Oceanic vent systems and other hydrothermal systems have a zonal structure reflected in ancient volcanogenic massive sulfide deposits VMS of hydrothermal origin. They reach many kilometres in diameter and date back to the Archean Eon. ZnS and MnS have a unique ability to store radiation energy, e. The Zn-world theory has been further filled out with experimental and theoretical evidence for the ionic constitution of the interior of the first proto-cells before archaea, bacteria and proto-eukaryotes evolved. Archibald Macallum noted the resemblance of body fluids such as blood and lymph to seawater;  however, the inorganic composition of all cells differ from that of modern seawater, which led Mulkidjanian and colleagues to reconstruct the "hatcheries" of the first cells combining geochemical analysis with phylogenomic scrutiny of the inorganic ion requirements of universal components of modern cells.
Geochemical reconstruction shows that the ionic composition conducive to the origin of cells could not have existed in what we today call marine settings but is compatible with emissions of vapour-dominated zones of what we today call inland geothermal systems. Under the oxygen depleted, CO 2 -dominated primordial atmosphere, the chemistry of water condensates and exhalations near geothermal fields would resemble the internal milieu of modern cells.
The deep sea vent, or alkaline hydrothermal vent , theory posits that life may have begun at submarine hydrothermal vents,   William Martin and Michael Russell have suggested "that life evolved in structured iron monosulphide precipitates in a seepage site hydrothermal mound at a redox, pH, and temperature gradient between sulphide-rich hydrothermal fluid and iron II -containing waters of the Hadean ocean floor.
The naturally arising, three-dimensional compartmentation observed within fossilized seepage-site metal sulphide precipitates indicates that these inorganic compartments were the precursors of cell walls and membranes found in free-living prokaryotes. The known capability of FeS and NiS to catalyze the synthesis of the acetyl-methylsulphide from carbon monoxide and methylsulphide, constituents of hydrothermal fluid, indicates that pre-biotic syntheses occurred at the inner surfaces of these metal-sulphide-walled compartments, The vents form a sustained chemical energy source derived from redox reactions, in which electron donors molecular hydrogen react with electron acceptors carbon dioxide ; see Iron—sulfur world theory.
These are highly exothermic reactions. Michael Russell demonstrated that alkaline vents created an abiogenic proton motive force PMF chemiosmotic gradient,  in which conditions are ideal for an abiogenic hatchery for life. These two gradients taken together can be expressed as an electrochemical gradient , providing energy for abiogenic synthesis.
The proton motive force can be described as the measure of the potential energy stored as a combination of proton and voltage gradients across a membrane differences in proton concentration and electrical potential. Szostak suggested that geothermal activity provides greater opportunities for the origination of life in open lakes where there is a buildup of minerals. In , based on spectral analysis of sea and hot mineral water, Ignat Ignatov and Oleg Mosin demonstrated that life may have predominantly originated in hot mineral water.
The hot mineral water that contains bicarbonate and calcium ions has the most optimal range. This water has a pH of 9—11 and is possible to have the reactions in seawater. According to Melvin Calvin , certain reactions of condensation-dehydration of amino acids and nucleotides in individual blocks of peptides and nucleic acids can take place in the primary hydrosphere with pH at a later evolutionary stage.
This is the environment in which the stromatolites have been created. Stromatolites survive in hot mineral water and in proximity to areas with volcanic activity. In , Tadashi Sugawara from the University of Tokyo created a protocell in hot water. Experimental research and computer modelling suggest that the surfaces of mineral particles inside hydrothermal vents have catalytic properties similar to those of enzymes and are able to create simple organic molecules, such as methanol CH 3 OH and formic , acetic and pyruvic acid out of the dissolved CO 2 in the water.
The research reported above by William F. Today's bioenergetic process of fermentation is carried out by either the aforementioned citric acid cycle or the Acetyl-CoA pathway, both of which have been connected to the primordial Iron—sulfur world. In a different approach, the thermosynthesis hypothesis considers the bioenergetic process of chemiosmosis , which plays an essential role in cellular respiration and photosynthesis, more basal than fermentation: First, life needed an energy source to bring about the condensation reaction that yielded the peptide bonds of proteins and the phosphodiester bonds of RNA.
In a generalization and thermal variation of the binding change mechanism of today's ATP synthase, the "first protein" would have bound substrates peptides, phosphate, nucleosides, RNA 'monomers' and condensed them to a reaction product that remained bound until after a temperature change it was released by thermal unfolding. The energy source under the thermosynthesis hypothesis was thermal cycling, the result of suspension of protocells in a convection current, as is plausible in a volcanic hot spring; the convection accounts for the self-organization and dissipative structure required in any origin of life model.
The still ubiquitous role of thermal cycling in germination and cell division is considered a relic of primordial thermosynthesis. By phosphorylating cell membrane lipids, this "first protein" gave a selective advantage to the lipid protocell that contained the protein. This protein also synthesized a library of many proteins, of which only a minute fraction had thermosynthesis capabilities. As proposed by Dyson,  it propagated functionally: Functioning daughters consisted of different amino acid sequences.
Whereas the Iron—sulfur world identifies a circular pathway as the most simple, the thermosynthesis hypothesis does not even invoke a pathway: ATP synthase's binding change mechanism resembles a physical adsorption process that yields free energy,  rather than a regular enzyme's mechanism, which decreases the free energy. It has been claimed that the emergence of cyclic systems of protein catalysts is implausible.
Montmorillonite , an abundant clay , is a catalyst for the polymerization of RNA and for the formation of membranes from lipids. Ferris' studies have also confirmed that clay minerals of montmorillonite catalyze the formation of RNA in aqueous solution, by joining nucleotides to form longer chains. In , Bart Kahr from the University of Washington and colleagues reported their experiments that tested the idea that crystals can act as a source of transferable information, using crystals of potassium hydrogen phthalate.
They then examined the distribution of imperfections in the new crystals and found that the imperfections in the mother crystals were reproduced in the daughters, but the daughter crystals also had many additional imperfections. For gene-like behaviour to be observed, the quantity of inheritance of these imperfections should have exceeded that of the mutations in the successive generations, but it did not.
Thus Kahr concluded that the crystals "were not faithful enough to store and transfer information from one generation to the next. In the s, Thomas Gold proposed the theory that life first developed not on the surface of the Earth, but several kilometres below the surface. It is claimed that discovery of microbial life below the surface of another body in our Solar System would lend significant credence to this theory.
Thomas Gold also asserted that a trickle of food from a deep, unreachable, source is needed for survival because life arising in a puddle of organic material is likely to consume all of its food and become extinct. Gold's theory is that the flow of such food is due to out-gassing of primordial methane from the Earth's mantle; more conventional explanations of the food supply of deep microbes away from sedimentary carbon compounds is that the organisms subsist on hydrogen released by an interaction between water and reduced iron compounds in rocks.
Panspermia is the hypothesis that life exists throughout the universe , distributed by meteoroids , asteroids , comets ,  planetoids ,  and, also, by spacecraft in the form of unintended contamination by microorganisms. The panspermia hypothesis does not attempt to explain how life first originated, but merely shifts it to another planet or a comet.
List of microorganisms tested in outer space. An organic compound is any member of a large class of gaseous, liquid, or solid chemicals whose molecules contain carbon. Carbon is the fourth most abundant element in the Universe by mass after hydrogen, helium , and oxygen. Observations suggest that the majority of organic compounds introduced on Earth by interstellar dust particles are considered principal agents in the formation of complex molecules, thanks to their peculiar surface-catalytic activities.
Glycolaldehyde, the first example of an interstellar sugar molecule, was detected in the star-forming region near the centre of our galaxy. These findings suggest that complex organic molecules may form in stellar systems prior to the formation of planets, eventually arriving on young planets early in their formation. NASA announced in that scientists had identified another fundamental chemical building block of life in a comet for the first time, glycine, an amino acid, which was detected in material ejected from comet Wild 2 in and grabbed by NASA's Stardust probe.
Glycine has been detected in meteorites before. Carl Pilcher, who leads the NASA Astrobiology Institute commented that "The discovery of glycine in a comet supports the idea that the fundamental building blocks of life are prevalent in space, and strengthens the argument that life in the universe may be common rather than rare. It is possible that a rain of material from comets could have brought significant quantities of such complex organic molecules to Earth. Polycyclic aromatic hydrocarbons PAH are the most common and abundant of the known polyatomic molecules in the observable universe , and are considered a likely constituent of the primordial sea.
Pyrimidine, like PAHs, the most carbon-rich chemical found in the Universe, may have been formed in red giant stars or in interstellar dust and gas clouds. The lipid world theory postulates that the first self-replicating object was lipid-like. These molecules were not present on early Earth, but other amphiphilic long-chain molecules also form membranes.
Furthermore, these bodies may expand by insertion of additional lipids , and under excessive expansion may undergo spontaneous splitting which preserves the same size and composition of lipids in the two progenies. The main idea in this theory is that the molecular composition of the lipid bodies is the preliminary way for information storage, and evolution led to the appearance of polymer entities such as RNA or DNA that may store information favourably.
Studies on vesicles from potentially prebiotic amphiphiles have so far been limited to systems containing one or two types of amphiphiles. This in contrast to the output of simulated prebiotic chemical reactions, which typically produce very heterogeneous mixtures of compounds. Among all these potential combinations, a specific local arrangement of the membrane would have favoured the constitution of a hypercycle,   actually a positive feedback composed of two mutual catalysts represented by a membrane site and a specific compound trapped in the vesicle.
A problem in most scenarios of abiogenesis is that the thermodynamic equilibrium of amino acid versus peptides is in the direction of separate amino acids. What has been missing is some force that drives polymerization. The resolution of this problem may well be in the properties of polyphosphates. Several mechanisms of organic molecule synthesis have been investigated. Polyphosphates cause polymerization of amino acids into peptides. They are also logical precursors in the synthesis of such key biochemical compounds as adenosine triphosphate ATP.
A key issue seems to be that calcium reacts with soluble phosphate to form insoluble calcium phosphate apatite , so some plausible mechanism must be found to keep calcium ions from causing precipitation of phosphate. There has been much work on this topic over the years, but an interesting new idea is that meteorites may have introduced reactive phosphorus species on the early Earth.
Polycyclic aromatic hydrocarbons PAH are known to be abundant in the universe,    including in the interstellar medium , in comets, and in meteorites, and are some of the most complex molecules so far found in space. Other sources of complex molecules have been postulated, including extraterrestrial stellar or interstellar origin. For example, from spectral analyses, organic molecules are known to be present in comets and meteorites.
In , a team detected traces of PAHs in a nebula. In the disk of material surrounding the star, there is a very large range of molecules, including cyanide compounds, hydrocarbons , and carbon monoxide. In September , NASA scientists reported that PAHs, subjected to interstellar medium conditions, are transformed, through hydrogenation , oxygenation and hydroxylation , to more complex organics—"a step along the path toward amino acids and nucleotides, the raw materials of proteins and DNA, respectively.
PAHs seem to have been formed shortly after the Big Bang, are widespread throughout the universe,    and are associated with new stars and exoplanets. Zachary Adam claims that tidal processes that occurred during a time when the Moon was much closer may have concentrated grains of uranium and other radioactive elements at the high-water mark on primordial beaches, where they may have been responsible for generating life's building blocks. Such radioactive beach sand might have provided sufficient energy to generate organic molecules, such as amino acids and sugars from acetonitrile in water.
Radioactive monazite material also has released soluble phosphate into the regions between sand-grains, making it biologically "accessible. Radioactive actinides , left behind in some concentration by the reaction, might have formed part of organometallic complexes. These complexes could have been important early catalysts to living processes. John Parnell has suggested that such a process could provide part of the "crucible of life" in the early stages of any early wet rocky planet, so long as the planet is large enough to have generated a system of plate tectonics which brings radioactive minerals to the surface.
As the early Earth is thought to have had many smaller plates, it might have provided a suitable environment for such processes. The 19th-century Austrian physicist Ludwig Boltzmann first recognized that the struggle for existence of living organisms was neither over raw material nor energy , but instead had to do with entropy production derived from the conversion of the solar spectrum into heat by these systems.
This formalism became known as Classical Irreversible Thermodynamics and Prigogine was awarded the Nobel Prize in Chemistry in "for his contributions to non-equilibrium thermodynamics , particularly the theory of dissipative structures ". Non-equilibrium thermodynamics has since been successfully applied to the analysis of living systems, from the biochemical production of ATP  to optimizing bacterial metabolic pathways  to complete ecosystems.
This theory postulates that the hallmark of the origin and evolution of life is the microscopic dissipative structuring of organic pigments and their proliferation over the entire Earth surface. This heat then catalyzes a host of secondary dissipative processes such as the water cycle , ocean and wind currents, hurricanes , etc. Michaelian has shown using the formalism of non-linear irreversible thermodynamics that there would have existed during the Archean a thermodynamic imperative to the abiogenic UV-C photochemical synthesis and proliferation of these pigments over the entire Earth surface if they acted as catalysts to augment the dissipation of the solar photons.
It has been suggested, however, that such changes in the surface flux of ultraviolet radiation due to geophysical events affecting the atmosphere could have been what promoted the development of complexity in life based on existing metabolic pathways, for example during the Cambrian explosion . Many salient characteristics of the fundamental molecules of life those found in all three domains all point directly to the involvement of UV-C light in the dissipative structuring of incipient life.
Michaelian suggests that it is erroneous to expect to describe the emergence, proliferation, or even evolution, of life without overwhelming reference to entropy production through the dissipation of a generalized chemical potential, in particular, the prevailing solar photon flux. Different forms of life with variable origin processes may have appeared quasi-simultaneously in the early history of Earth.
It has been proposed that:. The first organisms were self-replicating iron-rich clays which fixed carbon dioxide into oxalic and other dicarboxylic acids. This system of replicating clays and their metabolic phenotype then evolved into the sulfide rich region of the hotspring acquiring the ability to fix nitrogen. Finally phosphate was incorporated into the evolving system which allowed the synthesis of nucleotides and phospholipids.
If biosynthesis recapitulates biopoiesis, then the synthesis of amino acids preceded the synthesis of the purine and pyrimidine bases. Furthermore the polymerization of the amino acid thioesters into polypeptides preceded the directed polymerization of amino acid esters by polynucleotides.
The only known environments that mimic the needed conditions on Earth are found in terrestrial hydrothermal pools fed by steam vents. Their hypothesized pre-biotic environments are similar to the deep-oceanic vent environments most commonly hypothesized, but add additional components that help explain peculiarities found in reconstructions of the Last Universal Common Ancestor LUCA of all living organisms.
Bruce Damer and David Deamer have come to the conclusion that cell membranes cannot be formed in salty seawater , and must therefore have originated in freshwater. Before the continents formed, the only dry land on Earth would be volcanic islands, where rainwater would form ponds where lipids could form the first stages towards cell membranes. These predecessors of true cells are assumed to have behaved more like a superorganism rather than individual structures, where the porous membranes would house molecules which would leak out and enter other protocells. Only when true cells had evolved would they gradually adapt to saltier environments and enter the ocean.
A theory that speaks to the origin of life on Earth and other rocky planets posits life as an information system in which information content grows because of selection. Life must start with minimum possible information, or minimum possible departure from thermodynamic equilibrium, and it requires thermodynamically free energy accessible by means of its information content. The most benign circumstances, minimum entropy variations with abundant free energy, suggest the pore space in the first few kilometres of the surface. Free energy is derived from the condensed products of the chemical reactions taking place in the cooling nebula.
From Wikipedia, the free encyclopedia. For non-scientific views on the origins of life, see Creation myth. For the oldest life forms, see Earliest known life forms. Timeline of the evolutionary history of life. Human timeline and Nature timeline. Earliest known life forms. For branching of Bacteria phyla, see Bacterial phyla. Human timeline and Life timeline. Serpentine is stable at high pH in the presence of brucite like calcium silicate hydrate, C-S-H phases formed along with portlandite Ca OH 2 in hardened Portland cement paste after the hydration of belite Ca 2 SiO 4 , the artificial calcium equivalent of forsterite.
Analogy of reaction 3 with belite hydration in ordinary Portland cement: Archived from the original on 8 September Retrieved 2 March The New York Times. Archived from the original on 2 March The Origin of Life. Translated by Morgulis, Sergius 2 ed. Spanish Society for Microbiology. Archived from the original PDF on 24 August Ever since the historical contributions by Aleksandr I. Oparin, in the s, the intellectual challenge of the origin of life enigma has unfolded based on the assumption that life originated on Earth through physicochemical processes that can be supposed, comprehended, and simulated; that is, there were neither miracles nor spontaneous generations.
Scharf, Caleb; et al. Retrieved 28 November What do we mean by the origins of life OoL? The term has largely replaced earlier concepts such as abiogenesis Kamminga, ; Fry, Georg von Holtzbrinck Publishing Group. According to the conventional hypothesis, the earliest living cells emerged as a result of chemical evolution on our planet billions of years ago in a process called abiogenesis. Retrieved 14 February Thomas Huxley — used the term abiogenesis in an important text published in He strictly made the difference between spontaneous generation, which he did not accept, and the possibility of the evolution of matter from inert to living, without any influence of life.
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- Xian, Beijing und kein! Chop Suey: Lehmsoldaten, Fuhunde und Genüsse in China (German Edition).
- Red Sails in the Fallout: A Dungeons & Dragons Novel (Dungeons & Dragons; Gamma World).
- Breach of Sanity!
- How life began..
Archived PDF from the original on 22 December Archived from the original on 13 October Retrieved 13 October Newly discovered diffuse interstellar bands". Archived from the original on 11 July Post is reprinted from materials provided by the Rochester Institute of Technology. Salt Lake City, UT: View image of Thomas Cech in Credit: Lockard, CC by 3. Thomas Cech was born and raised in Iowa.
As a child he was fascinated by rocks and minerals. By the time he was in junior high school he was visiting the local university and knocking on geologists' doors , asking to see models of mineral structures. In the early s, Cech and his colleagues at the University of Colorado Boulder were studying a single-celled organism called Tetrahymena thermophila. Part of its cellular machinery includes strands of RNA. Cech found that one particular section of the RNA sometimes detached from the rest, as if something had cut it out with scissors.
When the team removed all the enzymes and other molecules that might be acting as molecular scissors, the RNA kept doing it. They had discovered the first RNA enzyme: Cech published the results in The following year, another group found a second RNA enzyme — or "ribozyme", as it was dubbed. Finding two RNA enzymes in quick succession suggested that there were plenty more out there. Now the notion that life began with RNA was looking promising. A physicist who had become fascinated by molecular biology, Gilbert would also be one of the early advocates of sequencing the human genome.
The first stage of evolution, Gilbert argued, consisted of "RNA molecules performing the catalytic activities necessary to assemble themselves from a nucleotide soup". Eventually they found a way to make proteins and protein enzymes, which proved so useful that they largely supplanted the RNA versions and gave rise to life as we recognise it today.
The RNA World is an elegant way to make complex life from scratch. Instead of having to rely on the simultaneous formation of dozens of biological molecules from the primordial soup, one Jack-of-all-trades molecule could do the work of all of them. View image of The ribosome makes proteins Credit: Thomas Steitz had spent 30 years studying the structures of the molecules in living cells.
In the s he took on his biggest challenge: Every living cell has a ribosome. This huge molecule reads instructions from RNA and strings together amino acids to make proteins. The ribosomes in your cells built most of your body. The ribosome was known to contain RNA. But in Steitz's team produced a detailed image of the ribosome's structure , which showed that the RNA was the catalytic core of the ribosome. This was critical, because the ribosome is so fundamental to life, and so ancient.
But since then, doubts have crept back in. Right from the start, there were two problems with the RNA World idea. Could RNA really perform all the functions of life by itself? And could it have formed on the early Earth? It is 30 years since Gilbert set out the stall for the RNA World, and we still do not have hard evidence that RNA can do all the things the theory demands of it.
It is a handy little molecule, but it may not be handy enough. One task stood out. But no known RNA can self-replicate. So in the late s, a few biologists started a rather quixotic quest. They set out to make a self-replicating RNA for themselves. View image of Jack Szostak Credit: Jack Szostak of the Harvard Medical School was one of the first to get involved.
As a child he was so fascinated with chemistry that he had a lab in his basement. With a splendid disregard for his own safety, he once set off an explosion that embedded a glass tube into the ceiling. In the early s, Szostak helped to show how our genes protect themselves against the ageing process. This early research would eventually net him a share of a Nobel Prize. But he soon became fascinated by Cech's RNA enzymes. Szostak set out to improve on the discovery by evolving new RNA enzymes in the lab.
His team created a pool of random sequences and tested them to see which ones showed catalytic activity. They then took those sequences, tweaked them, and tested again. After 10 rounds of this, Szostak had produced an RNA enzyme that made a reaction go seven million times faster than it naturally would. They had showed that RNA enzymes could be truly powerful.
How Did Life Begin?
But their enzyme could not copy itself, not even close. Szostak had hit a wall. View image of RNA may not be up to the job of starting life Credit: The next big advance came in from Szostak's former student David Bartel , of the Massachusetts Institute of Technology in Cambridge. In other words, it was not just adding random nucleotides: This was still not a self-replicator, but it was edging towards it. R18 consisted of a string of nucleotides, and it could reliably add 11 nucleotides to a strand: The hope was that a few tweaks would allow it to make a strand nucleotides long — as long as itself.
His team created a modified R18 called tC19Z , which copies sequences up to 95 nucleotides long. In they created an RNA enzyme that replicates itself indirectly. Their enzyme joins together two short pieces of RNA to create a second enzyme. This then joins together another two RNA pieces to recreate the original enzyme. This simple cycle could be continued indefinitely, given the raw materials.
But the enzymes only worked if they were given the correct RNA strands, which Joyce and Lincoln had to make. View image of How could the molecules of life form somewhere like this? RNA does not seem to be up to the job of kick-starting life. The case has also been weakened by chemists' failure to make RNA from scratch. The problem is the sugar and the base that make up each nucleotide.
It is possible to make each of them individually, but the two stubbornly refuse to link together. This problem was already clear by the early s. It left many biologists with a nagging suspicion that the RNA World hypothesis, while neat, could not be quite right. Instead, maybe there was some other type of molecule on the early Earth: In , Peter Nielsen of the University of Copenhagen in Denmark came up with a candidate for the primordial replicator.
It was essentially a heavily-modified version of DNA. He called the new molecule polyamide nucleic acid , or PNA. Confusingly, it has since become known as peptide nucleic acid. PNA has never been found in nature. But it behaves a lot like DNA. A strand of PNA can even take the place of one of the strands in a DNA molecule, with the complementary bases pairing up as normal.
Stanley Miller was intrigued. In he produced some hard evidence. By then he was 70 years old, and had just suffered the first in a series of debilitating strokes that would ultimately leave him confined to a nursing home, but he was not quite done. He repeated his classic experiment, which we discussed in Chapter One, this time using methane, nitrogen, ammonia and water — and obtained the polyamide backbone of PNA.
This is basically DNA, but with a different sugar in its backbone. What's more, TNA can fold up into complex shapes , and even bind to a protein.
Similarly, in Eric Meggers made glycol nucleic acid , which can form helical structures. Each of these alternative nucleic acids has its supporters: But there is no trace of them in nature, so if the first life did use them, at some point it must have utterly abandoned them in favour of RNA and DNA.
This might be true, but there is no evidence. On the one hand, RNA enzymes existed and they included one of the most important pieces of biological machinery, the ribosome. The alternative nucleic acids might solve the latter problem, but there was no evidence they ever existed in nature. That was less good.
Meanwhile, a rival theory had been steadily gathering steam since the s. Instead it began as a mechanism for harnessing energy. View image of Life needs energy to stay alive Credit: We saw in Chapter Two how scientists divided into three schools of thought about how life began. One group was convinced that life began with a molecule of RNA, but they struggled to work out how RNA or similar molecules could have formed spontaneously on the early Earth and then made copies of themselves.
Their efforts were exciting at first, but ultimately frustrating. However, even while this research was progressing, there were other origin-of-life researchers who felt sure that life began in a completely different way.
The RNA World theory relies on a simple idea: Many biologists would agree with this. From bacteria to blue whales, all living things strive to have offspring. However, many origin-of-life researchers do not believe reproduction is truly fundamental. Before an organism can reproduce, they say, it has to be self-sustaining. It must keep itself alive. After all, you cannot have kids if you die first. We keep ourselves alive by eating food, while green plants do it by extracting energy from sunlight.
You might not think that a person wolfing down a juicy steak looks much like a leafy oak tree, but when you get right down to it, both are taking in energy. This process is called metabolism. First, you must obtain energy; say, from energy-rich chemicals like sugars. Then you must use that energy to build useful things like cells.
This process of harnessing energy is so utterly essential, many researchers believe it must have been the first thing life ever did. View image of Volcanic water is hot and rich in chemicals Credit: What might these metabolism-only organisms have looked like? He was not a full-time scientist, but rather a patent lawyer with a background in chemistry.
They were not made of cells. All the other things that make up modern organisms — like DNA, cells and brains — came later. The water was rich in volcanic gases like ammonia, and held traces of minerals from the volcano's heart. Where the water flowed over the rocks, chemical reactions began to take place.
In particular, metals from the water helped simple organic compounds to fuse into larger ones. The turning point was the creation of the first metabolic cycle. This is a process in which one chemical is converted into a series of other chemicals, until eventually the original chemical is recreated.
In the process, the entire system takes in energy, which can be used to restart the cycle — and to start doing other things. All the other things that make up modern organisms — like DNA, cells and brains — came later, built on the back of these chemical cycles. These metabolic cycles do not sound much like life. Your cells are essentially microscopic chemical processing plants, constantly turning one chemical into another.
Metabolic cycles may not seem life-like, but they are fundamental to life. He outlined which minerals made for the best surfaces and which chemical cycles might take place. His ideas began to attract supporters. But it was all still theoretical. Fortunately, it had already been made — a decade earlier. View image of Vents in the Pacific Credit: The ridges, they knew, were volcanically active. Corliss found that the ridges were pockmarked with, essentially, hot springs. Hot, chemical-rich water was welling up from below the sea floor and pumping out through holes in the rocks.
Astonishingly, these "hydrothermal vents" were densely populated by strange animals. There were huge clams, limpets, mussels, and tubeworms. The water was also thick with bacteria. All these organisms lived on the energy from the hydrothermal vents. The discovery of hydrothermal vents made Corliss's name. It also got him thinking. In he proposed that similar vents existed on Earth four billion years ago, and that they were the site of the origin of life. He would spend much of the rest of his career working on this idea. View image of Hydrothermal vents support strange life Credit: Corliss proposed that hydrothermal vents could create cocktails of chemicals.
Each vent, he said, was a kind of primordial soup dispenser. As hot water flowed up through the rocks, the heat and pressure caused simple organic compounds to fuse into more complex ones like amino acids, nucleotides and sugars. Closer to the boundary with the ocean, where the water was not quite as hot, they began linking into chains — forming carbohydrates, proteins, and nucleotides like DNA.
Then, as the water approached the ocean and cooled still further, these molecules assembled into simple cells. It was neat, and caught people's attention. But Stanley Miller, whose seminal origin-of-life experiment we discussed in Chapter One, was not convinced.
7 Theories on the Origin of Life
Writing in , he argued the vents were too hot. While extreme heat would trigger the formation of chemicals like amino acids, Miller's experiments suggested that it would also destroy them. Key compounds like sugars "would survive… for seconds at most". What's more, these simple molecules would be unlikely to link up into chains, because the surrounding water would break the chains almost immediately.
View image of Geologist and origin-of-life researcher Michael Russell Credit: At this point the geologist Mike Russell stepped into the fray. He thought that the vent theory could be made to work after all. This inspiration would lead him to create one of the most widely-accepted theories of the origin of life. Russell had spent his early life variously making aspirin, scouting for valuable minerals and — in one remarkable incident in the s — coordinating the response to a possible volcanic eruption, despite having no training.
But his real interest was in how Earth's surface has changed over the eons. This geological perspective has shaped his ideas on the origin of life. In the s he found fossil evidence of a less extreme kind of hydrothermal vent, where the temperatures were below C. These milder temperatures, he argued, would allow the molecules of life to survive far longer than Miller had assumed they would. What's more, the fossil remains of these cooler vents held something strange.
A mineral called pyrite, which is made of iron and sulphur, had formed into tubes about 1mm across. In his lab, Russell found that the pyrite could also form spherical blobs.
He suggested that the first complex organic molecules formed inside these simple pyrite structures. View image of A lump of iron pyrite Credit: James Petts, CC by 2. He had even proposed that pyrite was involved. So Russell put two and two together. If Russell was correct, life began at the bottom of the sea — and metabolism appeared first. Russell set all this out in a paper published in , 40 years after Miller's classic experiment.
It did not get the same excited media coverage, but it was arguably more important. Just to make it even more impressive, Russell also offered an explanation for how the first organisms obtained their energy. In other words, he figured out how their metabolism could have worked. His idea relied on the work of one of modern science's forgotten geniuses. In the s, the biochemist Peter Mitchell fell ill and was forced to resign from the University of Edinburgh. Instead, he set up a private lab in a remote manor house in Cornwall.
Isolated from the scientific community, his work was partly funded by a herd of dairy cows. Many biochemists, including, initially, Leslie Orgel , whose work on RNA we discussed in Chapter Two, thought that his ideas were utterly ridiculous. Less than two decades later, Mitchell achieved the ultimate victory: He has never been a household name, but his ideas are in every biology textbook. Mitchell spent his career figuring out what organisms do with the energy they get from food.
In effect, he was asking how we all stay alive from moment to moment. He knew that all cells store their energy in the same molecule: The crucial bit is a chain of three phosphates, anchored to the adenosine. Adding the third phosphate takes a lot of energy, which is then locked up in the ATP. When a cell needs energy — say, if a muscle needs to contract — it breaks the third phosphate off an ATP.
This turns it into adenosine diphosphate ADP and releases the stored energy. Mitchell wanted to know how the cells made the ATP in the first place. How did they concentrate enough energy onto an ADP, so that the third phosphate would attach? Mitchell knew that the enzyme that makes ATP sits on a membrane. So he suggested that the cell was pumping charged particles called protons across the membrane, so that there were lots of protons on one side and hardly any on the other. The protons would then try to flow back across the membrane to balance out the number of protons on each side — but the only place they could get through was the enzyme.
The stream of protons passing through gave the enzyme the energy it needed to make ATP. Mitchell first set out this idea in He spent the next 15 years defending it from all comers , until the evidence became irrefutable. We now know that the process Mitchell identified is used by every living thing on Earth. It is happening inside your cells right now. Like DNA, it is fundamental to life as we know it. The key point that Russell picked up on is Mitchell's proton gradient: All cells need a proton gradient to store energy. Modern cells create the gradients by pumping protons across a membrane, but this involves complex molecular machinery that cannot have just popped into existence.
So Russell made one more logical leap: Somewhere like a hydrothermal vent. But it would have to be a specific type of vent. When Earth was young the seas were acidic, and acidic water has a lot of protons floating around inside it. To create a proton gradient, the water from the vent must have been low in protons: Corliss's vents would not do.
Not only were they too hot, they were acidic. But in , Deborah Kelley of the University of Washington discovered the first alkaline vents. Kelley had to battle just to become a scientist in the first place. Her father died as she was finishing high school, and she was forced to work long hours to support herself through college. But she succeeded, and became fascinated both by undersea volcanoes and the searing hot hydrothermal vents. Those twin loves eventually led her to the middle of the Atlantic Ocean.
There, Earth's crust is being pulled apart and a ridge of mountains rises from the sea floor. On this ridge, Kelley found a field of hydrothermal vents that she called "Lost City". They are not like the ones Corliss found. The water flowing from them is only C, and mildly alkaline. Carbonate minerals from this water have clumped into steep, white "chimneys" that rise from the sea bed like organ pipes.
Their appearance is eerie and ghost-like, but this is misleading: These alkaline vents were the perfect fit for Russell's ideas. He became convinced that vents like those of Lost City were where life began. But he had a problem. Being a geologist, he did not know enough about biological cells to make his theory truly convincing. View image of "Black smoker" hydrothermal vent Credit: So Russell teamed up with biologist William Martin , a pugnacious American who has spent most of his career in Germany.
In the pair set out an improved version of Russell's earlier ideas. It is arguably the most fleshed-out story of how life began. Thanks to Kelley, they now knew that the rocks of alkaline vents were porous: These little pockets, they suggested, acted as "cells". Each pocket contained essential chemicals, including minerals like pyrite. Combined with the natural proton gradient from the vent, they were the ideal place for metabolism to begin. Once life had harnessed the chemical energy of the vent water, Russell and Martin say, it started making molecules like RNA. Eventually it created its own membrane and became a true cell, and escaped from the porous rock into the open water.
View image of Cells escaping from hydrothermal vents Credit: It found powerful support in July , when Martin published a study reconstructing some of the features of the "last universal common ancestor" LUCA. This is the organism that lived billions of years ago and from which all existing life is descended. We will probably never find direct fossil evidence of LUCA, but we can still make an educated guess as to how it might have looked and behaved by looking at microorganisms that do survive today.
This is what Martin did. He examined the DNA of 1, modern microorganisms, and identified genes that almost all of them had. This is arguably evidence that these genes have been passed down, from generation to generation, ever since those 1, microbes shared a common ancestor — roughly at the time that LUCA was alive. The genes included some for harnessing a proton gradient, but not genes for generating one — exactly as Russell and Martin's theories would predict.
What's more, LUCA seems to have been adapted to the presence of chemicals like methane, which suggests it inhabited a volcanically-active environment — like a vent. Despite this, RNA World supporters say the vent theory has two problems. One could potentially be fixed: View image of Vents are home to strange organisms Credit: The first problem is that there is no experimental evidence for the processes Russell and Martin describe.
They have a step-by-step story, but none of the steps have been seen in a lab. He has built an " origin of life reactor ", which will simulate the conditions inside an alkaline vent. He hopes to observe metabolic cycles, and perhaps even molecules like RNA. But it is early days. The second problem is the vents' location in the deep sea.
As Miller pointed out in , long-chain molecules like RNA and proteins cannot form in water without enzymes to help them. For many researchers, this is a knock-down argument. There are several theories as to how the amino acids might have made the leap into the complex, self-replicating life we see today. Some scientists believe that metabolism , in other words - the ability to break down carbon dioxide in the presence of a catalyst into small organic molecules - was how the first life developed. These reactions might have evolved to become more complex, and then genetic molecules somehow formed and joined in later.
There are many different theories as to exactly what types of molecules and catalysts would have been involved. Other scientists believe that the first living organisms were genes. These genes were single molecules that had developed in such a way as to be able to catalyze their own replication.
This theory seems more likely, since even simple systems such as crystals, have been demonstrated to evolve with modifications that breed true. Some scientists have suggested that certain compositions of clay create the right environment for these reactions to propagate. RNA is a complex molecule found in all living things that seems to be able to catalyze its own reproduction.
Many scientists believe that simple RNA molecules developed and eventually became more complex and developed into the organisms we see today. The idea is that all life on Earth has a common ancestor, kind of like a great-great-great They search for traits that are common across all life forms and assume that any traits that are common to all life forms today must have been inherited from LUCA, who had them all as well.