Pre-Cambrian stromatolites in the Siyeh Formation, Glacier National Park. In 2002, William Schopf of UCLA published a paper in the scientific journal Nature arguing that geological formations such as this possess 3.5 billion year old fossilized algae microbes.^[1] If true, they would be the earliest known life on earth.

In the natural sciences, abiogenesis, or origin of life, is the study of how life on Earth emerged from inanimate organic and inorganic molecules. Scientific research theorizes that abiogenesis occurred sometime between 4.4 billion years ago, when water vapor first liquefied,^[2] and 2.7 billion years ago, when the ratio of stable isotopes of carbon (¹²C and ¹³C), iron (⁵⁶Fe, ⁵⁷Fe, and ⁵⁸Fe) and sulfur (³²S, ³³S, ³⁴S, and ³⁶S) points to a biogenic origin of minerals and sediments^[3][4] and molecular biomarkers indicate photosynthesis.^[5][6] A creation myth is a supernatural mytho-religious story or explanation that describes the beginnings of humanity, earth, life, and the universe (cosmogony),[1] usually as a deliberate act of creation by a supreme being. ... |Pre-Cambrian stromatolites in the Siyeh Formation, Glacier National Park File links The following pages link to this file: Evolution Origin of life Panspermia Stromatolite ... |Pre-Cambrian stromatolites in the Siyeh Formation, Glacier National Park File links The following pages link to this file: Evolution Origin of life Panspermia Stromatolite ... The Precambrian or Cryptozoic is the period of the geologic timescale from the formation of Earth around 4500 million years before the present (BP) to the evolution of abundant macroscopic hard-shelled fossils, which marked the beginning of the Cambrian, some 542 million years BP. Remarkably little is known about... Pre-Cambrian stromatolites in the Siyeh Formation, Glacier National Park. ... For the non-adjoining national park by the same name in British Columbia, see Glacier National Park (Canada). ... Binomial name Ucla xenogrammus Holleman, 1993 The largemouth triplefin, Ucla xenogrammus, is a fish of the family Tripterygiidae and only member of the genus Ucla, found in the Pacific Ocean from Viet Nam, the Philippines, Palau and the Caroline Islands to Papua New Guinea, Australia (including Christmas Island), and the... Nature, Science and PNAS In academic publishing, a scientific journal is a periodical publication intended to further the progress of science, usually by reporting new research. ... Nature is a prominent scientific journal, first published on 4 November 1869. ... For other uses of the term, see Fossil (disambiguation) Fossils are the mineralized remains of animals or plants or other artifacts such as footprints. ... For the programming language, see algae (programming language). ... The term natural science as the way in which different fields of study are defined is determined as much by historical convention as by the present day meaning of the words. ... This article is about life in general. ... This article is about Earth as a planet. ... Look up animate, inanimate in Wiktionary, the free dictionary. ... Organic may refer to: Look up organic in Wiktionary, the free dictionary. ... Inorganic chemistry is the branch of chemistry concerned with the properties and reactions of inorganic compounds. ... In science, a molecule is the smallest particle of a pure chemical substance that still retains its chemical composition and properties. ... One thousand million (1,000,000,000) is the natural number following 999,999,999 and preceding 1,000,000,001. ... Impact from a water drop causes an upward rebound jet surrounded by circular capillary waves. ... Isotopes are atoms of a chemical element whose nuclei have the same atomic number, Z, but different atomic weights, A. The word isotope, meaning at the same place, comes from the fact that isotopes are located at the same place on the periodic table. ... For other uses, see Carbon (disambiguation). ... Carbon 12 is a stable isotope of the element carbon. ... Carbon-13 is a stable isotope of carbon. ... Fe redirects here. ... This article is about the chemical element. ... Photosynthesis splits water to liberate O2 and fixes CO2 into sugar The leaf is the primary site of photosynthesis in plants. ...

Abiogenesis is a limited field of research despite its profound impact on biology and human understanding of the natural world. Progress in this field is generally slow and sporadic, though it still draws the attention of many due to the eminence of the question being investigated. Several hypotheses have been proposed, most notably the iron-sulfur world theory (metabolism first) and the RNA world hypothesis (genetics first).^[7] For other uses, see Biology (disambiguation). ... The iron-sulfur world theory is a hypothesis for the origin of life advanced by Günter Wächtershäuser, a Munich chemist and patent lawyer, involving forms of iron and sulfur. ... RNA with its nitrogenous bases to the left and DNA to the right. ...

History of the concept in science

Aleksandr Oparin (right) at the laboratory

Until the early 19th century people frequently believed in spontaneous generation of life from non-living matter. Image File history File linksMetadata No higher resolution available. ... Image File history File linksMetadata No higher resolution available. ... Aleksandr Oparin Alexander Ivanovich Oparin (Russian: ) (March 2 [O.S. February 18] 1894 – April 21, 1980) was a Soviet biochemist and author of the theory of the origin of life. ...

Spontaneous generation

Classical notions of abiogenesis, now more precisely known as spontaneous generation, held that complex, living organisms are generated by decaying organic substances, e.g. that mice spontaneously appear in stored grain or maggots spontaneously appear in meat. Domains and Kingdoms Nanobes Acytota Cytota Bacteria Neomura Archaea Eukaryota Bikonta Apusozoa Rhizaria Excavata Archaeplastida Rhodophyta Glaucophyta Plantae Heterokontophyta Haptophyta Cryptophyta Alveolata Unikonta Amoebozoa Opisthokonta Choanozoa Fungi Animalia An ericoid mycorrhizal fungus Life on Earth redirects here. ... This article is about the rodent. ...

According to Aristotle it was a readily observable truth that aphids arise from the dew which falls on plants, fleas from putrid matter, mice from dirty hay, crocodiles from rotting logs at the bottom of bodies of water, and so forth. In the 17th century such assumptions started to be questioned; such as that by Sir Thomas Browne in his Pseudodoxia Epidemica, subtitled Enquiries into Very many Received Tenets, and Commonly Presumed Truths, of 1646, an attack on false beliefs and "vulgar errors." His conclusions were not widely accepted, e.g. his contemporary, Alexander Ross wrote: "To question this (i.e., spontaneous generation) is to question reason, sense and experience. If he doubts of this let him go to Egypt, and there he will find the fields swarming with mice, begot of the mud of Nylus, to the great calamity of the inhabitants."^[8] For other uses, see Aristotle (disambiguation). ... Families There are 10 families: Anoeciidae Aphididae Drepanosiphidae Greenideidae Hormaphididae Lachnidae Mindaridae Pemphigidae Phloeomyzidae Thelaxidae Aphids, also known as greenfly or plant lice, are minute plant-feeding insects. ... For other uses, see Flea (disambiguation). ... Sir Thomas Browne (October 19, 1605 - October 19, 1682) was an English author of varied works that disclose his wide learning in diverse fields including medicine, religion, science and the esoteric. ... Sir Thomas Brownes vast work refuting the common errors and superstitions of his age, Pseudodoxia Epidemica, first appeared in 1646 and went through five editions, the last revision occurring in 1672. ... Alexander Ross (c. ... For other uses, see Nile (disambiguation). ...

In 1546 the physician Girolamo Fracastoro theorized that epidemic diseases were caused by tiny, invisible particles or "spores", which might not be living creatures, but this was not widely accepted. Next, Robert Hooke published the first drawings of a microorganism in 1665. He is also credited for naming the cell which he discovered while observing cork samples. Girolamo Fracastoro (Fracastorius) (1478‑1553) was an Italian physician, scholar and poet. ... Robert Hooke, FRS (July 18, 1635 – March 3, 1703) was an English polymath who played an important role in the scientific revolution, through both experimental and theoretical work. ...

Then in 1676 Anthony van Leeuwenhoek discovered microorganisms that, based on his drawings and descriptions are thought to have been protozoa and bacteria. This sparked a renewal in interest in the microscopic world.^[9] Anton van Leeuwenhoek Anton van Leeuwenhoek (October 24, 1632 - August 26, 1723) was a tradesman and scientist from Delft, in the Netherlands. ... Leishmania donovani, (a species of protozoan) in a bone marrow cell Protozoa (in Greek proton = first and zoa = animals) are unicellular eukaryotes, (singular protozoan). ... Phyla Actinobacteria Aquificae Chlamydiae Bacteroidetes/Chlorobi Chloroflexi Chrysiogenetes Cyanobacteria Deferribacteres Deinococcus-Thermus Dictyoglomi Fibrobacteres/Acidobacteria Firmicutes Fusobacteria Gemmatimonadetes Lentisphaerae Nitrospirae Planctomycetes Proteobacteria Spirochaetes Thermodesulfobacteria Thermomicrobia Thermotogae Verrucomicrobia Bacteria (singular: bacterium) are unicellular microorganisms. ...

The first step was taken by the Italian Francesco Redi, who, in 1668, proved that no maggots appeared in meat when flies were prevented from laying eggs. From the 17th century onwards it was gradually shown that, at least in the case of all the higher and readily visible organisms, the previous sentiment regarding spontaneous generation was false. The alternative seemed to be omne vivum ex ovo: that every living thing came from a pre-existing living thing (literally, everything from an egg). Redi is featured in many modern-day science textbooks due to his experiment. ... Look up maggot in Wiktionary, the free dictionary. ... Omne vivum ex ovo is Latin for All live [is] from [an] egg. This is a foundational concept of modern biology. ...

In 1768 Lazzaro Spallanzani proved that microbes came from the air, and could be killed by boiling. Yet it was not until 1861 that Louis Pasteur performed a series of careful experiments which proved that organisms such as bacteria and fungi do not appear in nutrient rich media of their own accord in non-living material, and which supported cell theory. Lazzaro Spallanzani. ... A microorganism or microbe is an organism that is so small that it is microscopic (invisible to the naked eye). ... Louis Pasteur (December 27, 1822 – September 28, 1895) was a French chemist and microbiologist best known for his remarkable breakthroughs in the causes and prevention of disease. ... A prokaryote Cell theory refers to the idea that cells are the basic unit of structure in all living things. ...

Darwin and Pasteur

By the middle of the 19th century Pasteur and other scientists demonstrated that living organisms did not arise spontaneously from non-living matter; the question therefore arose of how life might have come about within a naturalistic framework. In a letter to Joseph Dalton Hooker on February 1, 1871,^[10] Charles Darwin made the suggestion that the original spark of life may have begun in a "warm little pond, with all sorts of ammonia and phosphoric salts, lights, heat, electricity, etc. present, so that a protein compound was chemically formed ready to undergo still more complex changes". He 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."^[11] In other words, the presence of life itself makes the search for the origin of life dependent on the sterile conditions of the laboratory. Louis Pasteur (December 27, 1822 – September 28, 1895) was a French microbiologist and chemist who demonstrated the germ theory of disease and developed techniques of inoculation, most notably the first vaccine against rabies. ... This article is about methodological naturalism. ... Joseph Dalton Hooker Joseph Dalton Hooker Sir Joseph Dalton Hooker, GCSI, OM, FRS, MD (June 30, 1817 – December 10, 1911) was an English botanist and traveller. ... is the 32nd day of the year in the Gregorian calendar. ... 1871 (MDCCCLXXI) was a common year starting on Sunday (see link for calendar). ... For other people of the same surname, and places and things named after Charles Darwin, see Darwin. ...

Haldane and Oparin

No real progress was made until 1924 when Aleksandr Ivanovich Oparin reasoned that atmospheric oxygen prevented the synthesis of the organic molecules that are the necessary building blocks for the evolution of life. In his The Origin of Life,^[12][13] Oparin argued that a "primeval soup" of organic molecules could be created in an oxygen-less atmosphere through the action of sunlight. These would combine in ever-more complex fashions until they formed coacervate droplets. These droplets would "grow" by fusion with other droplets, and "reproduce" through fission into daughter droplets, and so have a primitive metabolism in which those factors which promote "cell integrity" survive, those that do not become extinct. Many modern theories of the origin of life still take Oparin's ideas as a starting point. Around the same time J. B. S. Haldane also suggested that the earth's pre-biotic oceans – very different from their modern counterparts – would have formed a "hot dilute soup" in which organic compounds, the building blocks of life, could have formed. This idea was called biopoiesis or biopoesis, the process of living matter evolving from self-replicating but nonliving molecules.^[14] Aleksandr Oparin Aleksandr Ivanovich Oparin (Алекса́ндр Ива́нович Опарин, March 2 (February 18 Julian) 1894 – April 21, 1980) was a Soviet biologist and biochemist, who has been acclaimed as one of the greatest authorities on the origin of life. ... This article or section contains information that has not been verified and thus might not be reliable. ... The term cell growth is used in two different ways in biology. ... Biological reproduction is the biological process by which new individual organisms are produced. ... Structure of the coenzyme adenosine triphosphate, a central intermediate in energy metabolism. ... John Burdon Sanderson Haldane (November 5, 1892 – December 1, 1964), who normally used J.B.S. as a first name, was a British geneticist and evolutionary biologist. ...

Early conditions

Morse and MacKenzie^[15] have suggested that oceans may have appeared first in the Hadean era, as soon as 200 million years after the Earth was formed, in a hot (100 °C) reducing environment, and that the pH of about 5.8 rose rapidly towards neutral. This has been supported by Wilde^[2] who has pushed the date of the zircon crystals found in the metamorphosed quartzite of Mount Narryer in Western Australia, previously thought to be 4.1–4.2 billion years old, to 4.404 billion years. This means that oceans and continental crust existed within 150 million years of Earth's formation. The name Hadean refers to the geologic period before 3800 million years ago (mya). ... ed|other uses|reduction}} Illustration of a redox reaction Redox (shorthand for reduction/oxidation reaction) describes all chemical reactions in which atoms have their oxidation number (oxidation state) changed. ... For other uses, see PH (disambiguation). ... Zircon is a mineral belonging to the group of nesosilicates. ... -1... The Narryer Gneiss Terrane complex is verifiably the oldest known portion of the crust on Earth. ... The thickness of the Earths crust (km). ...

Despite this, the Hadean environment was one highly hazardous to life. Frequent collisions with large objects, up to 500 kilometres in diameter, would have been sufficient to vaporise the ocean within a few months of impact, with hot steam mixed with rock vapour leading to high altitude clouds completely covering the planet. After a few months the height of these clouds would have begun to decrease but the cloud base would still have been elevated for about the next thousand years. After that, it would have begun to rain at low altitude. For another two thousand years rains would slowly have drawn down the height of the clouds, returning the oceans to their original depth only 3,000 years after the impact event.^[16] The name Hadean refers to the geologic period before 3800 million years ago (mya). ...

The possible Late Heavy Bombardment possibly caused by the movements in position of the Gaseous Giant planets, that pockmarked the moon, and other inner planets (Mercury, Mars, and presumably Earth and Venus), between 3.8 and 4.1 billion years would likely have sterilised the planet if life had already evolved by that time. The Late Heavy Bombardment (LHB) was a period approximately 3. ...

Examining the time interval that could have existed between such devastating environmental events, the interval in time when life might first have bootstrapped itself into existence can be found for different early environments. The study by Maher and Stephenson shows that if the deep marine hydrothermal setting provides a suitable site for the origin of life, abiogenesis could have happened as early as 4000 to 4200 Myr ago, whereas if it occurred at the surface of the earth abiogenesis could only have occurred between 3700 and 4000 Myr.^[17]

Other research suggests a colder start to life. Work on the synthesis of purines has shown that freezing temperatures are advantageous, due to the concentrating effect for key precursors such as HCN.^[18] Research by Stanley Miller and colleagues suggested that while adenine and guanine require freezing conditions for synthesis, cytosine and uracil may require boiling temperatures.^[19] Other research suggests a colder start to life. Research by Stanley Miller showed the ingredients adenine and guanine require freezing conditions to synthesize, but cytosine and uracil require boiling temperatures.^[20] Based on his research he suggested a beginning of life involving freezing conditions and exploding meteorites.^[21] A new article in Discover Magazine points to research by Stanley Miller indicating the formation of seven different amino acids and 11 types of nucleobases in ice when ammonia and cyanide were left in the Antarctic ice from 1972–1997.^[22] This article also describes research by Hauke Trinks showing the formation of RNA molecules 400 bases long under freezing conditions using an RNA template, a single-strand chain of RNA that guides the formation of a new strand of RNA. As that new RNA strand grows, it adheres to the template.^[23] The explanation given for the unusual speed of these reactions at such a low temperature is eutectic freezing. As an ice crystal forms, it stays pure: only molecules of water join the growing crystal, while impurities like salt or cyanide are excluded. These impurities become crowded in microscopic pockets of liquid within the ice, and this crowding causes the molecules to collide more often.^[24] Stanley Lloyd Miller (born March 7, 1930) is an American chemist famous for his role in the Miller-Urey experiment he performed in 1953, while a graduate student. ... Stanley Lloyd Miller (born March 7, 1930) is an American chemist famous for his role in the Miller-Urey experiment he performed in 1953, while a graduate student. ... For the programming language Adenine, see Adenine (programming language). ... Guanine is one of the five main nucleobases found in the nucleic acids DNA and RNA; the others being adenine, cytosine, thymine, and uracil. ... Cytosine is one of the 5 main nucleobases used in storing and transporting genetic information within a cell in the nucleic acids DNA and RNA. It is a pyrimidine derivative, with a heterocyclic aromatic ring and two substituents attached (an amine group at position 4 and a keto group at... Uracil is a pyrimidine which is common and naturally occurring. ... Discover is a science magazine that publishes articles about science for a general audience. ... For other uses, see Ammonia (disambiguation). ... This article is about the chemical compound. ... A eutectic or eutectic mixture is a mixture of two or more phases at a composition that has the lowest melting point, and where the phases simultaneously crystallise from molten solution at this temperature. ...

Evidence of the early appearance of life comes from the Isua supercrustal belt in Western Greenland and from similar formations in the nearby Akilia Islands. Carbon entering into rock formations has a concentration of elemental δ¹³C of about −5.5, where because of a preferential biotic uptake of ¹²C, biomass has a δ¹³C of between −20 and −30. These isotopic fingerprints are preserved in the sediments, and Mojzis has used this technique to suggest that life existed on the planet already by 3.85 billion years ago.^[25] Lazcano and Miller (1994) suggest that the rapidity of the evolution of life is dictated by the rate of recirculating water through mid-ocean submarine vents. Complete recirculation takes 10 million years, thus any organic compounds produced by then would be altered or destroyed by temperatures exceeding 300 °C. They estimate that the development of a 100 kilobase genome of a DNA/protein primitive heterotroph into a 7000 gene filamentous cyanobacterium would have required only 7 million years.^[26] The Isua Greenstone Belt is an Archean greenstone belt in southwestern Greenland dated at 3. ... Akilia island is in West Greenland, about 22 kilometers south of Nuuk (Godthab), at 63. ... Flowchart to determine if a species is autotroph, heterotroph, or a subtype A heterotroph (Greek heterone = (an)other and trophe = nutrition) is an organism that requires organic substrates to get its carbon for growth and development. ... Orders The taxonomy is currently under revision. ...

Current models

There is no truly "standard model" of the origin of life. But most currently accepted models build in one way or another upon a number of discoveries about the origin of molecular and cellular components for life, which are listed in a rough order of postulated emergence:

1. Plausible pre-biotic conditions result in the creation of certain basic small molecules (monomers) of life, such as amino acids. This was demonstrated in the Miller-Urey experiment by Stanley L. Miller and Harold C. Urey in 1953.
2. Phospholipids (of an appropriate length) can spontaneously form lipid bilayers, a basic component of the cell membrane.
3. The polymerization of nucleotides into random RNA molecules might have resulted in self-replicating ribozymes (RNA world hypothesis).
4. Selection pressures for catalytic efficiency and diversity result in ribozymes which catalyse peptidyl transfer (hence formation of small proteins), since oligopeptides complex with RNA to form better catalysts. Thus the first ribosome is born, and protein synthesis becomes more prevalent.
5. Proteins outcompete ribozymes in catalytic ability, and therefore become the dominant biopolymer. Nucleic acids are restricted to predominantly genomic use.

The origin of the basic biomolecules, while not settled, is less controversial than the significance and order of steps 2 and 3. The basic chemicals from which life is thought to have formed are: 3D (left and center) and 2D (right) representations of the terpenoid molecule atisane. ... A monomer (from Greek mono one and meros part) is a small molecule that may become chemically bonded to other monomers to form a polymer [1]. // Examples of monomers are hydrocarbons such as the alkene and arene homologous series. ... This article is about the class of chemicals. ... The Miller-Urey experiment attempts to recreate the chemical conditions of the primitive Earth in the laboratory, and synthesized some of the building blocks of life. ... Stanley L. Miller (born 1930) is an American chemist famous for his role in the Miller-Urey experiment he performed in 1953, while a graduate student. ... Harold Urey, circa 1963. ... Phospholipid Two schematic representations of a phospholipid. ... This fluid lipid bilayer cross section is made up entirely of phosphatidylcholine. ... The cell membrane (also called the plasma membrane, plasmalemma or phospholipid bilayer) is a selectively permeable lipid bilayer found in all cells. ... A polymer (from Greek: πολυ, polu, many; and μέρος, meros, part) is a substance composed of molecules with large molecular mass composed of repeating structural units, or monomers, connected by covalent chemical bonds. ... A nucleotide is a chemical compound that consists of 3 portions: a heterocyclic base, a sugar, and one or more phosphate groups. ... For other uses, see RNA (disambiguation). ... This article is about the chemical. ... RNA with its nitrogenous bases to the left and DNA to the right. ... For other uses, see Selection (disambiguation). ... The Peptidyl transferase is an aminoacyltransferase (EC 2. ... Figure 1: Ribosome structure indicating small subunit (A) and large subunit (B). ... A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... In biology the genome of an organism is the whole hereditary information of an organism that is encoded in the DNA (or, for some viruses, RNA). ... A representation of the 3D structure of myoglobin, showing coloured alpha helices. ...

1. Methane (CH₄),
2. Ammonia (NH₃),
3. Water (H₂O),
4. Hydrogen sulfide (H₂S),
5. Carbon dioxide (CO₂) or carbon monoxide (CO), and
6. Phosphate (PO₄^3-).

Molecular oxygen (O₂) and ozone (O₃) were either rare or absent. Methane is a chemical compound with the molecular formula . ... For other uses, see Ammonia (disambiguation). ... Impact from a water drop causes an upward rebound jet surrounded by circular capillary waves. ... Hydrogen sulfide (or hydrogen sulphide) is the chemical compound with the formula H2S. This colorless, toxic and flammable gas is responsible for the foul odour of rotten eggs and flatulence. ... Carbon dioxide (chemical formula: ) is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. ... Carbon monoxide, with the chemical formula CO, is a colorless, odorless, and tasteless gas. ... A phosphate, in inorganic chemistry, is a salt of phosphoric acid. ... This article is about the chemical element and its most stable form, or dioxygen. ... For other uses, see Ozone (disambiguation). ...

As of 2008, no one has yet synthesized a "protocell" using basic components which would have the necessary properties of life (the so-called "bottom-up-approach"). Without such a proof-of-principle, explanations have tended to be short on specifics. However, some researchers are working in this field, notably Steen Rasmussen at Los Alamos National Laboratory and Jack Szostak at Harvard University. Others have argued that a "top-down approach" is more feasible. One such approach, attempted by Craig Venter and others at The Institute for Genomic Research, involves engineering existing prokaryotic cells with progressively fewer genes, attempting to discern at which point the most minimal requirements for life were reached. The biologist John Desmond Bernal, coined the term Biopoesis for this process, and suggested that there were a number of clearly defined "stages" that could be recognised in explaining the origin of life. Steen Rasmussen was born in Elsinore, Denmark, in 1955. ... Los Alamos National Laboratory, aerial view from 1995. ... Jack Szostak is an American biologist and Professor of Genetics at Harvard Medical School and Alexander Rich Distinguished Investigator at Massachusetts General Hospital, Boston. ... Harvard redirects here. ... Craig Venter, 2007 J. Craig Venter (born John Craig Venter October 14, 1946, Salt Lake City) is an American biologist and businessman. ... The Institute for Genomic Research (TIGR), is a non-profit genomics research institute founded in 1992 by Craig Venter in Rockville, Maryland, United States. ... John Desmond Bernal (May 10, 1901—September 15, 1971) was an Irish-born scientist (from Nenagh, County Tipperary), known for pioneering X-ray crystallography. ...

• Stage 1: The origin of biological monomers
• Stage 2: The origin of biological polymers
• Stage 3: The evolution from molecules to cell

Bernal suggested that evolution may have commenced early, some time between Stage 1 and 2. In chemistry, a monomer (from Greek mono one and meros part) is a small molecule that may become chemically bonded to other monomers to form a polymer. ... A polymer is a long, repeating chain of atoms, formed through the linkage of many molecules called monomers. ... This article is about evolution in biology. ...

Origin of organic molecules

There are three sources of organic molecules on the early Earth:

1. organic synthesis by other energy sources (such as ultraviolet light or electrical discharges) (eg.Miller's experiments).
2. delivery by extraterrestrial objects (eg carbonaceous chondrites);
3. organic synthesis driven by impact shocks.

Recently estimates of these sources suggest that the heavy bombardment before 3.5 Gyr ago within the early atmosphere made available quantities of organics comparable to those produced by other energy sources.^[27] Chondrules in the chondrite Grassland. ...

The Miller-Urey experiment attempted to recreate the chemical conditions of the primitive Earth in the laboratory, and synthesized some of the building blocks of life.

Replication of the Urey-Miller experiment at NASA-Ames Research Center. ... Replication of the Urey-Miller experiment at NASA-Ames Research Center. ...

Miller's experiment and subsequent work (The Primordial Soup Theory)

Main article: Miller experiment

In 1953 a graduate student, Stanley Miller, and his professor, Harold Urey, performed an experiment that demonstrated how organic molecules could have spontaneously formed on early Earth from inorganic precursors. The now-famous “Miller-Urey experiment” used a highly reduced mixture of gases – methane, ammonia and hydrogen – to form basic organic monomers, such as amino acids.^[28] Whether the mixture of gases used in the Miller-Urey experiment truly reflects the atmospheric content of early Earth is a controversial topic. Other less reducing gases produce a lower yield and variety. It was once thought that appreciable amounts of molecular oxygen were present in the prebiotic atmosphere, which would have essentially prevented the formation of organic molecules; however, the current scientific consensus is that such was not the case. (See Oxygen Catastrophe.)The next most important step in reseach on prebiotic organic synthesis was the deomonstration by John Oró that the nucleic acid purine base, adenine, was formed by the simple heating of solutions of ammonium chanide^[29] The Miller-Urey experiment attempts to recreate the chemical conditions of the primitive Earth in the laboratory, and synthesized some of the building blocks of life. ... Stanley Lloyd Miller (born March 7, 1930) is an American chemist famous for his role in the Miller-Urey experiment he performed in 1953, while a graduate student. ... Harold Urey, circa 1963. ... The early Earth is an term usually defined as Earths first billion years, or gigayear. ... The Miller-Urey experiment attempts to recreate the chemical conditions of the primitive Earth in the laboratory, and synthesized some of the building blocks of life. ... Methane is a chemical compound with the molecular formula . ... For other uses, see Ammonia (disambiguation). ... This article is about the chemistry of hydrogen. ... A monomer (from Greek mono one and meros part) is a small molecule that may become chemically bonded to other monomers to form a polymer [1]. // Examples of monomers are hydrocarbons such as the alkene and arene homologous series. ... The early Earth is an term usually defined as Earths first billion years, or gigayear. ... The Oxygen Catastrophe was a massive environmental change believed to have happened during the Siderian period at the beginning of the Paleoproterozoic era. ...

Simple organic molecules are, of course, a long way from a fully functional self-replicating life form. But in an environment with no pre-existing life these molecules may have accumulated and provided a rich environment for chemical evolution ("soup theory"). On the other hand, the spontaneous formation of complex polymers from abiotically generated monomers under these conditions is not at all a straightforward process. Besides the necessary basic organic monomers, compounds that would have prohibited the formation of polymers were formed in high concentration during the experiments. Self-replication is the process by which some things make copies of themselves. ... Chemical evolution has two meanings and uses. ... A polymer (from Greek: πολυ, polu, many; and μέρος, meros, part) is a substance composed of molecules with large molecular mass composed of repeating structural units, or monomers, connected by covalent chemical bonds. ...

It can be argued that the most crucial challenge unanswered by this theory is how the relatively simple organic building blocks polymerise and form more complex structures, interacting in consistent ways to form a protocell. For example, in an aqueous environment hydrolysis of oligomers/polymers into their constituent monomers would be favored over the condensation of individual monomers into polymers. Also, the Miller experiment produces many substances that would undergo cross-reactions with the amino acids or terminate the peptide chain. Hydrolysis is a chemical reaction or process in which a chemical compound is broken down by reaction with water. ...

The Deep Sea Vent Theory

The deep sea vent theory for the origin of life on Earth states that life may have begun at the interface where chemically rich fluids, heated by some mechanisms like tidal forces of surrounding moons or planets, emerge from below the sea floor. Chemical energy is derived from the reduced gases by the redox reactions, such as hydrogen-sulfide and hydrogen coming out from the vent in contact with a suitable oxidant, such as carbon dioxide^[30]. The most fundamental reactions in chemistry are the redox processes. ...

Fox's experiments

In the 1950s and 1960s, Sidney W. Fox studied the spontaneous formation of peptide structures under conditions that might plausibly have existed early in Earth's history. He demonstrated that amino acids could spontaneously form small peptides. These amino acids and small peptides could be encouraged to form closed spherical membranes, called microspheres.^[31] Sidney W. Fox (24 March 1912 - 10 August 1998) was a Los Angeles-born biochemist. ... Peptides (from the Greek πεπτος, digestible), are the family of short molecules formed from the linking, in a defined order, of various α-amino acids. ... Microspheres or protein protocells are small spherical units postulated by some scientists as a key stage in the origin of life. ...

Eigen's hypothesis

In the early 1970s the problem of the origin of life was approached by Manfred Eigen and Peter Schuster of the Max Planck Institute for Biophysical Chemistry. They examined the transient stages between the molecular chaos and a self-replicating hypercycle in a prebiotic soup.^[32] Manfred Eigen (born May 9, 1927, Bochum) is a German biophysicist and a former director of the Max Planck Institute for Biophysical Chemistry in Göttingen. ... Peter K. Schuster (born March 7, 1941) is a renowned biophysicist, known for his work with Manfred Eigen in developing the quasispecies model. ... The Max Planck Institute for Biophysical Chemistry (Karl-Friedrich Bonhoeffer Institute) is located in Goettingen, Germany. ... The quasispecies [kwaa-zei-spee-seez] model is a description of the process of the Darwinian evolution of self-replicating entities within the framework of physical chemistry. ...

In a hypercycle, the information storing system (possibly RNA) produces an enzyme, which catalyzes the formation of another information system, in sequence until the product of the last aids in the formation of the first information system. Mathematically treated, hypercycles could create quasispecies, which through natural selection entered into a form of Darwinian evolution. A boost to hypercycle theory was the discovery that RNA, in certain circumstances forms itself into ribozymes, capable of catalyzing their own chemical reactions.^[33] However, these reactions are limited to self-excisions (in which a longer RNA molecule becomes shorter), and much rarer small additions that are incapable of coding for any useful protein. The hypercycle theory is further degraded since the hypothetical RNA would require the existence of complex biochemicals such as nucleotides which are not formed under the conditions proposed by the Miller-Urey experiment. The ASCII codes for the word Wikipedia represented in binary, the numeral system most commonly used for encoding computer information. ... For other uses, see RNA (disambiguation). ... Human glyoxalase I. Two zinc ions that are needed for the enzyme to catalyze its reaction are shown as purple spheres, and an enzyme inhibitor called S-hexylglutathione is shown as a space-filling model, filling the two active sites. ... The quasispecies [kwaa-zei-spee-seez] model is a description of the process of the Darwinian evolution of self-replicating entities within the framework of physical chemistry. ... This article is about the chemical. ...

Wächtershäuser's hypothesis

Main article: iron-sulfur world theory

Deep-sea black smoker

Another possible answer to this polymerization conundrum was provided in 1980s by Günter Wächtershäuser, in his iron-sulfur world theory. In this theory, he postulated the evolution of (bio)chemical pathways as fundamentals of the evolution of life. Moreover, he presented a consistent system of tracing today's biochemistry back to ancestral reactions that provide alternative pathways to the synthesis of organic building blocks from simple gaseous compounds. The iron-sulfur world theory is a hypothesis for the origin of life advanced by Günter Wächtershäuser, a Munich chemist and patent lawyer, involving forms of iron and sulfur. ... Image File history File links Download high resolution version (1220x1804, 532 KB) en: Black smoker at a mid-ocean ridge hydrothermal vent de: Black Smoker im Atlantischen Ozean Taken from http://www. ... Image File history File links Download high resolution version (1220x1804, 532 KB) en: Black smoker at a mid-ocean ridge hydrothermal vent de: Black Smoker im Atlantischen Ozean Taken from http://www. ... A black smoker in the Atlantic Ocean Black smokers are a type of hydrothermal vent found on the ocean floor. ... Günter Wächtershäuser, a chemist turned patent lawyer, is mainly known for his groundbreaking and influential work on the origin of life, and in particular his iron-sulfur world theory, a theory that life on Earth had hydrothermal origins. ... The iron-sulfur world theory is a hypothesis for the origin of life advanced by Günter Wächtershäuser, a Munich chemist and patent lawyer, involving forms of iron and sulfur. ...

In contrast to the classical Miller experiments, which depend on external sources of energy (such as simulated lightning or UV irradiation), "Wächtershäuser systems" come with a built-in source of energy, sulfides of iron and other minerals (e.g. pyrite). The energy released from redox reactions of these metal sulfides is not only available for the synthesis of organic molecules, but also for the formation of oligomers and polymers. It is therefore hypothesized that such systems may be able to evolve into autocatalytic sets of self-replicating, metabolically active entities that would predate the life forms known today. Formally, sulfide is the dianion, S2−, which exists in strongly alkaline aqueous solutions formed from H2S or alkali metal salts such as Li2S, Na2S, and K2S. Sulfide is exceptionally basic and, with a pKa > 14, it does not exist in appreciable concentrations even in highly alkaline water. ... Fe redirects here. ... ed|other uses|reduction}} Illustration of a redox reaction Redox (shorthand for reduction/oxidation reaction) describes all chemical reactions in which atoms have their oxidation number (oxidation state) changed. ... In chemistry, an oligomer consists of a finite number of monomer units (oligo is Greek for a few), in contrast to a polymer which, at least in principle, consists of an infinite number of monomers. ... A polymer (from Greek: πολυ, polu, many; and μέρος, meros, part) is a substance composed of molecules with large molecular mass composed of repeating structural units, or monomers, connected by covalent chemical bonds. ... An autocatalytic set is a collection of entities, each of which is able to catalyze the creation of others within the set, such that as a whole, the set was able to catalyze its own replication. ...

The experiment produced a relatively small yield of dipeptides (0.4% to 12.4%) and a smaller yield of tripeptides (0.10%) but the authors also noted that: "under these same conditions dipeptides hydrolysed rapidly."^[34] A dipeptide is a molecule consisting of two amino acids joined by a single peptide bond. ... A tripeptide is a peptide consisting of three amino acids, e. ...

Radioactive beach hypothesis

Zachary Adam^[35] at the University of Washington, Seattle, claims that stronger tidal processes from a much closer moon may have concentrated radioactive 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. According to computer models reported in Astrobiology, vol 7 p 852, a deposit of such radioactive materials could show the same self-sustaining nuclear reaction as that found in the Oklo uranium ore seam in Gabon. Such radioactive beach sand provides sufficient energy to generate organic molecules, such as amino acids and sugars from acetonitrile in water. Radioactive monazite also releases soluble phosphate into regions between sand-grains, making it biologically "accessible". Thus amino acids, sugars and soluble phosphates can all be simultaneously produced, according to Adam. Radioactive actinides, then in greater concentrations, could have formed part of organo-metallic complexes. These complexes could have been important early catalysts to living processes. The University of Washington, founded in 1861, is a public research university in Seattle, Washington. ... This article is about the chemical element. ... Oklo is a place in the West African state of Gabon. ... This article is about the class of chemicals. ... This article is about sugar as food and as an important and widely-traded commodity. ... Acetonitrile is an organic molecule, often used as a solvent, with the chemical formula of CH3CN. Also known as methyl cyanide, it is the simplest of the organic nitriles. ... Monazite powder In geology, the mineral monazite is a reddish-brown phosphate containing rare earth metals and an important source of thorium, lanthanum, and cerium. ... A phosphate, in inorganic chemistry, is a salt of phosphoric acid. ... The actinide (or actinoid) series encompasses the 15 chemical elements that lie between actinium and lawrencium on the periodic table, with atomic numbers 89 - 103[1]. The actinide series derives its name from the first element in the series, actinium. ... A catalyst (Greek: καταλύτης) is a substance that accelerates the rate of a chemical reaction, at some temperature, but without itself being transformed or consumed by the reaction (see also catalysis). ...

John Parnell of the University of Aberdeen suggests that such a process could provide part of the "crucible of life" on 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 believed to have many smaller "platelets" it would provide a suitable environment for such processes.^{[citation needed]} The University of Aberdeen was founded in 1495, in Aberdeen, Scotland. ... The tectonic plates of the world were mapped in the second half of the 20th century. ...

Homochirality

Main article: Homochirality

Some process in chemical evolution must account for the origin of homochirality, i.e. all building blocks in living organisms having the same "handedness" (amino acids being left-handed, nucleic acid sugars (ribose and deoxyribose) being right-handed, and chiral phosphoglycerides). Chiral molecules can be synthesized, but in the absence of a chiral source or a chiral catalyst are formed in a 50/50 mixture of both enantiomers. This is called a racemic mixture. Clark has suggested that homochirality may have started in space, as the studies of the amino acids on the Murchison meteorite showed L-alanine to be more than twice as frequent as its D form, and L-glutamic acid was more than 3 times prevalent than its D counterpart. It is suggested that polarised light has the power to destroy one enantiomer within the proto-planetary disk. Noyes^[36] showed that beta decay caused the breakdown of D-leucine, in a racemic mixture, and that the presence of ¹⁴C, present in larger amounts in organic chemicals in the early Earth environment, could have been the cause. Robert M. Hazen reports upon experiments conducted in which various chiral crystal surfaces, act as sites for possible concentration and assembly of chiral monomer units into macromolecules^[37]. Once established, chirality would be selected for.^[38] Work with organic compounds found on meteorites tends to suggest that chirality is a characteristic of abiogenic synthesis, as amino acids show a left-handed bias, whereas sugars show a predominantly right-handed bias^[39]. Homochirality is a term used to refer to a group of molecules that possess the same sense of chirality. ... Homochirality is a term used to refer to a group of molecules that possess the same sense of chirality. ... In chemistry, an amino acid is any molecule that contains both amino and carboxylic acid functional groups. ... Ribose Ribose, primarily seen as D-ribose, is an aldopentose — a monosaccharide containing five carbon atoms, and including an aldehyde functional group. ... Deoxyribose Deoxyribose, also known as D-Deoxyribose and 2-deoxyribose, is an aldopentose — a monosaccharide containing five carbon atoms, and including an aldehyde functional group. ... Phospholipid Two schematic representations of a phospholipid. ... In chemistry two stereoisomers are said to be enantiomers if one can be superimposed on the mirror image of the other, and vice versa. ... In chemistry, a racemate is a mixture of equal amounts of left- and right-handed stereoisomers of a chiral molecule. ... Fragment of the Murchison meteorite (at right) and isolated individual particles (shown in the test tube). ... This article treats polarization in electrodynamics. ... In chemistry, enantiomers (from the Greek ἐνάντιος, opposite, and μέρος, part or portion) are stereoisomers that are nonsuperimposable complete mirror images of each other, much as ones left and right hands are the same but opposite. ... A proplyd in the Orion Nebula. ... In nuclear physics, beta decay (sometimes called neutron decay) is a type of radioactive decay in which a beta particle (an electron or a positron) is emitted. ... Leucine is one of the 20 most common amino acids and coded for by DNA. It is isomeric with isoleucine. ... In chemistry, a racemate is a mixture of equal amounts of left- and right-handed stereoisomers of a chiral molecule. ... Carbon-14 is the radioactive isotope of carbon discovered February 27, 1940, by Martin Kamen and Sam Ruben. ...

Self-organization and replication

Main article: Self-organization

While features of self-organization and self-replication are often considered the hallmark of living systems, there are many instances of abiotic molecules exhibiting such characteristics under proper conditions. For example Martin and Russel show that physical compartmentation by cell membranes from the environment and self-organization of self-contained redox reactions are the most conserved attributes of living things, and they argue therefore that inorganic matter with such attributes would be life's most likely last common ancestor.^[40] Self-organization refers to a process in which the internal organization of a system, normally an open system, increases automatically without being guided or managed by an outside source. ... Drawing of a cell membrane A component of every biological cell, the cell membrane (or plasma membrane) is a thin and structured bilayer of phospholipid and protein molecules that encapsulate the cell. ... ed|other uses|reduction}} Illustration of a redox reaction Redox (shorthand for reduction/oxidation reaction) describes all chemical reactions in which atoms have their oxidation number (oxidation state) changed. ...

From organic molecules to protocells

The question "How do simple organic molecules form a protocell?" is largely unanswered but there are many hypotheses. Some of these postulate the early appearance of nucleic acids ("genes-first") whereas others postulate the evolution of biochemical reactions and pathways first ("metabolism-first"). Recently, trends are emerging to create hybrid models that combine aspects of both. For other uses, see Gene (disambiguation). ... Structure of the coenzyme adenosine triphosphate, a central intermediate in energy metabolism. ...

"Genes first" models: the RNA world

Main article: RNA world hypothesis

The RNA world hypothesis suggests that relatively short RNA molecules could have spontaneously formed that were capable of catalyzing their own continuing replication. It is difficult to gauge the probability of this formation. A number of theories of modes of formation have been put forward. Early cell membranes could have formed spontaneously from proteinoids, protein-like molecules that are produced when amino acid solutions are heated – when present at the correct concentration in aqueous solution, these form microspheres which are observed to behave similarly to membrane-enclosed compartments. Other possibilities include systems of chemical reactions taking place within clay substrates or on the surface of pyrite rocks. Factors supportive of an important role for RNA in early life include its ability to act both to store information and catalyse chemical reactions (as a ribozyme); its many important roles as an intermediate in the expression and maintenance of the genetic information (in the form of DNA) in modern organisms; and the ease of chemical synthesis of at least the components of the molecule under conditions approximating the early Earth. Relatively short RNA molecules which can duplicate others have been artificially produced in the lab.^[41] RNA with its nitrogenous bases to the left and DNA to the right. ... The RNA world hypothesis proposes that RNA was, before the emergence of the first cell, the dominant, and probably the only, form of life. ... For other uses, see RNA (disambiguation). ... Proteinoids are protein-like molecules formed inorganically from amino acids. ... For other uses, see Clay (disambiguation). ... The mineral pyrite, or iron pyrite, is iron sulfide, FeS2. ... This article is about the chemical. ... The structure of part of a DNA double helix Deoxyribonucleic acid, or DNA, is a nucleic acid molecule that contains the genetic instructions used in the development and functioning of all known living organisms. ...

Researchers have pointed out difficulties for the abiogenic synthesis of nucleotides from cytosine and uracil.^[42] Cytosine has a half-life of 19 days at 100 °C and 17,000 years in freezing water.^[43] Larralde et al, say that "the generally accepted prebiotic synthesis of ribose, the formose reaction, yields numerous sugars without any selectivity."^[44] and they conclude that their "results suggest that the backbone of the first genetic material could not have contained ribose or other sugars because of their instability." The ester linkage of ribose and phosphoric acid in RNA is known to be prone to hydrolysis.^[45] Cytosine is one of the 5 main nucleobases used in storing and transporting genetic information within a cell in the nucleic acids DNA and RNA. It is a pyrimidine derivative, with a heterocyclic aromatic ring and two substituents attached (an amine group at position 4 and a keto group at... Uracil is a pyrimidine which is common and naturally occurring. ...

A slightly different version of this hypothesis is that a different type of nucleic acid, such as PNA, TNA or GNA, was the first one to emerge as a self-reproducing molecule, to be replaced by RNA only later.^[46][47] Look up nucleic acid in Wiktionary, the free dictionary. ... PNA can also refer to the Palestinian National Authority or Pakistan National Alliance. ... TNA is threose nucleic acid, a chemical similar to DNA or RNA but differing in the composition of its backbone. ... Glycerol nucleic acid (GNA) is a chemical similar to DNA or RNA but differing in the composition of its backbone. GNA is not known to occur naturally in existing life on Earth. ...

"Metabolism first" models: iron-sulfur world and others

Several models reject the idea of the self-replication of a "naked-gene" and postulate the emergence of a primitive metabolism which could provide an environment for the later emergence of RNA replication.

One of the earliest incarnations of this idea was put forward in 1924 with Aleksandr Ivanovich Oparin's notion of primitive self-replicating vesicles which predated the discovery of the structure of DNA. More recent variants in the 1980s and 1990s include Günter Wächtershäuser's iron-sulfur world theory and models introduced by Christian de Duve based on the chemistry of thioesters. More abstract and theoretical arguments for the plausibility of the emergence of metabolism without the presence of genes include a mathematical model introduced by Freeman Dyson in the early 1980s and Stuart Kauffman's notion of collectively autocatalytic sets, discussed later in that decade. Aleksandr Oparin Aleksandr Ivanovich Oparin (Алекса́ндр Ива́нович Опарин, March 2 (February 18 Julian) 1894 – April 21, 1980) was a Soviet biologist and biochemist, who has been acclaimed as one of the greatest authorities on the origin of life. ... In cell biology, a vesicle is a relatively small and enclosed compartment, separated from the cytosol by at least one lipid bilayer. ... Günter Wächtershäuser, a chemist turned patent lawyer, is mainly known for his groundbreaking and influential work on the origin of life, and in particular his iron-sulfur world theory, a theory that life on Earth had hydrothermal origins. ... The iron-sulfur world theory is a hypothesis for the origin of life advanced by Günter Wächtershäuser, a Munich chemist and patent lawyer, involving forms of iron and sulfur. ... Christian de Duve (born October 2, 1917) is a biochemist. ... General structure of a thioester. ... Freeman John Dyson FRS (born December 15, 1923) is an English-born American theoretical physicist and mathematician, famous for his work in quantum mechanics, solid-state physics, nuclear weapons design and policy, and for his serious theorizing in futurism and science fiction concepts, including the search for extraterrestrial intelligence. ... Stuart Alan Kauffman (born September 28, 1939) is a theoretical biologist and complex systems researcher, who has given much thought to the origin of life on Earth. ... An autocatalytic set is a collection of entities, each of which is able to catalyze the creation of others within the set, such that as a whole, the set was able to catalyze its own replication. ...

However, the idea that a closed metabolic cycle, such as the reductive citric acid cycle, could form spontaneously (proposed by Günter Wächtershäuser) remains unsupported. According to Leslie Orgel, a leader in origin-of-life studies for the past several decades, there is reason to believe the assertion will remain so. In an article entitled "Self-Organizing Biochemical Cycles",^[48] Orgel summarizes his analysis of the proposal by stating, "There is at present no reason to expect that multistep cycles such as the reductive citric acid cycle will self-organize on the surface of FeS/FeS2 or some other mineral." It is possible that another type of metabolic pathway was used at the beginning of life. For example, instead of the reductive citric acid cycle, the "open" acetyl-CoA pathway (another one of the four recognised ways of carbon dioxide fixation in nature today) would be even more compatible with the idea of self-organisation on a metal sulfide surface. The key enzyme of this pathway, carbon monoxide dehydrogenase/a