Outside of studying clues that we can find in the rocks and running experiments in labs, we can also use computer programs to test our ideas about how life might have started. All of these kinds of research projects have helped us to learn a lot more about how life might have come about on our planet.

Many scientists agree that the earliest life would have needed a good bit of water, the fundamental CHNOPS elements present to make organic molecules, and some way to concentrate simple organic molecules (since that would be necessary to make more complex molecules for biological processes). This can happen in tidal zones around the ocean, in little droplets of water that get sprayed into the atmosphere from ocean waves, where hydrothermal vents form on the ocean floor, or maybe even in small ponds or lakes when they dry up. It would also have been necessary to bring these molecules together in just the right way to make some chemical reactions more likely to occur. It turns out that some minerals, including pyrite (made of iron and sulfur) and many clays, are really good at orienting molecules in ways that causes them to react with each other. Life as we know it is based on cells, so an environment where life emerges would also need naturally-made containers with an inside and outside. It turns out that little enclosures with lipid membranes, just like cells, can form without life (also called “abiotically”). Depending on the chemistry of the fluid involved, these non-living cells can form automatically.

Environmental niches being investigated as potential places for the origin of life on Earth include surface waters such as lakes and ponds, sea ice, hydrothermal vents, tide pools, and hot springs. All of these areas currently have living things thriving in them, many of which are considered to be extremophiles. Investigations on the genetics of known organisms on Earth has suggested that the earliest life might have been thermophilic (adapted to hotter environments), which has caused a lot of people to suspect that hydrothermal systems might be important for the formation of life. As we learn more about how life on Earth may have started, it helps us to better understand the places we should first look at on other worlds in our solar system and beyond if we want to see if alien life exists. For instance, the possibility for hydrothermal vents to be active and possible sites of living processes in the oceans of Europa and Enceladus make these two moons really important places for us to study.

Uncovering the origin of life on Earth is a pretty big mystery to try to solve. We might never actually know for sure how life started, but we’re getting closer and closer to understanding how it could have happened here on Earth and possibly on other worlds as well. Perhaps the emergence of life on a world isn’t just something that happens on it, but rather to it. Some people suspect that the development of life is a natural process that occurs for many worlds in the Universe, but we can’t test that idea or figure out how common life may be until we’ve first discovered whether or not we’re alone.

ESS1.C: The History of Planet Earth: Continental rocks, which can be older than 4 billion years, are generally much older than the rocks of the ocean floor, which are less than 200 million years old. (HS-ESS1-5) *Although active geologic processes, such as plate tectonics and erosion, have destroyed or altered most of the very early rock record on Earth, other objects in the solar system, such as lunar rocks, asteroids, and meteorites, have changed little over billions of years. Studying these objects can provide information about Earth’s formation and early history. (HS-ESS1-6)

ESS2.A: Earth Materials and Systems: Earth’s systems, being dynamic and interacting, cause feedback effects that can increase or decrease the original changes. (HS-ESS2-1)

ESS2.C: The Roles of Water in Earth’s Surface Processes: The abundance of liquid water on Earth’s surface and its unique combination of physical and chemical properties are central to the planet’s dynamics. These properties include water’s exceptional capacity to absorb, store, and release large amounts of energy, transmit sunlight, expand upon freezing, dissolve and transport materials, and lower the viscosities and melting points of rocks. (HS-ESS2-5)

ESS2.E: Biogeology: The many dynamic and delicate feedbacks between the biosphere and other Earth systems cause a continual co-evolution of Earth’s surface and the life that exists on it. (HS-ESS2-7)

PS1.B: Chemical Reactions: Chemical processes, their rates, and whether or not energy is stored or released can be understood in terms of the collisions of molecules and the rearrangements of atoms into new molecules, with consequent changes in the sum of all bond energies in the set of molecules that are matched by changes in kinetic energy. (HS-PS1-4, HS-PS1-5) *In many situations, a dynamic and condition-dependent balance between a reaction and the reverse reaction determines the numbers of all types of molecules present. (HS-PS1-6)

PS3.A: Definitions of Energy: Energy is a quantitative property of a system that depends on the motion and interactions of matter and radiation within that system. That there is a single quantity called energy is due to the fact that a system’s total energy is conserved, even as, within the system, energy is continually transferred from one object to another and between its various possible forms. (HS-PS3-1, HS-PS3-2)

LS1.A: Structure and Function: Systems of specialized cells within organisms help them perform the essential functions of life. (HS-LS1-1) *All cells contain genetic information in the form of DNA molecules. Genes are regions in the DNA that contain the instructions that code for the formation of proteins, which carry out most of the work of cells. (HS-LS1-1)

Systems and System Models: Models (e.g., physical, mathematical, computer models) can be used to simulate systems and interactions — including energy, matter, and information flows — within and between systems at different scales. (HS-LS1-2)

Big Ideas: The Earth has been around for about 4.5 billion years. Evidence indicates living things have been on Earth for about 4 billion years. Scientists are investigating the early Earth environment and possible ways life started on Earth. Certain features, like rocks, can be used to order events that have occurred on Earth. Environmental niches with rather extreme conditions are being studied as locations for early Earth life. There are still many aspects of early life that are unknown. Uncovering how life began on Earth can help with understanding how life could have possibly began on other worlds.

Boundaries: In this grade band, emphasis is placed on using available evidence within the solar system to reconstruct the early history of Earth, which formed along with the rest of the solar system 4.6 billion years ago. Examples of evidence include the absolute ages of ancient materials (obtained by radiometric dating of meteorites, moon rocks, and Earth’s oldest minerals), the sizes and compositions of solar system objects, and the impact cratering record of planetary surfaces. (HS-ESS1-6)

9-10 Voyages through Time: Origin of Life. Through the Origin of Life module students address questions such as: What is life? What is the evidence for early evolution of life on Earth? How did life begin? Sample lesson on the website and the curriculum is available for purchase. SETI . http://www.voyagesthroughtime.org/origin/index.html

10-12 Is Anyone Out There? In this 20-minute TED talk, John Delano speaks to the early Earth the beginning of life on Earth as a mystery that illuminates the possibilities for life to be found beyond Earth. He outlines the evidence and continued areas of study for four main questions: Where did the prebiotic molecules come from? How were they assembled into complex molecules? When did life originate? and What does life remember about the old days (implying evidence for the circumstances of the origin of life)? John Delano/TED. https://www.youtube.com/watch?v=qrQY7vQy50M

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The Scientific Consensus on When a Human's Life Begins

Affiliation.

• 1 J.D., Northwestern University School of Law, 2016; Ph.D., The University of Chicago, 2019.
• PMID: 36629778

Peer-reviewed journals in the biological and life sciences literature have published articles that represent the biological view that a human's life begins at fertilization ("the fertilization view"). As those statements are typically offered without explanation or citation, the fertilization view seems to be uncontested by the editors, reviewers, and authors who contribute to scientific journals. However, Americans are split on whether the fertilization view is a "philosophical or religious belief" (45%) or a "biological and scientific fact" (46%), and only 38% of Americans view fertilization as the starting point of a human's life. In the two studies that explored experts' views on the matter, the fertilization view was the most popular perspective held by public health and IVF professionals. Since a recent study suggested that 80% of Americans view biologists as the group most qualified to determine when a human's life begins, experts in biology were surveyed to provide a new perspective to the literature on experts' views on this matter. Biologists from 1,058 academic institutions around the world assessed survey items on when a human's life begins and, overall, 96% (5337 out of 5577) affirmed the fertilization view. The founding principles of the field Science Communication suggest that scientists have an ethical and professional obligation to inform Americans, as well as people around the world, about scientific developments so members of the public can be empowered to make life decisions that are consistent with the best information available. Given that perspective-and a recent study's finding that a majority of Americans believe they deserve to know when a human's life begins in order to make informed reproductive decisions-science communicators should work to increase the level of science awareness on the fertilization view, as it stands alone as the leading biological perspective on when a human's life begins.

Keywords: abortion; fertilization; human rights; personhood; science communication; scientific consensus; when a human’s life begins; when life begins.

Copyright © 2021 by the National Legal Center for the Medically Dependent and Disabled, Inc.

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how life began 1 Pages 297 Words

             About 4.6 billion years ago the Earth was a fiery mass of liquid matter. As the hot mass began to cool, a rock crust formed on the Earth's surface, and the gases escaping from the newly made rocks formed the early atmosphere. The early atmosphere was made up of methane, ammonia, water vapor and hydrogen. There was no free oxygen in the early atmosphere. As the Earth cooled further the water vapor condensed, flooding the Earth with rain to form the oceans.              Life begun in the harsh environments that dominated the early Earth, such as hot springs, submarine volcanic vents or in hot rocks deep within the Earth. Early forms of bacteria began to evolve about 3500-3800 million years ago, when there was little oxygen in the atmosphere. They produced energy using sources other than oxygen, such as nitrogen and sulfur compounds. Species similar to these early bacteria survive today and are found only in harsh environments, such as hot springs or deep in the Earth, where there is no oxygen. Oxygen is poisonous to these species. Some of the early bacteria evolved in a way to use the sun's energy to create a chemical reaction called photosynthesis.              The earliest living things on Earth were primitive forms of bacteria. They were single-celled organisms with their genetic material free in their cells, not inside a nucleus. These types of cells are known as prokaryotes.              About 1800 million years ago, new, complex, single-celled organisms evolved. They were called eucaryotes and had their DNA inside a nucleus, like the cells of most organisms today. Eucaryotes also had organelles inside the cell that performed a number of important functions. Some organelles are derived from free-living bacteria that became incorporated into, and formed beneficial relationships with, these early eucaryotes.              ...

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