In biology, abiogenesis (from a-‘not’ + Greek bios ‘life’ + genesis 'origin') or the origin of life is the natural process by which life has arisen from non-living matter, such as simple organic compounds. The prevailing scientific hypothesis is that the transition from non-living to living entities was not a single event, but an evolutionary process of increasing complexity that involved the formation of a habitable planet, the prebiotic synthesis of organic molecules, molecular self-replication, self-assembly, autocatalysis, and the emergence of cell membranes. Many proposals have been made for different stages of the process.
Stages in the origin of life range from the well-understood, such as the habitable Earth and the abiotic synthesis of simple molecules, to the largely unknown, like the derivation of the last universal common ancestor (LUCA) with its complex molecular functionalities.
The study of abiogenesis aims to determine how pre-life chemical reactions gave rise to life under conditions strikingly different from those on Earth today. It primarily uses tools from biology and chemistry, with more recent approaches attempting a synthesis of many sciences. Life functions through the specialized chemistry of carbon and water, and builds largely upon four key families of chemicals: lipids for cell membranes, carbohydrates such as sugars, amino acids for protein metabolism, and nucleic acids DNA and RNA for the mechanisms of heredity. Any successful theory of abiogenesis must explain the origins and interactions of these classes of molecules. Many approaches to abiogenesis investigate how self-replicating molecules, or their components, came into existence. Researchers generally think that current life descends from an RNA world, although other self-replicating molecules may have preceded RNA.
The classic 1952 Miller–Urey experiment demonstrated that most amino acids, the chemical constituents of proteins, can be synthesized from inorganic compounds under conditions intended to replicate those of the early Earth. External sources of energy may have triggered these reactions, including lightning, radiation, atmospheric entries of micro-meteorites and implosion of bubbles in sea and ocean waves. Other approaches ("metabolism-first" hypotheses) focus on understanding how catalysis in chemical systems on the early Earth might have provided the precursor molecules necessary for self-replication.
NASA's 2015 strategy for astrobiology aimed to solve the puzzle of the origin of life – how a fully-functioning living system could emerge from non-living components – through research on the prebiotic origin of life's chemicals, both in space and on planets, as well as the functioning of early biomolecules to catalyse reactions and support inheritance.
The challenge for abiogenesis (origin of life) researchers is to explain how such a complex and tightly-interlinked system could develop by evolutionary steps, as at first sight all its parts are necessary to enable it to function. For example, a cell, whether the LUCA or in a modern organism, copies its DNA with the DNA polymerase enzyme, which is in turn produced by translating the DNA polymerase gene in the DNA. Neither the enzyme nor the DNA can be produced without the other. The evolutionary process could have involved molecular self-replication, self-assembly such as of cell membranes, and autocatalysis.
The precursors to the development of a living cell like the LUCA are clear enough, if disputed in their details: a habitable world is formed with a supply of minerals and liquid water. Prebiotic synthesis creates a range of simple organic compounds, which are assembled into polymers such as proteins and RNA. The process after the LUCA, too, is readily understood: Darwinian evolution caused the development of a wide range of species with varied forms and biochemical capabilities. The derivation of living things such as the LUCA from simple components, however, is far from understood.
Although Earth remains the only place where life is known, the science of astrobiology seeks evidence of life on other planets. The 2015 NASA strategy on the origin of life aimed to solve the puzzle by identifying interactions, intermediary structures and functions, energy sources, and environmental factors that contributed to the diversity, selection, and replication of evolvable macromolecular systems, and mapping the chemical landscape of potential primordial informational polymers. The advent of polymers that could replicate, store genetic information, and exhibit properties subject to selection was, it suggested, most likely a critical step in the emergence of prebiotic chemical evolution. Those polymers derived, in turn, from simple organic compounds such as nucleobases, amino acids and sugars that could have been formed by reactions in the environment. A successful theory of the origin of life must explain how all these chemicals came into being.
Conceptual history until the 1960sEdit
The Miller–Urey experiment was a synthesis of small organic molecules in a mixture of simple gases in a thermal gradient created by heating (right) and cooling (left) the mixture at the same time, with electrical discharges.
One ancient view of the origin of life, from Aristotle until the 19th century, is of spontaneous generation. This theory held that "lower" animals were generated by decaying organic substances, and that life arose by chance. This was questioned from the 17th century, in works like Thomas Browne's Pseudodoxia Epidemica. In 1665, Robert Hooke published the first drawings of a microorganism. In 1676, Antonie van Leeuwenhoek drew and described microorganisms, probably protozoa and bacteria. Van Leeuwenhoek disagreed with spontaneous generation, and by the 1680s convinced himself, using experiments ranging from sealed and open meat incubation and the close study of insect reproduction, that the theory was incorrect. In 1668 Francesco Redi showed that no maggots appeared in meat when flies were prevented from laying eggs. By the middle of the 19th century, spontaneous generation was considered disproven.
Another ancient idea dating back to Anaxagoras in the 5th century BC is panspermia, the idea that life exists throughout the universe, distributed by meteoroids, asteroids, comets and planetoids. It does not attempt to explain how life originated in itself, but shifts the origin of life on Earth to another heavenly body. The advantage is that life is not required to have formed on each planet it occurs on, but rather in a more limited set of locations (potentially even a single location), and then spread about the galaxy to other star systems via cometary or meteorite impact.
"A warm little pond": primordial soupEdit
The idea that life originated from non-living matter in slow stages appeared in Herbert Spencer's 1864–1867 book Principles of Biology, and in William Turner Thiselton-Dyer's 1879 paper "On spontaneous generation and evolution". On 1 February 1871 Charles Darwin wrote about these publications to Joseph Hooker, and set out his own speculation, suggesting that the original spark of life may have begun in a "warm little pond, with all sorts of ammonia and phosphoric salts, light, heat, electricity, &c., present, that a proteine compound was chemically formed ready to undergo still more complex changes." Darwin went on to explain that "at the present day such matter would be instantly devoured or absorbed, which would not have been the case before living creatures were formed."
Alexander Oparin in 1924 and J. B. S. Haldane in 1929 proposed that the first molecules constituting the earliest cells slowly self-organized from a primordial soup. Haldane suggested that the Earth's prebiotic oceans consisted of a "hot dilute soup" in which organic compounds could have formed.J. D. Bernal showed that such mechanisms could form most of the necessary molecules for life from inorganic precursors. In 1967, he suggested three "stages": the origin of biological monomers; the origin of biological polymers; and the evolution from molecules to cells.
In 1952, Stanley Miller and Harold Urey carried out a chemical experiment to demonstrate how organic molecules could have formed spontaneously from inorganic precursors under prebiotic conditions like those posited by the Oparin-Haldane hypothesis. It used a highly reducing (lacking oxygen) mixture of gases—methane, ammonia, and hydrogen, as well as water vapor—to form simple organic monomers such as amino acids. Bernal said of the Miller–Urey experiment that "it is not enough to explain the formation of such molecules, what is necessary, is a physical-chemical explanation of the origins of these molecules that suggests the presence of suitable sources and sinks for free energy." However, current scientific consensus describes the primitive atmosphere as weakly reducing or neutral, diminishing the amount and variety of amino acids that could be produced. The addition of iron and carbonate minerals, present in early oceans, however produces a diverse array of amino acids. Later work has focused on two other potential reducing environments: outer space and deep-sea hydrothermal vents.
The Earth was formed 4.54 Gya. The Hadean Earth (from its formation until 4 Gya) was at first inhospitable to any living organisms. During its formation, the Earth lost a significant part of its initial mass, and consequentially lacked the gravity to hold molecular hydrogen and the bulk of the original inert gases. The atmosphere consisted largely of water vapor, nitrogen, and carbon dioxide, with smaller amounts of carbon monoxide, hydrogen, and sulfur compounds. The solution of carbon dioxide in water is thought to have made the seas slightly acidic, with a pH of about 5.5. The Hadean atmosphere has been characterized as a "gigantic, productive outdoor chemical laboratory," similar to volcanic gases today which still support some abiotic chemistry.
Oceans may have appeared as soon as 200 million years after the Earth formed, in a near-boiling (100 C) reducing environment, as the pH of 5.8 rose rapidly towards neutral. This scenario has found support from the dating of 4.404 Gya zircon crystals from metamorphosed quartzite of Mount Narryer in Western Australia. Despite the likely increased volcanism, the Earth may have been a water world between 4.4 and 4.3 Gya, with little if any continental crust, a turbulent atmosphere, and a hydrosphere subject to intense ultraviolet light from a T Tauri stage Sun, from cosmic radiation, and from continued asteroid and comet impacts.
The Late Heavy Bombardment hypothesis posits that the Hadean environment between 4.28 and 3.8 Gya was highly hazardous to life. Following the Nice model, changes in the orbits of the giant planets may have bombarded the Earth with asteroids and comets that pockmarked the Moon and inner planets. Frequent collisions would have made photosynthesis unviable. The periods between such devastating events give time windows for the possible origin of life in early environments. If the deep marine hydrothermal setting was the site for the origin of life, then abiogenesis could have happened as early as 4.0-4.2 Gya. If the site was at the surface of the Earth, abiogenesis could have occurred only between 3.7 and 4.0 Gya. However, new lunar surveys and samples have led scientists, including an architect of the Nice model, to deemphasize the significance of the Late Heavy Bombardment.
If life evolved in the ocean at depths of more than ten meters, it would have been shielded both from late impacts and the then high levels of ultraviolet radiation from the sun. Geothermically heated oceanic crust could have yielded far more organic compounds through deep hydrothermal vents than the Miller–Urey experiments indicated. The available energy is maximized at 100–150 °C, the temperatures at which hyperthermophilic bacteria and thermoacidophilicarchaea live. These modern organisms may be among the closest surviving relatives of the LUCA.
Earliest evidence of lifeEdit
Life existed on Earth more than 3.5 Gya, during the Eoarchean when sufficient crust had solidified following the molten Hadean. The earliest physical evidence of life so far found consists of microfossils in the Nuvvuagittuq Greenstone Belt of Northern Quebec, in banded iron formation rocks at least 3.77 and possibly 4.28 Gya. The micro-organisms lived within hydrothermal vent precipitates, soon after the 4.4 Gya formation of oceans during the Hadean. The microbes resembled modern hydrothermal vent bacteria, supporting the view that abiogenesis began in such an environment.
Biogenic graphite has been found in 3.7 Gya metasedimentary rocks from southwestern Greenland and in microbial mat fossils from 3.49 Gya Western Australian sandstone. Evidence of early life in rocks from Akilia Island, near the Isua supracrustal belt in southwestern Greenland, dating to 3.7 Gya, have shown biogenic carbon isotopes. In other parts of the Isua supracrustal belt, graphite inclusions trapped within garnet crystals are connected to the other elements of life: oxygen, nitrogen, and possibly phosphorus in the form of phosphate, providing further evidence for life 3.7 Gya. In the Pilbara region of Western Australia, compelling evidence of early life was found in pyrite-bearing sandstone in a fossilized beach, with rounded tubular cells that oxidized sulfur by photosynthesis in the absence of oxygen.Zircons from Western Australia imply that life existed on Earth at least 4.1 Gya.
The Pilbara region of Western Australia contains the Dresser Formation with rocks 3.48 Gya, including layered structures called stromatolites. Their modern counterparts are created by photosynthetic micro-organisms including cyanobacteria. These lie within undeformed hydrothermal-sedimentary strata; their texture indicates a biogenic origin. Parts of the Dresser formation preserve hot springs on land, but other regions seem to have been shallow seas.
All chemical elements except for hydrogen and helium derive from stellar nucleosynthesis. The basic chemical ingredients of life – the carbon-hydrogen molecule (CH), the carbon-hydrogen positive ion (CH+) and the carbon ion (C+) – were produced by ultraviolet light from stars. Complex molecules, including organic molecules, form naturally both in space and on planets. Organic molecules on the early Earth could have had either terrestrial origins, with organic molecule synthesis driven by impact shocks or by other energy sources, such as ultraviolet light, redox coupling, or electrical discharges; or extraterrestrial origins (pseudo-panspermia), with organic molecules formed in interstellar dust clouds raining down on to the planet.
Observed extraterrestrial organic moleculesEdit
An organic compound is a chemical whose molecules contain carbon. Carbon is abundant in the Sun, stars, comets, and in the atmospheres of most planets. Organic compounds are relatively common in space, formed by "factories of complex molecular synthesis" which occur in molecular clouds and circumstellar envelopes, and chemically evolve after reactions are initiated mostly by ionizing radiation.Purine and pyrimidinenucleobases including guanine, adenine, cytosine, uracil and thymine have been found in meteorites. These could have provided the materials for DNA and RNA to form on the early Earth. The amino acid glycine was found in material ejected from comet Wild 2; it had earlier been detected in meteorites. Comets are encrusted with dark material, thought to be a tar-like organic substance formed from simple carbon compounds under ionizing radiation. A rain of material from comets could have brought such complex organic molecules to Earth. It is estimated that during the Late Heavy Bombardment, meteorites may have delivered up to five million tons of organic prebiotic elements to Earth per year.
The PAH world hypothesis posits PAHs as precursors to the RNA world. A star, HH 46-IR, resembling the sun early in its life, is surrounded by a disk of material which contains molecules including cyanide compounds, hydrocarbons, and carbon monoxide. PAHs in the interstellar medium can be transformed through hydrogenation, oxygenation, and hydroxylation to more complex organic compounds used in living cells.
The majority of organic compounds introduced on Earth by interstellar dust particles have helped to form complex molecules, thanks to their peculiar surface-catalytic activities. Studies of the 12C/13C isotopic ratios of organic compounds in the Murchison meteorite suggest that the RNA component uracil and related molecules, including xanthine, were formed extraterrestrially. NASA studies of meteorites suggest that all four DNA nucleobases (adenine, guanine and related organic molecules) have been formed in outer space. The cosmic dust permeating the universe contains complex organics ("amorphous organic solids with a mixed aromatic–aliphatic structure") that could be created rapidly by stars. Glycolaldehyde, a sugar molecule and RNA precursor, has been detected in regions of space including around protostars and on meteorites.
As early as the 1860s, experiments demonstrated that biologically relevant molecules can be produced from interaction of simple carbon sources with abundant inorganic catalysts. The spontaneous formation of complex polymers from abiotically generated monomers under the conditions posited by the "soup" theory is not straightforward. Besides the necessary basic organic monomers, compounds that would have prohibited the formation of polymers were also formed in high concentration during the Miller–Urey and Joan Oró experiments. Biology uses essentially 20 amino acids for its coded protein enzymes, representing a very small subset of the structurally possible products. Since life tends to use whatever is available, an explanation is needed for why the set used is so small.
The Breslow catalytic cycle for formaldehyde dimerization and C2-C6 sugar formation
Alexander Butlerov showed in 1861 that the formose reaction created sugars including tetroses, pentoses, and hexoses when formaldehyde is heated under basic conditions with divalent metal ions like calcium. R. Breslow proposed that the reaction was autocatalytic in 1959.
Nucleobases like guanine and adenine can be synthesized from simple carbon and nitrogen sources like hydrogen cyanide (HCN) and ammonia.Formamide produces all four ribonucleotides when warmed with terrestrial minerals. Formamide is ubiquitous in the Universe, produced by the reaction of water and HCN. It can be concentrated by the evaporation of water. HCN is poisonous only to aerobic organisms (eukaryotes and aerobic bacteria), which did not yet exist. It can play roles in other chemical processes such as the synthesis of the amino acid glycine.
DNA and RNA components including uracil, cytosine and thymine can be synthesized under outer space conditions, using starting chemicals such as pyrimidine found in meteorites. Pyrimidine may have been formed in red giant stars or in interstellar dust and gas clouds. All four RNA-bases may be synthesized from formamide in high-energy density events like extraterrestrial impacts.
Other pathways for synthesizing bases from inorganic materials have been reported. Freezing temperatures are advantageous for the synthesis of purines, due to the concentrating effect for key precursors such as hydrogen cyanide. However, while adenine and guanine require freezing conditions for synthesis, cytosine and uracil may require boiling temperatures. Seven different amino acids and eleven types of nucleobases formed in ice when ammonia and cyanide were left in a freezer for 25 years. S-triazines (alternative nucleobases), pyrimidines including cytosine and uracil, and adenine can be synthesized by subjecting a urea solution to freeze-thaw cycles under a reductive atmosphere, with spark discharges as an energy source. The explanation given for the unusual speed of these reactions at such a low temperature is eutectic freezing, which crowds impurities in microscopic pockets of liquid within the ice, causing the molecules to collide more often.
The lipid world theory postulates that the first self-replicating object was lipid-like. Phospholipids form lipid bilayers in water while under agitation—the same structure as in cell membranes. These molecules were not present on early Earth, but other amphiphilic long-chain molecules also form membranes. These bodies may expand by insertion of additional lipids, and may spontaneously split into two offspring of similar size and composition. The main idea is that the molecular composition of the lipid bodies is a preliminary to information storage, and that evolution led to the appearance of polymers like RNA that store information. Studies on vesicles from amphiphiles that might have existed in the prebiotic world have so far been limited to systems of one or two types of amphiphiles.
A lipid bilayer membrane could be composed of a huge number of combinations of arrangements of amphiphiles. The best of these would have favored 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. Such site/compound pairs are transmissible to the daughter vesicles leading to the emergence of distinct lineages of vesicles, which would have allowed Darwinian natural selection.
A central question in evolution is how simple protocells first arose and differed in reproductive contribution to the following generation, thus driving the evolution of life. A functional protocell has (as of 2014) not yet been achieved in a laboratory setting. Self-assembled vesicles are essential components of primitive cells. The second law of thermodynamics requires that the universe move in a direction in which entropy increases, yet life is distinguished by its great degree of organization. Therefore, a boundary is needed to separate life processes from non-living matter. Irene Chen and Jack W. Szostak suggest that elementary protocells can give rise to cellular behaviors including primitive forms of differential reproduction, competition, and energy storage. Competition for membrane molecules would favor stabilized membranes, suggesting a selective advantage for the evolution of cross-linked fatty acids and even the phospholipids of today. Such micro-encapsulation would allow for metabolism within the membrane and the exchange of small molecules, while retaining large biomolecules inside. Such a membrane is needed for a cell to create its own electrochemical gradient to store energy by pumping ions across the membrane.
Energy and entropyEdit
Life requires a loss of entropy, or disorder, when molecules organize themselves into living matter. The emergence of life and increased complexity does not contradict the second law of thermodynamics, which states that overall entropy never decreases, since a living organism creates order in some places (e.g. its living body) at the expense of an increase of entropy elsewhere (e.g. heat and waste production).
Multiple sources of energy were available for chemical reactions on the early Earth. Heat from geothermal processes is a standard energy source for chemistry. Other examples include sunlight, lightning, atmospheric entries of micro-meteorites, and implosion of bubbles in sea and ocean waves. This has been confirmed by experiments and simulations.
Unfavorable reactions can be driven by highly favorable ones, as in the case of iron-sulfur chemistry. For example, this was probably important for carbon fixation.[a] Carbon fixation by reaction of CO2 with H2S via iron-sulfur chemistry is favorable, and occurs at neutral pH and 100 °C. Iron-sulfur surfaces, which are abundant near hydrothermal vents, can drive the production of small amounts of amino acids and other biomolecules.
In 1961, Peter Mitchell proposed chemiosmosis as a cell's primary system of energy conversion. The mechanism, now ubiquitous in living cells, powers energy conversion in micro-organisms and in the mitochondria of eukaryotes, making it a likely candidate for early life. Mitochondria produce adenosine triphosphate (ATP), the energy currency of the cell used to drive cellular processes such as chemical syntheses. The mechanism of ATP synthesis involves a closed membrane in which the ATP synthase enzyme is embedded. The energy required to release strongly-bound ATP has its origin in protons that move across the membrane. In modern cells, those proton movements are caused by the pumping of ions across the membrane, maintaining an electrochemical gradient. In the first organisms, the gradient could have been provided by the difference in chemical composition between the flow from a hydrothermal vent and the surrounding seawater.
The RNA world hypothesis describes an early Earth with self-replicating and catalytic RNA but no DNA or proteins. Many researchers concur that an RNA world must have preceded the DNA-based life that now dominates. However, RNA-based life may not have been the first to exist. Another model echoes Darwin's "warm little pond" with cycles of wetting and drying.
RNA is central to the translation process. Small RNAs can catalyze all the chemical groups and information transfers required for life. RNA both expresses and maintains genetic information in modern organisms; and the chemical components of RNA are easily synthesized under the conditions that approximated the early Earth, which were very different from those that prevail today. The structure of the ribozyme has been called the "smoking gun", with a central core of RNA and no amino acid side chains within 18 Å of the active site that catalyzes peptide bond formation.
The concept of the RNA world was proposed in 1962 by Alexander Rich, and the term was coined by Walter Gilbert in 1986. There were initial difficulties in the explanation of the abiotic synthesis of the nucleotides cytosine and uracil. Subsequent research has shown possible routes of synthesis; for example, formamide produces all four ribonucleotides and other biological molecules when warmed in the presence of various terrestrial minerals.
The RNA world hypothesis proposes that undirected polymerisation led to the emergence of ribozymes, and in turn to an RNA replicase.
RNA replicase can function as both code and catalyst for further RNA replication, i.e. it can be autocatalytic. Jack Szostak has shown that certain catalytic RNAs can join smaller RNA sequences together, creating the potential for self-replication. The RNA replication systems, which include two ribozymes that catalyze each other's synthesis, showed a doubling time of the product of about one hour, and were subject to Darwinian natural selection under the experimental conditions. If such conditions were present on early Earth, then natural selection would favor the proliferation of such autocatalytic sets, to which further functionalities could be added. Self-assembly of RNA may occur spontaneously in hydrothermal vents. A preliminary form of tRNA could have assembled into such a replicator molecule.
Possible precursors to protein synthesis include the synthesis of short peptide cofactors or the self-catalysing duplication of RNA. It is likely that the ancestral ribosome was composed entirely of RNA, although some roles have since been taken over by proteins. Major remaining questions on this topic include identifying the selective force for the evolution of the ribosome and determining how the genetic code arose.
Eugene Koonin has argued that "no compelling scenarios currently exist for the origin of replication and translation, the key processes that together comprise the core of biological systems and the apparent pre-requisite of biological evolution. The RNA World concept might offer the best chance for the resolution of this conundrum but so far cannot adequately account for the emergence of an efficient RNA replicase or the translation system."
In 2016, a set of 355 genes likely present in the LUCA was identified. A total of 6.1 million prokaryotic genes from Bacteria and Archaea were sequenced, identifying 355 protein clusters from amongst 286,514 protein clusters that were probably common to the LUCA. The results suggest that the LUCA was anaerobic with a Wood–Ljungdahl pathway, nitrogen- and carbon-fixing, thermophilic. Its cofactors suggest dependence upon an environment rich in hydrogen, carbon dioxide, iron, and transition metals. Its genetic material was probably DNA, requiring the 4-nucleotide genetic code, messenger RNA, transfer RNAs, and ribosomes to translate the code into proteins such as enzymes. LUCA likely inhabited an anaerobic hydrothermal vent setting in a geochemically active environment. It was evidently already a complex organism, and must have had precursors; it was not the first living thing. The physiology of LUCA has been in dispute.
Leslie Orgel argued that early translation machinery for the genetic code would be susceptible to error catastrophe. Geoffrey Hoffmann however showed that such machinery can be stable in function against "Orgel's paradox".
Early micro-fossils may have come from a hot world of gases such as methane, ammonia, carbon dioxide and hydrogen sulphide, toxic to much current life. Analysis of the tree of life places thermophilic and hyperthermophilic bacteria and archaea closest to the root, suggesting that life may have evolved in a hot environment. The deep sea or alkaline hydrothermal vent theory posits that life began at submarine hydrothermal vents. Martin and 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".
These form where hydrogen-rich fluids emerge from below the sea floor, as a result of serpentinization of ultra-maficolivine with seawater and a pH interface with carbon dioxide-rich ocean water. 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 exothermic reactions.[b]
Early cell powered by external proton gradient near a deep-sea hydrothermal vent. As long as the membrane (or passive ion channels within it) is permeable to protons, the mechanism can function without ion pumps.
Russell demonstrated that alkaline vents created an abiogenic proton motive forcechemiosmotic gradient, ideal for abiogenesis. Their microscopic compartments "provide a natural means of concentrating organic molecules," composed of iron-sulfur minerals such as mackinawite, endowed these mineral cells with the catalytic properties envisaged by Günter Wächtershäuser. This movement of ions across the membrane depends on a combination of two factors:
Diffusion force caused by concentration gradient—all particles including ions tend to diffuse from higher concentration to lower.
Electrostatic force caused by electrical potential gradient—cations like protons H+ tend to diffuse down the electrical potential, anions in the opposite direction.
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).
The surfaces of mineral particles inside deep-ocean hydrothermal vents have catalytic properties similar to those of enzymes and can create simple organic molecules, such as methanol (CH3OH), formic, acetic and pyruvic acids out of the dissolved CO2 in the water, if driven by an applied voltage or by reaction with H2 or H2S.
The research reported by Martin in 2016 supports the thesis that life arose at hydrothermal vents, that spontaneous chemistry in the Earth's crust driven by rock–water interactions at disequilibrium thermodynamically underpinned life's origin and that the founding lineages of the archaea and bacteria were H2-dependent autotrophs that used CO2 as their terminal acceptor in energy metabolism. Martin suggests, based upon this evidence, that the LUCA "may have depended heavily on the geothermal energy of the vent to survive". Colín-García and colleagues argue that exergonic reactions in hydrothermal vents could provide free energy to promote chemical reactions, and many different minerals. These induce chemical gradients, favoring the interaction between electron donors and acceptors.
Mulkidjanian and co-authors think that the marine environments did not provide the ionic balance and composition universally found in cells, or the ions required by essential proteins and ribozymes found in virtually all living organisms, especially with respect to K+/Na+ ratio, Mn2+, Zn2+ and phosphate concentrations. They argue that the only environments that mimic the needed conditions on Earth are hot springs. Mineral deposits in these environments under an anoxic atmosphere would have suitable pH (while current pools in an oxygenated atmosphere would not), contain precipitates of sulfide minerals that absorb harmful ultraviolet radiation, have wetting/drying cycles that concentrate substrate solutions to concentrations amenable to spontaneous formation of polymers of nucleic acids, polyesters and depsipeptides, created both by chemical reactions in the hydrothermal environment, and by exposure to UV light during transport from vents to adjacent pools. The hypothesized pre-biotic environments are similar to deep-oceanic vent environments, with additional components that help explain peculiarities of the LUCA. Experimental research at hot springs supports this hypothesis, as RNA-like polymers were synthesized after multiple wet-dry cycles and exposure to UV light. These polymers became encapsulated in vesicles after rehydration, which would not happen in saltwater conditions.
In the 1980s, Günter Wächtershäuser and Karl Popper postulated the Iron–sulfur world hypothesis for the evolution of pre-biotic chemical pathways. It traces today's biochemistry to primordial reactions which synthesize organic building blocks from gases. Wächtershäuser systems have a built-in source of energy: iron sulfides such as pyrite. The energy released by oxidising these metal sulfides can support synthesis of organic molecules. Such systems may have evolved into autocatalytic sets constituting self-replicating, metabolically active entities predating modern life forms. Experiments with sulfides in an aqueous environment at 100 °C produced a small yield of dipeptides (0.4% to 12.4%) and a smaller yield of tripeptides (0.10%). However, under the same conditions, dipeptides were quickly broken down.
Several models postulate a primitive metabolism, allowing RNA replication to emerge later. The centrality of the Krebs cycle (citric acid cycle) to energy production in aerobic organisms, and in drawing in carbon dioxide and hydrogen ions in biosynthesis of complex organic chemicals, suggests that it was one of the first parts of the metabolism to evolve. Concordantly, geochemistsJack W. Szostak and Kate Adamala demonstrated that non-enzymatic RNA replication in primitive protocells is only possibly in the presence of weak cation chelators like citric acid. This provides further evidence for the central role of citric acid in primordial metabolism.
Russell has proposed that "the purpose of life is to hydrogenate carbon dioxide" (as part of a "metabolism-first," rather than a "genetics-first," scenario). The physicistJeremy England has argued from general thermodynamic considerations that life was inevitable. An early version of this idea was Oparin's 1924 proposal for self-replicating vesicles. In the 1980s and 1990s came Wächtershäuser's iron–sulfur world theory and Christian de Duve's thioester models. More abstract and theoretical arguments for metabolism without genes include Freeman Dyson's mathematical model and Stuart Kauffman's collectively autocatalytic sets in the 1980s. Kauffman's work has been criticized for ignoring the role of energy in driving biochemical reactions in cells.
Armen Mulkidjanian's zinc world (Zn-world) hypothesis extends Wächtershäuser's pyrite hypothesis. The Zn-world theory proposes that hydrothermal fluids rich in H2S interacting with cold primordial ocean (or Darwin's "warm little pond") water precipitated metal sulfide particles. Oceanic hydrothermal systems have a zonal structure reflected in ancient volcanogenic massive sulfide ore deposits. They reach many kilometers in diameter and date back to the Archean. Most abundant are pyrite (FeS2), chalcopyrite (CuFeS2), and sphalerite (ZnS), with additions of galena (PbS) and alabandite (MnS). ZnS and MnS have a unique ability to store radiation energy, e.g. from ultraviolet light. When replicating molecules were originating, the primordial atmospheric pressure was high enough (>100 bar) to precipitate near the Earth's surface, and ultraviolet irradiation was 10 to 100 times more intense than now; hence the photosynthetic properties mediated by ZnS provided the right energy conditions for the synthesis of informational and metabolic molecules and the selection of photostable nucleobases.
The Zn-world theory has been filled out with evidence for the ionic constitution of the interior of the first proto-cells. In 1926, the Canadian biochemist 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 modern cells. The authors conclude that ubiquitous, and by inference primordial, proteins and functional systems show affinity to and functional requirement for K+, Zn2+, Mn2+, and [PO 4]3− . Geochemical reconstruction shows that this ionic composition could not have existed in the ocean but is compatible with inland geothermal systems. In the oxygen-depleted, CO2-dominated primordial atmosphere, the chemistry of water condensates near geothermal fields would resemble the internal milieu of modern cells. Therefore, precellular evolution may have taken place in shallow "Darwin ponds" lined with porous silicate minerals mixed with metal sulfides and enriched in K+, Zn2+, and phosphorus compounds.
Many biomolecules, such as L-glutamic acid, are asymmetric, and occur in living systems in only one of the two possible forms, in the case of amino acids the left-handed form. Prebiotic chemistry would produce both forms, creating a puzzle for abiogenesis researchers.
Homochirality is the geometric uniformity of materials composed of chiral (non-mirror-symmetric) units. Living organisms use molecules that have the same chirality (handedness): with almost no exceptions, amino acids are left-handed while nucleotides and sugars are right-handed. Chiral molecules can be synthesized, but in the absence of a chiral source or a chiral catalyst, they are formed in a 50/50 (racemic) mixture of both forms. Known mechanisms for the production of non-racemic mixtures from racemic starting materials include: asymmetric physical laws, such as the electroweak interaction; asymmetric environments, such as those caused by circularly polarized light, quartz crystals, or the Earth's rotation, statistical fluctuations during racemic synthesis, and spontaneous symmetry breaking. Once established, chirality would be selected for. A small bias (enantiomeric excess) in the population can be amplified into a large one by asymmetric autocatalysis, such as in the Soai reaction. In asymmetric autocatalysis, the catalyst is a chiral molecule, which means that a chiral molecule is catalyzing its own production. An initial enantiomeric excess, such as can be produced by polarized light, then allows the more abundant enantiomer to outcompete the other. Homochirality may have started in outer space, as on the Murchison meteorite the amino acid L-alanine is more than twice as frequent as its D form, and L-glutamic acid is more than three times as abundant as its D counterpart. Amino acids from meteorites show a left-handed bias, whereas sugars show a predominantly right-handed bias, as found in living organisms, suggesting an abiogenic origin of these compounds.
Reaction 3: Forsterite + water → serpentine + brucite
2Mg2SiO4 + 3H2O → Mg3Si2O5(OH)4 + Mg(OH)2
Reaction 3 describes the hydration of olivine with water only to yield serpentine and Mg(OH)2 (brucite). 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 (Ca2SiO4), the artificial calcium equivalent of forsterite.
Analogy of reaction 3 with belite hydration in ordinary Portland cement: Belite + water → C-S-H phase + portlandite
^ abc"NASA Astrobiology Strategy" (PDF). NASA. 2015. Archived from the original (PDF) on 22 December 2016. Retrieved 24 September 2017.
^Trifonov, Edward N. (17 March 2011). "Vocabulary of Definitions of Life Suggests a Definition". Journal of Biomolecular Structure and Dynamics. 29 (2): 259–266. doi:10.1080/073911011010524992. PMID21875147. S2CID 38476092.
^Voytek, Mary A. (6 March 2021). "About Life Detection". NASA. Retrieved 8 March 2021.
^ abWitzany, Guenther (2016). "Crucial steps to life: From chemical reactions to code using agents" (PDF). BioSystems. 140: 49–57. doi:10.1016/j.biosystems.2015.12.007. PMID26723230. S2CID 30962295.
^ abHowell, Elizabeth (8 December 2014). "How Did Life Become Complex, And Could It Happen Beyond Earth?". Astrobiology Magazine. Archived from the original on 15 February 2018. Retrieved 14 April 2022.
^ abPeretó, Juli (2005). "Controversies on the origin of life" (PDF). International Microbiology. 8 (1): 23–31. PMID15906258. Archived from the original (PDF) on 24 August 2015. Retrieved 1 June 2015.
^Compare: Scharf, Caleb; et al. (18 December 2015). "A Strategy for Origins of Life Research". Astrobiology. 15 (12): 1031–1042. Bibcode:2015AsBio..15.1031S. doi:10.1089/ast.2015.1113. PMC4683543. PMID26684503. What do we mean by the origins of life (OoL)? ... Since the early 20th century the phrase OoL has been used to refer to the events that occurred during the transition from non-living to living systems on Earth, i.e., the origin of terrestrial biology (Oparin, 1924; Haldane, 1929). The term has largely replaced earlier concepts such as abiogenesis (Kamminga, 1980; Fry, 2000).
^ abcWeiss, M. C.; Sousa, F. L.; Mrnjavac, N.; Neukirchen, S.; Roettger, M.; Nelson-Sathi, S.; Martin, W.F. (2016). "The physiology and habitat of the last universal common ancestor" (PDF). Nature Microbiology. 1 (9): 16116. doi:10.1038/NMICROBIOL.2016.116. PMID27562259. S2CID 2997255.
^Tirard, Stephane (20 April 2015). Abiogenesis – Definition. Encyclopedia of Astrobiology. p. 1. doi:10.1007/978-3-642-27833-4_2-4. ISBN 978-3-642-27833-4. Thomas Huxley (1825–1895) used the term abiogenesis in an important text published in 1870. 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. ... Since the end of the nineteenth century, evolutive abiogenesis means increasing complexity and evolution of matter from inert to living state in the abiotic context of evolution of primitive Earth.
^Graham, Robert W. (February 1990). "Extraterrestrial Life in the Universe" (PDF). NASA (NASA Technical Memorandum 102363). Lewis Research Center, Cleveland, Ohio. Archived (PDF) from the original on 3 September 2014. Retrieved 2 June 2015.
^Warmflash, David; Warmflash, Benjamin (November 2005). "Did Life Come from Another World?". Scientific American. 293 (5): 64–71. Bibcode:2005SciAm.293e..64W. doi:10.1038/scientificamerican1105-64. PMID16318028.
^Martin, William F. (January 2003). "On the origins of cells: a hypothesis for the evolutionary transitions from abiotic geochemistry to chemoautotrophic prokaryotes, and from prokaryotes to nucleated cells". Phil. Trans. R. Soc. Lond. A. 358 (1429): 59–83. doi:10.1098/rstb.2002.1183. PMC1693102. PMID12594918.
^Parker, Eric T.; Cleaves, Henderson J.; Dworkin, Jason P.; et al. (5 April 2011). "Primordial synthesis of amines and amino acids in a 1958 Miller H2S-rich spark discharge experiment". PNAS. 108 (14): 5526–5531. Bibcode:2011PNAS..108.5526P. doi:10.1073/pnas.1019191108. PMC3078417. PMID21422282.
^Bada, Jeffrey L.; Lazcano, Antonio (2 May 2003). "Prebiotic Soup – Revisiting the Miller Experiment" (PDF). Science. 300 (5620): 745–746. doi:10.1126/science.1085145. PMID12730584. S2CID 93020326. Archived (PDF) from the original on 4 March 2016. Retrieved 13 June 2015.
^Marigo, Paola; et al. (6 July 2020). "Carbon star formation as seen through the non-monotonic initial–final mass relation". Nature Astronomy. 152 (11): 1102–1110. arXiv:2007.04163. Bibcode:2020NatAs...4.1102M. doi:10.1038/s41550-020-1132-1. S2CID 220403402.
^Kasting, James F. (12 February 1993). "Earth's Early Atmosphere" (PDF). Science. 259 (5097): 920–926. Bibcode:1993Sci...259..920K. doi:10.1126/science.11536547. PMID11536547. S2CID 21134564. Archived from the original (PDF) on 10 October 2015. Retrieved 28 July 2015.
^Morse, John W.; MacKenzie, Fred T. (1998). "Hadean Ocean Carbonate Geochemistry". Aquatic Geochemistry. 4 (3–4): 301–319. Bibcode:1998MinM...62.1027M. doi:10.1023/A:1009632230875. S2CID 129616933.
^Wilde, Simon A.; Valley, John W.; Peck, William H.; Graham, Colin M. (11 January 2001). "Evidence from detrital zircons for the existence of continental crust and oceans on the Earth 4.4 Gyr ago" (PDF). Nature. 409 (6817): 175–178. Bibcode:2001Natur.409..175W. doi:10.1038/35051550. PMID11196637. S2CID 4319774. Archived (PDF) from the original on 5 June 2015. Retrieved 3 June 2015.
^Rosing, Minik T.; Bird, Dennis K.; Sleep, Norman H.; et al. (22 March 2006). "The rise of continents – An essay on the geologic consequences of photosynthesis". Palaeogeography, Palaeoclimatology, Palaeoecology. 232 (2–4): 99–113. Bibcode:2006PPP...232...99R. doi:10.1016/j.palaeo.2006.01.007. Archived (PDF) from the original on 14 July 2015. Retrieved 8 June 2015.
^ abcDodd, Matthew S.; Papineau, Dominic; Grenne, Tor; et al. (1 March 2017). "Evidence for early life in Earth's oldest hydrothermal vent precipitates". Nature. 543 (7643): 60–64. Bibcode:2017Natur.543...60D. doi:10.1038/nature21377. PMID28252057. Archived from the original on 8 September 2017. Retrieved 2 March 2017.
^Sleep, Norman H.; Zahnle, Kevin J.; Kasting, James F.; et al. (9 November 1989). "Annihilation of ecosystems by large asteroid impacts on early Earth". Nature. 342 (6246): 139–142. Bibcode:1989Natur.342..139S. doi:10.1038/342139a0. PMID11536616. S2CID 1137852.
^Furukawa, Yoshihiro; Sekine, Toshimori; Oba, Masahiro; et al. (January 2009). "Biomolecule formation by oceanic impacts on early Earth". Nature Geoscience. 2 (1): 62–66. Bibcode:2009NatGe...2...62F. doi:10.1038/NGEO383.
^Maher, Kevin A.; Stevenson, David J. (18 February 1988). "Impact frustration of the origin of life". Nature. 331 (6157): 612–614. Bibcode:1988Natur.331..612M. doi:10.1038/331612a0. PMID11536595. S2CID 4284492.
^Mann, Adam (24 January 2018). "Bashing holes in the tale of Earth's troubled youth". Nature. 553 (7689): 393–395. Bibcode:2018Natur.553..393M. doi:10.1038/d41586-018-01074-6.
^Schopf, J. William; Kudryavtsev, Anatoliy B.; Czaja, Andrew D.; Tripathi, Abhishek B. (5 October 2007). "Evidence of Archean life: Stromatolites and microfossils". Precambrian Research. 158 (3–4): 141–155. Bibcode:2007PreR..158..141S. doi:10.1016/j.precamres.2007.04.009.
^Djokic, Tara; Van Kranendonk, Martin J.; Campbell, Kathleen A.; Walter, Malcolm R.; Ward, Colin R. (9 May 2017). "Earliest signs of life on land preserved in ca. 3.5 Gao hot spring deposits". Nature Communications. 8: 15263. Bibcode:2017NatCo...815263D. doi:10.1038/ncomms15263. PMC5436104. PMID28486437.
^Schopf, J. William; Kitajima, Kouki; Spicuzza, Michael J.; Kudryavtsev, Anatolly B.; Valley, John W. (2017). "SIMS analyses of the oldest known assemblage of microfossils document their taxon-correlated carbon isotope compositions". PNAS. 115 (1): 53–58. Bibcode:2018PNAS..115...53S. doi:10.1073/pnas.1718063115. PMC5776830. PMID29255053.
^Tyrell, Kelly April (18 December 2017). "Oldest fossils ever found show life on Earth began before 3.5 billion years ago". University of Wisconsin-Madison. Retrieved 18 December 2017.
^Ohtomo, Yoko; Kakegawa, Takeshi; Ishida, Akizumi; et al. (January 2014). "Evidence for biogenic graphite in early Archaean Isua metasedimentary rocks". Nature Geoscience. 7 (1): 25–28. Bibcode:2014NatGe...7...25O. doi:10.1038/ngeo2025.
^Noffke, Nora; Christian, Daniel; Wacey, David; Hazen, Robert M. (16 November 2013). "Microbially Induced Sedimentary Structures Recording an Ancient Ecosystem in the ca. 3.48 Gyo Dresser Formation, Pilbara, Western Australia". Astrobiology. 13 (12): 1103–1124. Bibcode:2013AsBio..13.1103N. doi:10.1089/ast.2013.1030. PMC3870916. PMID24205812.
^Hassenkam, T.; Andersson, M. P.; Dalby, K. N.; Mackenzie, D.M.A.; Rosing, M.T. (2017). "Elements of Eoarchean life trapped in mineral inclusions". Nature. 548 (7665): 78–81. Bibcode:2017Natur.548...78H. doi:10.1038/nature23261. PMID28738409. S2CID 205257931.
^O'Donoghue, James (21 August 2011). "Oldest reliable fossils show early life was a beach". New Scientist. 211: 13. doi:10.1016/S0262-4079(11)62064-2. Archived from the original on 30 June 2015.
^Wacey, David; Kilburn, Matt R.; Saunders, Martin; et al. (October 2011). "Microfossils of sulphur-metabolizing cells in 3.4-billion-year-old rocks of Western Australia". Nature Geoscience. 4 (10): 698–702. Bibcode:2011NatGe...4..698W. doi:10.1038/ngeo1238.
^Bell, Elizabeth A.; Boehnike, Patrick; Harrison, T. Mark; et al. (19 October 2015). "Potentially biogenic carbon preserved in a 4.1 billion-year-old zircon". PNAS. 112 (47): 14518–14521. Bibcode:2015PNAS..11214518B. doi:10.1073/pnas.1517557112. PMC4664351. PMID26483481. Early edition, published online before print.
^Baumgartner, Rafael; Van Kranendonk, Martin; Wacey, David; et al. (2019). "Nano−porous pyrite and organic matter in 3.5-billion-year-old stromatolites record primordial life" (PDF). Geology. 47 (11): 1039–1043. Bibcode:2019Geo....47.1039B. doi:10.1130/G46365.1. S2CID 204258554.
^Djokic, Tara; Van Kranendonk, Martin; Cambell, Kathleen; Walter, Malcolm (2017). "Earliest signs of life on land preserved in ca. 3.5 Ga hot spring deposits". Nature Communications. 3.
^Landau, Elizabeth (12 October 2016). "Building Blocks of Life's Building Blocks Come From Starlight". NASA. Archived from the original on 13 October 2016. Retrieved 13 October 2016.
^ abcdHoover, Rachel (21 February 2014). "Need to Track Organic Nano-Particles Across the Universe? NASA's Got an App for That". Ames Research Center. NASA. Archived from the original on 6 September 2015. Retrieved 22 June 2015.
^Goncharuk, Vladislav V.; Zui, O. V. (February 2015). "Water and carbon dioxide as the main precursors of organic matter on Earth and in space". Journal of Water Chemistry and Technology. 37 (1): 2–3. doi:10.3103/S1063455X15010026. S2CID 97965067.
^Abou Mrad, Ninette; Vinogradoff, Vassilissa; Duvernay, Fabrice; et al. (2015). "Laboratory experimental simulations: Chemical evolution of the organic matter from interstellar and cometary ice analogs". Bulletin de la Société Royale des Sciences de Liège. 84: 21–32. Bibcode:2015BSRSL..84...21A. Archived from the original on 13 April 2015. Retrieved 6 April 2015.
^Oba, Yasuhiro; et al. (26 April 2022). "Identifying the wide diversity of extraterrestrial purine and pyrimidine nucleobases in carbonaceous meteorites". Nature Communications. 13 (2008): 2008. Bibcode:2022NatCo..13.2008O. doi:10.1038/s41467-022-29612-x. PMC9042847. PMID35473908. S2CID 248402205.
^"'Life chemical' detected in comet". BBC News. London. 18 August 2009. Archived from the original on 25 May 2015. Retrieved 23 June 2015.
^"NASA Ames PAH IR Spectroscopic Database". NASA. Archived from the original on 29 June 2015. Retrieved 17 June 2015.
^ abcHudgins, Douglas M.; Bauschlicher, Charles W. Jr.; Allamandola, Louis J. (10 October 2005). "Variations in the Peak Position of the 6.2 μm Interstellar Emission Feature: A Tracer of N in the Interstellar Polycyclic Aromatic Hydrocarbon Population". The Astrophysical Journal. 632 (1): 316–332. Bibcode:2005ApJ...632..316H. CiteSeerX10.1.1.218.8786. doi:10.1086/432495. S2CID 7808613.
^ abcDes Marais, David J.; Allamandola, Louis J.; Sandford, Scott; et al. (2009). "Cosmic Distribution of Chemical Complexity". Ames Research Center. Mountain View, California: NASA. Archived from the original on 27 February 2014. Retrieved 24 June 2015.
^ abCarey, Bjorn (18 October 2005). "Life's Building Blocks 'Abundant in Space'". Space.com. Watsonville, California: Imaginova. Archived from the original on 26 June 2015. Retrieved 23 June 2015.
^Gudipati, Murthy S.; Yang, Rui (1 September 2012). "In-situ Probing of Radiation-induced Processing of Organics in Astrophysical Ice Analogs – Novel Laser Desorption Laser Ionization Time-of-flight Mass Spectroscopic Studies". The Astrophysical Journal Letters. 756 (1): L24. Bibcode:2012ApJ...756L..24G. doi:10.1088/2041-8205/756/1/L24. S2CID 5541727.
^ abGallori, Enzo (June 2011). "Astrochemistry and the origin of genetic material". Rendiconti Lincei. 22 (2): 113–118. doi:10.1007/s12210-011-0118-4. S2CID 96659714. "Paper presented at the Symposium 'Astrochemistry: molecules in space and time' (Rome, 4–5 November 2010), sponsored by Fondazione 'Guido Donegani', Accademia Nazionale dei Lincei."
^Callahan, Michael P.; Smith, Karen E.; Cleaves, H. James, II; et al. (23 August 2011). "Carbonaceous meteorites contain a wide range of extraterrestrial nucleobases". PNAS. 108 (34): 13995–13998. Bibcode:2011PNAS..10813995C. doi:10.1073/pnas.1106493108. PMC3161613. PMID21836052.
^Steigerwald, John (8 August 2011). "NASA Researchers: DNA Building Blocks Can Be Made in Space". Goddard Space Flight Center. NASA. Archived from the original on 23 June 2015. Retrieved 23 June 2015.
^Kwok, Sun; Zhang, Yong (3 November 2011). "Mixed aromatic–aliphatic organic nanoparticles as carriers of unidentified infrared emission features". Nature. 479 (7371): 80–83. Bibcode:2011Natur.479...80K. doi:10.1038/nature10542. PMID22031328. S2CID 4419859.
^Jørgensen, Jes K.; Favre, Cécile; Bisschop, Suzanne E.; et al. (2012). "Detection of the simplest sugar, glycolaldehyde, in a solar-type protostar with ALMA" (PDF). The Astrophysical Journal Letters. 757 (1): L4. arXiv:1208.5498. Bibcode:2012ApJ...757L...4J. doi:10.1088/2041-8205/757/1/L4. S2CID 14205612. Archived (PDF) from the original on 24 September 2015. Retrieved 23 June 2015.
^Furukawa, Yoshihiro; Chikaraishi, Yoshito; Ohkouchi, Naohiko; et al. (13 November 2019). "Extraterrestrial ribose and other sugars in primitive meteorites". PNAS. 116 (49): 24440–24445. Bibcode:2019PNAS..11624440F. doi:10.1073/pnas.1907169116. PMC6900709. PMID31740594.
^Breslow, R. (1959). "On the Mechanism of the Formose Reaction". Tetrahedron Letters. 1 (21): 22–26. doi:10.1016/S0040-4039(01)99487-0.
^Oró, Joan (16 September 1961). "Mechanism of Synthesis of Adenine from Hydrogen Cyanide under Possible Primitive Earth Conditions". Nature. 191 (4794): 1193–1194. Bibcode:1961Natur.191.1193O. doi:10.1038/1911193a0. PMID13731264. S2CID 4276712.
^Robertson, Michael P.; Miller, Stanley L. (29 June 1995). "An efficient prebiotic synthesis of cytosine and uracil". Nature. 375 (6534): 772–774. Bibcode:1995Natur.375..772R. doi:10.1038/375772a0. PMID7596408. S2CID 4351012.
^Fox, Douglas (February 2008). "Did Life Evolve in Ice?". Discover. Archived from the original on 30 June 2008. Retrieved 3 July 2008.
^Levy, Matthew; Miller, Stanley L.; Brinton, Karen; Bada, Jeffrey L. (June 2000). "Prebiotic Synthesis of Adenine and Amino Acids Under Europa-like Conditions". Icarus. 145 (2): 609–613. Bibcode:2000Icar..145..609L. doi:10.1006/icar.2000.6365. PMID11543508.
^Menor-Salván, César; Ruiz-Bermejo, Marta; Guzmán, Marcelo I.; et al. (20 April 2009). "Synthesis of Pyrimidines and Triazines in Ice: Implications for the Prebiotic Chemistry of Nucleobases". Chemistry: A European Journal. 15 (17): 4411–4418. doi:10.1002/chem.200802656. PMID19288488.
^Roy, Debjani; Najafian, Katayoun; von Ragué Schleyer, Paul (30 October 2007). "Chemical evolution: The mechanism of the formation of adenine under prebiotic conditions". PNAS. 104 (44): 17272–17277. Bibcode:2007PNAS..10417272R. doi:10.1073/pnas.0708434104. PMC2077245. PMID17951429.
^Lancet, Doron (30 December 2014). "Systems Prebiology-Studies of the origin of Life". The Lancet Lab. Rehovot, Israel: Department of Molecular Genetics; Weizmann Institute of Science. Archived from the original on 26 June 2015. Retrieved 26 June 2015.
Eigen, Manfred; Schuster, Peter (1978). "The Hypercycle. A Principle of Natural Self-Organization. Part B: The Abstract Hypercycle" (PDF). Naturwissenschaften. 65 (1): 7–41. Bibcode:1978NW.....65....7E. doi:10.1007/bf00420631. S2CID 1812273. Archived from the original (PDF) on 3 March 2016.
Eigen, Manfred; Schuster, Peter (July 1978). "The Hypercycle. A Principle of Natural Self-Organization. Part C: The Realistic Hypercycle" (PDF). Naturwissenschaften. 65 (7): 341–369. Bibcode:1978NW.....65..341E. doi:10.1007/bf00439699. S2CID 13825356. Archived from the original (PDF) on 16 June 2016.
^Markovitch, Omer; Lancet, Doron (Summer 2012). "Excess Mutual Catalysis Is Required for Effective Evolvability". Artificial Life. 18 (3): 243–266. doi:10.1162/artl_a_00064. PMID22662913. S2CID 5236043.
^Onsager, Lars (1931). "Reciprocal Relations in Irreversible Processes I and II". Physical Review. 37 (4): 405. Bibcode:1931PhRv...37..405O. doi:10.1103/PhysRev.37.405.
^Onsager, Lars (1931). "Reciprocal Relations in Irreversible Processes I and II". Physical Review (38): 2265. doi:10.1103/PhysRev.38.2265.
^Prigogine, Ilya (1967). An Introduction to the Thermodynamics of Irreversible Processes. New York: Wiley.
^"Exploring Life's Origins: Protocells". Exploring Life's Origins: A Virtual Exhibit. Arlington County, Virginia: National Science Foundation. Archived from the original on 28 February 2014. Retrieved 18 March 2014.
^ abcChen, Irene A. (8 December 2006). "The Emergence of Cells During the Origin of Life". Science. 314 (5805): 1558–1559. doi:10.1126/science.1137541. PMID17158315.
^Zimmer, Carl (26 June 2004). "What Came Before DNA?". Discover. Archived from the original on 19 March 2014.
^Sharov, Alexei A.; Gordon, Richard (2018). "Life Before Earth". Habitability of the Universe Before Earth: Life Before Earth. Astrobiology Exploring Life on Earth and Beyond. Academic Press. pp. 265–296. doi:10.1016/B978-0-12-811940-2.00011-3. ISBN 9780128119402. S2CID 117048600.
^Ladyman, J.; Lambert, J.; Weisner, K. B. (2013). "What is a Complex System?". European Journal of the Philosophy of Science. 3: 33–67. doi:10.1007/s13194-012-0056-8. S2CID 18787276.
^Bar-Nun, A.; Bar-Nun, N.; Bauer, S. H.; Sagan, Carl (24 April 1970). "Shock Synthesis of Amino Acids in Simulated Primitive Environments". Science. 168 (3930): 470–473. Bibcode:1970Sci...168..470B. doi:10.1126/science.168.3930.470. PMID5436082. S2CID 42467812.
^Anbar, Michael (27 September 1968). "Cavitation during Impact of Liquid Water on Water: Geochemical Implications". Science. 161 (3848): 1343–1344. Bibcode:1968Sci...161.1343A. doi:10.1126/science.161.3848.1343. PMID17831346.
^Dharmarathne, Leena; Grieser, Franz (7 January 2016). "Formation of Amino Acids on the Sonolysis of Aqueous Solutions Containing Acetic Acid, Methane, or Carbon Dioxide, in the Presence of Nitrogen Gas". The Journal of Physical Chemistry A. 120 (2): 191–199. Bibcode:2016JPCA..120..191D. doi:10.1021/acs.jpca.5b11858. PMID26695890.
^Patehebieke, Yeersen; Zhao, Ze-Run; Wang, Su; Xu, Hao-Xing; Chen, Qian-Qian; Wang, Xiao (2021). "Cavitation as a plausible driving force for the prebiotic formation of N9 purine nucleosides". Cell Reports Physical Science. 2 (3): 100375. Bibcode:2021CRPS....200375P. doi:10.1016/j.xcrp.2021.100375. S2CID 233662126.
^Kalson, Natan-Haim; Furman, David; Zeiri, Yehuda (11 September 2017). "Cavitation-Induced Synthesis of Biogenic Molecules on Primordial Earth". ACS Central Science. 3 (9): 1041–1049. doi:10.1021/acscentsci.7b00325. PMC5620973. PMID28979946. S2CID 21409351.
^Benner, S. A.; Bell, E. A.; Biondi, E.; Brasser, R.; Carell, T.; Kim, H.-J.; Mojzsis, S. J.; Omran, A.; Pasek, M. A.; Trail, D. (2020). "When Did Life Likely Emerge on Earth in an RNA-First Process?". ChemSystemsChem. 2 (2). doi:10.1002/syst.201900035.
^* Copley, Shelley D.; Smith, Eric; Morowitz, Harold J. (December 2007). "The origin of the RNA world: Co-evolution of genes and metabolism" (PDF). Bioorganic Chemistry. 35 (6): 430–443. doi:10.1016/j.bioorg.2007.08.001. PMID17897696. Archived (PDF) from the original on 5 September 2013. Retrieved 8 June 2015. The proposal that life on Earth arose from an RNA world is widely accepted.
^Pearce, Ben K. D.; Pudritz, Ralph E.; Semenov, Dmitry A.; Henning, Thomas K. (24 October 2017). "Origin of the RNA world: The fate of nucleobases in warm little ponds". PNAS. 114 (43): 11327–11332. arXiv:1710.00434. Bibcode:2017PNAS..11411327P. doi:10.1073/pnas.1710339114. PMC5664528. PMID28973920.
^Yarus, Michael (April 2011). "Getting Past the RNA World: The Initial Darwinian Ancestor". Cold Spring Harbor Perspectives in Biology. 3 (4): a003590. doi:10.1101/cshperspect.a003590. PMC3062219. PMID20719875.
^Neveu, Marc; Kim, Hyo-Joong; Benner, Steven A. (22 April 2013). "The 'Strong' RNA World Hypothesis: Fifty Years Old". Astrobiology. 13 (4): 391–403. Bibcode:2013AsBio..13..391N. doi:10.1089/ast.2012.0868. PMID23551238.
^Gilbert, Walter (20 February 1986). "Origin of life: The RNA world". Nature. 319 (6055): 618. Bibcode:1986Natur.319..618G. doi:10.1038/319618a0. S2CID 8026658.
^Orgel, Leslie E. (October 1994). "The origin of life on Earth". Scientific American. 271 (4): 76–83. Bibcode:1994SciAm.271d..76O. doi:10.1038/scientificamerican1094-76. PMID7524147.
^Lincoln, Tracey A.; Joyce, Gerald F. (27 February 2009). "Self-Sustained Replication of an RNA Enzyme". Science. 323 (5918): 1229–1232. Bibcode:2009Sci...323.1229L. doi:10.1126/science.1167856. PMC2652413. PMID19131595.
^Joyce, Gerald F. (2009). "Evolution in an RNA world". Cold Spring Harbor Perspectives in Biology. 74 (Evolution: The Molecular Landscape): 17–23. doi:10.1101/sqb.2009.74.004. PMC2891321. PMID19667013.
^Szostak, Jack W. (5 February 2015). "The Origins of Function in Biological Nucleic Acids, Proteins, and Membranes". Chevy Chase, Maryland: Howard Hughes Medical Institute. Archived from the original on 14 July 2015. Retrieved 16 June 2015.
^Vlassov, Alexander V.; Kazakov, Sergei A.; Johnston, Brian H.; et al. (August 2005). "The RNA World on Ice: A New Scenario for the Emergence of RNA Information". Journal of Molecular Evolution. 61 (2): 264–273. Bibcode:2005JMolE..61..264V. doi:10.1007/s00239-004-0362-7. PMID16044244. S2CID 21096886.
^Nussinov, Mark D.; Otroshchenko, Vladimir A.; Santoli, Salvatore (1997). "The emergence of the non-cellular phase of life on the fine-grained clayish particles of the early Earth's regolith". BioSystems. 42 (2–3): 111–118. doi:10.1016/S0303-2647(96)01699-1. PMID9184757.
^Kühnlein, Alexandra; Lanzmich, Simon A.; Brun, Dieter (2 March 2021). "tRNA sequences can assemble into a replicator". eLife. 10. doi:10.7554/eLife.63431. PMC7924937. PMID33648631.
^Boone, David R.; Castenholz, Richard W.; Garrity, George M., eds. (2001). The Archaea and the Deeply Branching and Phototrophic Bacteria. Bergey's Manual of Systematic Bacteriology. Springer. ISBN 978-0-387-21609-6. Archived from the original on 25 December 2014.[page needed]
^Woese, C. R.; Fox, G. E. (1977). "Phylogenetic structure of the prokaryotic domain: the primary kingdoms". PNAS. 7 (11): 5088–5090. Bibcode:1977PNAS...74.5088W. doi:10.1073/pnas.74.11.5088. PMC432104. PMID270744.
^Valas, R. E.; Bourne, P. E. (2011). "The origin of a derived superkingdom: how a gram-positive bacterium crossed the desert to become an archaeon". Biology Direct. 6: 16. doi:10.1186/1745-6150-6-16. PMC3056875. PMID21356104.
^"Early life liked it hot". Nature. 535 (7613): 468. 2016. doi:10.1038/535468b. S2CID 49905802.
^Gogarten, Johann Peter; Deamer, David (25 November 2016). "Is LUCA a thermophilic progenote?". Nature Microbiology. 1 (12): 16229. doi:10.1038/nmicrobiol.2016.229. ISSN 2058-5276. PMID27886195. S2CID 205428194.
^Catchpole, Ryan; Forterre, Patrick (2019). "The evolution of Reverse Gyrase suggests a non-hyperthermophilic Last Universal Common Ancestor". Molecular Biology and Evolution. 36 (12): 2737–2747. doi:10.1093/molbev/msz180. PMC6878951. PMID31504731.
^Berkemer, Sarah J.; McGlynn, Shawn E (8 August 2020). "A New Analysis of Archaea–Bacteria Domain Separation: Variable Phylogenetic Distance and the Tempo of Early Evolution". Molecular Biology and Evolution. 37 (8): 2332–2340. doi:10.1093/molbev/msaa089. PMC7403611. PMID32316034.
^Orgel, Leslie E. (April 1963). "The Maintenance of the Accuracy of Protein Synthesis and its Relevance to Ageing". PNAS. 49 (4): 517–521. Bibcode:1963PNAS...49..517O. doi:10.1073/pnas.49.4.517. PMC299893. PMID13940312.
^ abColín-García, M.; Heredia, A.; Cordero, G.; et al. (2016). "Hydrothermal vents and prebiotic chemistry: a review". Boletín de la Sociedad Geológica Mexicana. 68 (3): 599–620. doi:10.18268/BSGM2016v68n3a13. Archived from the original on 18 August 2017.
^Schirber, Michael (24 June 2014). "Hydrothermal Vents Could Explain Chemical Precursors to Life". NASA Astrobiology: Life in the Universe. NASA. Archived from the original on 29 November 2014. Retrieved 19 June 2015.
^Usher, Oli (27 April 2015). "Chemistry of seabed's hot vents could explain emergence of life" (Press release). University College London. Archived from the original on 20 June 2015. Retrieved 19 June 2015.
^Roldan, Alberto; Hollingsworth, Nathan; Roffey, Anna; et al. (May 2015). "Bio-inspired CO2 conversion by iron sulfide catalysts under sustainable conditions". Chemical Communications. 51 (35): 7501–7504. doi:10.1039/C5CC02078F. PMID25835242. Archived from the original on 20 June 2015. Retrieved 19 June 2015.
^Weiss, Madeline C.; Sousa, Filipa L.; Mrnjavac, Natalia; Neukirchen, Sinje; Roettger, Mayo; Nelson-Sathi, Shijulal; Martin, William F. (25 July 2016). "The physiology and habitat of the last universal common ancestor" (PDF). Nature Microbiology. 1 (9): 16116. doi:10.1038/nmicrobiol.2016.116. PMID27562259. S2CID 2997255.
^Colín-García, María (2016). "Hydrothermal vents and prebiotic chemistry: a review". Boletín de la Sociedad Geológica Mexicana. 68 (3): 599–620. doi:10.18268/BSGM2016v68n3a13. Archived from the original on 18 August 2017.
^Mulkidjanian, Armen Y.; Bychkov, Andrew Yu.; Dibrova, Daria V.; Galperin, Michael Y.; Koonin, Eugene V. (3 April 2012). "Origin of first cells at terrestrial, anoxic geothermal fields". Proceedings of the National Academy of Sciences. 109 (14): E821-30. Bibcode:2012PNAS..109E.821M. doi:10.1073/pnas.1117774109. ISSN 0027-8424. PMC3325685. PMID22331915.
^Chandru, Kuhan; Guttenberg, Nicholas; Giri, Chaitanya; et al. (31 May 2018). "Simple prebiotic synthesis of high diversity dynamic combinatorial polyester libraries". Communications Chemistry. 1 (1). doi:10.1038/s42004-018-0031-1.
^Forsythe, Jay G.; Yu, Sheng-Sheng; Mamajanov, Irena; et al. (17 August 2015). "Ester-Mediated Amide Bond Formation Driven by Wet–Dry Cycles: A Possible Path to Polypeptides on the Prebiotic Earth". Angewandte Chemie International Edition in English. 54 (34): 9871–9875. doi:10.1002/anie.201503792. PMC4678426. PMID26201989.
^Patel, Bhavesh H.; Percivalle, Claudia; Ritson, Dougal J.; Duffy, Colm. D.; Sutherland, John D. (16 March 2015). "Common origins of RNA, protein and lipid precursors in a cyanosulfidic protometabolism". Nature Chemistry. 7 (4): 301–307. Bibcode:2015NatCh...7..301P. doi:10.1038/nchem.2202. ISSN 1755-4330. PMC4568310. PMID25803468.
^Mulkidjanian, Armid; Bychkov, Andrew; Dibrova, Daria; Galperin, Michael; Koonin, Eugene (3 April 2012). "Origin of first cells at terrestrial, anoxic geothermal fields". PNAS. 109 (14): E821–E830. Bibcode:2012PNAS..109E.821M. doi:10.1073/pnas.1117774109. PMC3325685. PMID22331915.
^Damer, Bruce; Deamer, David (1 April 2020). "The Hot Spring Hypothesis for an Origin of Life". Astrobiology. 20 (4): 429–452. Bibcode:2020AsBio..20..429D. doi:10.1089/ast.2019.2045. PMC7133448. PMID31841362.
^Deamer, David (10 February 2021). "Where Did Life Begin? Testing Ideas in Prebiotic Analogue Conditions". Life. 11 (2): 134. doi:10.3390/life11020134. PMC7916457. PMID33578711.
^Yue-Ching Ho, Eugene (July–September 1990). "Evolutionary Epistemology and Sir Karl Popper's Latest Intellectual Interest: A First-Hand Report". Intellectus. 15: 1–3. OCLC 26878740. Archived from the original on 11 March 2012.
^ abKeller, Markus A.; Turchyn, Alexandra V.; Ralser, Markus (25 March 2014). "Non-enzymatic glycolysis and pentose phosphate pathway-like reactions in a plausible Archean ocean". Molecular Systems Biology. 10 (725): 725. doi:10.1002/msb.20145228. PMC4023395. PMID24771084.
^Huber, Claudia; Wächtershäuser, Günter (31 July 1998). "Peptides by Activation of Amino Acids with CO on (Ni,Fe)S Surfaces: Implications for the Origin of Life". Science. 281 (5377): 670–672. Bibcode:1998Sci...281..670H. doi:10.1126/science.281.5377.670. PMID9685253.
^Adamala, Katarzyna; Szostak, Jack W. (29 November 2013). "Nonenzymatic Template-Directed RNA Synthesis Inside Model Protocells". Science. 342 (6162): 1098–1100. Bibcode:2013Sci...342.1098A. doi:10.1126/science.1241888. PMC4104020. PMID24288333.
^Musser, George (23 September 2011). "How Life Arose on Earth, and How a Singularity Might Bring It Down". Observations (Blog). Archived from the original on 17 June 2015. Retrieved 17 June 2015.
^Carroll, Sean (10 March 2010). "Free Energy and the Meaning of Life". Cosmic Variance (Blog). Discover. Archived from the original on 14 July 2015. Retrieved 17 June 2015.
^Fox, Ronald F. (December 1993). "Review of Stuart Kauffman, The Origins of Order: Self-Organization and Selection in Evolution". Biophysical Journal. 65 (6): 2698–2699. Bibcode:1993BpJ....65.2698F. doi:10.1016/s0006-3495(93)81321-3. PMC1226010.
^Orgel, Leslie E. (7 November 2000). "Self-organizing biochemical cycles". PNAS. 97 (23): 12503–12507. Bibcode:2000PNAS...9712503O. doi:10.1073/pnas.220406697. PMC18793. PMID11058157.
^Chandru, Kuhan; Gilbert, Alexis; Butch, Christopher; Aono, Masashi; Cleaves, Henderson James II (21 July 2016). "The Abiotic Chemistry of Thiolated Acetate Derivatives and the Origin of Life". Scientific Reports. 6 (29883): 29883. Bibcode:2016NatSR...629883C. doi:10.1038/srep29883. PMC4956751. PMID27443234.
^Vallee, Yannick; Shalayel, Ibrahim; Ly, Kieu-Dung; Rao, K. V. Raghavendra; Paëpe, Gael De; Märker, Katharina; Milet, Anne (8 November 2017). "At the very beginning of life on Earth: the thiol-rich peptide (TRP) world hypothesis". The International Journal of Developmental Biology. 61 (8–9): 471–478. doi:10.1387/ijdb.170028yv. PMID29139533.
^ abMulkidjanian, Armen Y. (24 August 2009). "On the origin of life in the zinc world: 1. Photosynthesizing, porous edifices built of hydrothermally precipitated zinc sulfide as cradles of life on Earth". Biology Direct. 4: 26. doi:10.1186/1745-6150-4-26. PMC3152778. PMID19703272.
^Mulkidjanian, Armen Y.; Galperin, Michael Y. (24 August 2009). "On the origin of life in the zinc world. 2. Validation of the hypothesis on the photosynthesizing zinc sulfide edifices as cradles of life on Earth". Biology Direct. 4: 27. doi:10.1186/1745-6150-4-27. PMC2749021. PMID19703275.
^Mulkidjanian, Armen Y.; Bychkov, Andrew Yu.; Dibrova, Daria V.; et al. (3 April 2012). "Origin of first cells at terrestrial, anoxic geothermal fields". PNAS. 109 (14): E821–E830. Bibcode:2012PNAS..109E.821M. doi:10.1073/pnas.1117774109. PMC3325685. PMID22331915.
^See also Lankenau 2011, pp. 225–286, interconnecting the "Two RNA worlds" concept, and Davidovich, Chen; Belousoff, Matthew; Bashan, Anat; Yonath, Ada (September 2009). "The evolving ribosome: from non-coded peptide bond formation to sophisticated translation machinery". Research in Microbiology. 160 (7): 487–492. doi:10.1016/j.resmic.2009.07.004. PMID19619641.
^ abPlasson, Raphaël; Kondepudi, Dilip K.; Bersini, Hugues; et al. (August 2007). "Emergence of homochirality in far-from-equilibrium systems: Mechanisms and role in prebiotic chemistry". Chirality. 19 (8): 589–600. doi:10.1002/chir.20440. PMID17559107. "Special Issue: Proceedings from the Eighteenth International Symposium on Chirality (ISCD-18), Busan, Korea, 2006"
^Jafarpour, Farshid; Biancalani, Tommaso; Goldenfeld, Nigel (2017). "Noise-induced symmetry breaking far from equilibrium and the emergence of biological homochirality" (PDF). Physical Review E. 95 (3): 032407. Bibcode:2017PhRvE..95c2407J. doi:10.1103/PhysRevE.95.032407. PMID28415353.
^Shibata, Takanori; Morioka, Hiroshi; Hayase, Tadakatsu; et al. (17 January 1996). "Highly Enantioselective Catalytic Asymmetric Automultiplication of Chiral Pyrimidyl Alcohol". Journal of the American Chemical Society. 118 (2): 471–472. doi:10.1021/ja953066g.
^Soai, Kenso; Sato, Itaru; Shibata, Takanori (2001). "Asymmetric autocatalysis and the origin of chiral homogeneity in organic compounds". The Chemical Record. 1 (4): 321–332. doi:10.1002/tcr.1017. PMID11893072.
^Meierhenrich, Uwe (2008). Amino acids and the asymmetry of life caught in the act of formation. Berlin: Springer. pp. 76–79. ISBN 978-3540768869.
^Mullen, Leslie (5 September 2005). "Building Life from Star-Stuff". Astrobiology Magazine. Archived from the original on 14 July 2015.
General and cited sourcesEdit
Altermann, Wladyslaw (2009). "Introduction: A Roadmap to Fata Morgana?". In Seckbach, Joseph; Walsh, Maud (eds.). From Fossils to Astrobiology: Records of Life on Earth and the Search for Extraterrestrial Biosignatures. Cellular Origin, Life in Extreme Habitats and Astrobiology. Vol. 12. Dordrecht, the Netherlands; London: Springer. ISBN 978-1-4020-8836-0.
Bernal, J. D. (1960). "The Problem of Stages in Biopoesis". In Florkin, M. (ed.). Aspects of the Origin of Life. International Series of Monographs on Pure and Applied Biology. Oxford, UK; New York: Pergamon Press. ISBN 978-1-4831-3587-8.
Bock, Gregory R.; Goode, Jamie A., eds. (1996). Evolution of Hydrothermal Ecosystems on Earth (and Mars?). Ciba Foundation Symposium. Vol. 202. Chichester, UK; New York: John Wiley & Sons. ISBN 978-0-471-96509-1.
Calvin, Melvin (1969). Chemical Evolution: Molecular Evolution Towards the Origin of Living Systems on the Earth and Elsewhere. Oxford, UK: Clarendon Press. ISBN 978-0-19-855342-7. OCLC 25220.
Chaichian, Masud; Rojas, Hugo Perez; Tureanu, Anca (2014). "Physics and Life". Basic Concepts in Physics: From the Cosmos to Quarks. Undergraduate Lecture Notes in Physics. Berlin; Heidelberg: Springer Berlin Heidelberg. doi:10.1007/978-3-642-19598-3_12. ISBN 978-3-642-19597-6. OCLC 900189038. S2CID 115247432.
Chang, Thomas Ming Swi (2007). Artificial Cells: Biotechnology, Nanomedicine, Regenerative Medicine, Blood Substitutes, Bioencapsulation, and Cell/Stem Cell Therapy. Regenerative Medicine, Artificial Cells and Nanomedicine. Vol. 1. Hackensack, New Jersey: World Scientific. ISBN 978-981-270-576-1. OCLC 173522612.
Dalrymple, G. Brent (2001). "The age of the Earth in the twentieth century: a problem (mostly) solved". In Lewis, C.L.E.; Knell, S.J. (eds.). The Age of the Earth: from 4004 BC to AD 2002. Geological Society of London, Special Publications. Geological Society Special Publication. Vol. 190. London: Geological Society of London. pp. 205–221. Bibcode:2001GSLSP.190..205D. doi:10.1144/gsl.sp.2001.190.01.14. ISBN 978-1-86239-093-5. OCLC 48570033. S2CID 130092094.
Huxley, Thomas Henry (1968) . "VIII Biogenesis and Abiogenesis ". Discourses, Biological and Geological. Collected Essays. Vol. VIII (Reprint ed.). New York: Greenwood Press. OCLC 476737627.
Klyce, Brig (22 January 2001). Kingsley, Stuart A.; Bhathal, Ragbir (eds.). Panspermia Asks New Questions. The Search for Extraterrestrial Intelligence (SETI) in the Optical Spectrum III. Vol. 4273. Bellingham, WA: SPIE. doi:10.1117/12.435366. ISBN 0-8194-3951-7. Retrieved 9 June 2015. Proceedings of the SPIE held at San Jose, California, 22–24 January 2001
Lane, Nick (2009). Life Ascending: The 10 Great Inventions of Evolution (1st American ed.). New York: W.W. Norton & Company. ISBN 978-0-393-06596-1. OCLC 286488326.
Lankenau, Dirk-Henner (2011). "Two RNA Worlds: Toward the Origin of Replication, Genes, Recombination and Repair". In Egel, Richard; Lankenau, Dirk-Henner; Mulkidjanian, Armen Y. (eds.). Origins of Life: The Primal Self-Organization. Heidelberg: Springer. doi:10.1007/978-3-642-21625-1. ISBN 978-3-642-21624-4. OCLC 733245537.
Lennox, James G. (2001). Aristotle's Philosophy of Biology: Studies in the Origins of Life Science. Cambridge Studies in Philosophy and Biology. Cambridge, UK; New York: Cambridge University Press. ISBN 978-0-521-65976-5.
Michod, Richard E. (1999). Darwinian Dynamics: Evolutionary Transitions in Fitness and Individuality. Princeton, NJ: Princeton University Press. ISBN 978-0-691-02699-2. OCLC 38948118.
Oparin, A.I. (1953) [Originally published 1938; New York: The Macmillan Company]. The Origin of Life. Translation and new introduction by Sergius Morgulis (2nd ed.). Mineola, NY: Dover Publications. ISBN 978-0-486-49522-4.
Sheldon, Robert B. (22 September 2005). "Historical Development of the Distinction between Bio- and Abiogenesis" (PDF). In Hoover, Richard B.; Levin, Gilbert V.; Rozanov, Alexei Y.; Gladstone, G. Randall (eds.). Astrobiology and Planetary Missions. Astrobiology and Planetary Missions. Vol. 5906. Bellingham, WA: SPIE. pp. 59061I. doi:10.1117/12.663480. ISBN 978-0-8194-5911-4. Proceedings of the SPIE held at San Diego, California, 31 July–2 August 2005