Pre-Cambrian stromatolites in the Siyeh Formation, Glacier National Park. In 2002, William Schopf of UCLA published a controversial 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, the question of the origin of life, is the study of how life on Earth might have emerged from non-life. Scientific consensus is 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 and sulfur points to a biogenic origin of minerals and sediments^[3][4] and molecular biomarkers indicate photosynthesis.^[5][6] This topic also includes panspermia and other exogenic theories regarding possible extra-planetary or extra-terrestrial origins of life, thought to have possibly occurred sometime over the last 13.7 billion years in the evolution of the Universe since the Big Bang.^[7] For other uses, see Life (disambiguation). ... Binomial name Mycoplasma genitalium Tully et al. ... This article or section does not adequately cite its references or sources. ... Panspermia is a proven process (based on the principles of Biology, Microbiology, Physics, Chemistry, Astronomy, and assumption that life existed already in the universe) that explains how all life in the universe and/or solar system comes from a seed of life. ... Origin of life can have different meanings depending on the context: Origin of life focuses on modern scientific research on the origin of life. ... Bill Reids sculpture The Raven and The First Men, showing part of a Haida creation story. ... |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. ... Algae have conventionally been regarded as simple plants within the study of botany. ... 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 focuses on the history of thought regarding abiogenesis (the spontaneous generation of life from non-living sources). ... This article is about the tv programme Life on Earth. ... In the physical sciences, non-life is an umbrella term set to distinguish or characterize those inanimate chemical precursors found in the primeval soup of the early years of planetary evolution from which life, theoretically, evolved or came into existence. ... 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. ... For other uses, see Iron (disambiguation). ... This article is about the chemical element. ... The leaf is the primary site of photosynthesis in plants. ... Panspermia is a proven process (based on the principles of Biology, Microbiology, Physics, Chemistry, Astronomy, and assumption that life existed already in the universe) that explains how all life in the universe and/or solar system comes from a seed of life. ... This article is about evolution in biology. ... For other uses, see Universe (disambiguation). ... For other uses, see Big Bang (disambiguation). ...

Origin of life studies 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 theories have been proposed, most notably^[8] RNA world hypothesis. For the song by Girls Aloud see Biology (song) Biology studies the variety of life (clockwise from top-left) E. coli, tree fern, gazelle, Goliath beetle Biology (from Greek: βίος, bio, life; and λόγος, logos, speech lit. ... RNA with its nitrogenous bases to the left and DNA to the right. ...

For the observed evolution of life on earth, see the timeline of life. This timeline outlines the major events in the development of life on planet Earth. ...

History of the concept in science

Aleksandr Oparin (right) at the laboratory

In the early Nineteenth Century and before people frequently believed that life arose spontaneously from non-living matter. Image File history File linksMetadata No higher resolution available. ... Image File history File linksMetadata No higher resolution available. ... Alternative meaning: Nineteenth Century (periodical) (18th century — 19th century — 20th century — more centuries) As a means of recording the passage of time, the 19th century was that century which lasted from 1801-1900 in the sense of the Gregorian calendar. ...

Darwin & Pasteur

By the middle of the 19th century Pasteur and others had 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, 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."^[9] 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. ... For other people of the same surname, and places and things named after Charles Darwin, see Darwin. ...

Haldane & Oparin

No real progress was made until 1924 when Aleksandr Ivanovich Oparin experimentally showed 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 on Earth, 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 fashion until they dissolved into a coacervate droplet. 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. 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 page may meet Wikipedias criteria for speedy deletion. ... 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. ... Biopoiesis or biopoesis is the process of living matter evolving from self-replicating but nonliving molecules. ... Biopoiesis or biopoesis is the process of living matter evolving from self-replicating but nonliving molecules. ...

Early conditions

Morse and MacKenzie ^[10] 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^[11] 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. 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 begins to fall but the cloud base would still be elevated probably for the next thousand years after which at low altitude it starts to rain. For another two thousand years rains slowly draw down the height of the clouds, returning the oceans to their original depth only 3,000 years after the impact event.^[12] 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. 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. ... Quartzite Quartzite (from German Quarzit[1]) is a hard, metamorphic rock which was originally sandstone. ... The Narryer Gneiss Terrane complex is verifiably the oldest known portion of the crust on Earth. ... The thickness of the Earths crust (km). ... The name Hadean refers to the geologic period before 3800 million years ago (mya). ... The Late Heavy Bombardment (LHB) was a period approximately 3. ...

Evidence of the early appearance of life comes from the Isua supercrustal belt in Western Greenland and from similar formations in nearby the Akilia Islands. Carbon entering into rock formations has a concentration of elemental δC¹³ of about -5.5, where because of a preferential biotic uptake of C¹², biomass has a δC¹³ of between -20 and -30. These isotopic fingerprints are preserved in the sediments, and Mojzis^[13] has used this technique to suggest that life existed on the planet already by 3.85 billion years ago. The rapidity of the evolution of life Lazcano and Miller (1994) suggest, is dictated by the fact that all of the ocean's waters is recirculated through mid ocean submarine vents every 10 million years, and any organic compounds produced by then would be altered or destroyed by temperatures exceeding 300 °C. They estimate that the development of an 100 kilobase genome of a DNA/protein primative heterotroph into a 7000 gene filamentous cyanobacteria would have required only 7 million years.^[14] 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. ... 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 was thought to have formed are: 3D (left and center) and 2D (right) representations of the terpenoid molecule atisane. ... 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. ... 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. ... Look up cell membrane in Wiktionary, the free dictionary. ... 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. ... Left: An RNA strand, with its nitrogenous bases. ... // A ribozyme (from ribonucleic acid enzyme, also called RNA enzyme or catalytic RNA) is an RNA molecule that catalyzes a chemical reaction. ... 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. ...

• methane (CH₄),
• ammonia (NH₃),
• water (H₂O),
• hydrogen sulfide (H₂S),
• carbon dioxide (CO₂) or carbon monoxide (CO), and
• 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 (hydrogen sulphide in British English) is the chemical compound with the formula H2S. This colorless, toxic and flammable gas is responsible for the foul odor of rotten eggs and flatulence. ... Carbon dioxide 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. ... General Name, symbol, number oxygen, O, 8 Chemical series nonmetals, chalcogens Group, period, block 16, 2, p Appearance colorless (gas) pale blue (liquid) Standard atomic weight 15. ... For other uses, see Ozone (disambiguation). ...

As of 2007, 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. Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st century. ... 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. ... Dr. Venter on his visit to Hong Kong (December 2004) 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. ... This article focuses on the history of thought regarding abiogenesis (the spontaneous generation of life from non-living sources). ...

• 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 Darwinian 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

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 experiments

Main article: Miller experiment

In 1953 a graduate student, Stanley Miller, and his professor, Harold Urey, performed an experiment that proved 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. 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 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. ... 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. ... 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. ... This page may meet Wikipedias criteria for speedy deletion. ... 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. ...

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. Fox described these formations as protocells, protein spheres that could grow and reproduce.^{[citation needed]} 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. ...

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.^[15] 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, a form of RNA enzyme.^{[citation needed]} The ASCII codes for the word Wikipedia represented in binary, the numeral system most commonly used for encoding computer information. ... Left: An RNA strand, with its nitrogenous bases. ... Ribbon diagram of the enzyme TIM, surrounded by the space-filling model of the protein. ... 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. ... // A ribozyme (from ribonucleic acid enzyme, also called RNA enzyme or catalytic RNA) is an RNA molecule that catalyzes a chemical reaction. ...

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. ... For other uses, see Iron (disambiguation). ... 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."^[16] Another criticism of the result is that the experiment did not include any organic molecules that would most likely cross-react or chain-terminate.^{[citation needed]} A dipeptide is a molecule consisting of two amino acids joined by a single peptide bond. ...

William Martin and Michael Russell reported a modified iron-sulfur-hypothesis in 2002.^[17] According to their scenario, the first cellular life forms may have evolved inside so-called black smokers at seafloor spreading zones in the deep sea. These structures consist of microscale caverns that are coated by thin membraneous metal sulfide walls. Therefore, these structures would solve several critical points of the "pure" Wächtershäuser systems at once: A black smoker in the Atlantic Ocean Black smokers are a type of hydrothermal vent found on the ocean floor. ... The term deep sea refers to those areas of oceans to which little or no light penetrates (the aphotic zone). ...

1. the micro-caverns provide a means of concentrating newly synthesised molecules, thereby increasing the chance of forming oligomers;
2. the steep temperature gradients inside a black smoker allow for establishing "optimum zones" of partial reactions in different regions of the black smoker (e.g. monomer synthesis in the hotter, oligomerisation in the colder parts);
3. the flow of hydrothermal water through the structure provides a constant source of building blocks and energy (freshly precipitated metal sulfides);
4. the model allows for a succession of different steps of cellular evolution (prebiotic chemistry, monomer and oligomer synthesis, peptide and protein synthesis, RNA world, ribonucleoprotein assembly and DNA world) in a single structure, facilitating exchange between all developmental stages;
5. synthesis of lipids as a means of "closing" the cells against the environment is not necessary, until basically all cellular functions are developed.

This model locates the "last universal common ancestor" (LUCA) inside a black smoker, rather than assuming the existence of a free-living form of LUCA. The last evolutionary step would be the synthesis of a lipid membrane that finally allows the organisms to leave the microcavern system of the black smokers and start their independent lives. This postulated late acquisition of lipids is consistent with the presence of completely different types of membrane lipids in archaebacteria and eubacteria (plus eukaryotes) with highly similar cellular physiology of all life forms in most other aspects. Luca or LUCA may refer to: Places Luca, Viqueque, a town in the Subdistrict Viqueque, East Timor San Luca, a town in the Province of Reggio Calabria, Italy People Antonino Saverio De Luca (1805–1883), Italian Cardinal Bonifacio De Luca (1727–1798), Italian poet Ciro de Luca (*1970), Austrian comedian... Figure 1: Basic lipid structure. ... Phyla / Classes Phylum Crenarchaeota Phylum Euryarchaeota     Halobacteria     Methanobacteria     Methanococci     Methanopyri     Archaeoglobi     Thermoplasmata     Thermococci Phylum Korarchaeota Phylum Nanoarchaeota The Archaea are a major group of prokaryotes. ... Subgroups Actinobacteria Aquificae Bacteroidetes/Chlorobi Chlamydiae/Verrucomicrobia Chloroflexi Chrysiogenetes Cyanobacteria Deferribacteres Deinococcus-Thermus Dictyoglomi Fibrobacteres/Acidobacteria Firmicutes Fusobacteria Gemmatimonadetes Nitrospirae Planctomycetes Proteobacteria Spirochaetes Thermodesulfobacteria Thermomicrobia Thermotogae Bacteria (singular: bacterium) are microscopic, unicellular organisms. ... Kingdoms Eukaryotes are organisms with complex cells, in which the genetic material is organized into membrane-bound nuclei. ...

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^[18]. 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. ... Left: An RNA strand, with its nitrogenous bases. ... 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. ... // A ribozyme (from ribonucleic acid enzyme, also called RNA enzyme or catalytic RNA) is an RNA molecule that catalyzes a chemical reaction. ... 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. ...

A slightly different version of this hypothesis is that a different type of nucleic acid, such as PNA or TNA, was the first one to emerge as a self-reproducing molecule, to be replaced by RNA only later^{[19] [20]}. 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. ...

"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. For the rap album, see 1924 (album). ... 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",^[21] 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/acetyl-CoA synthase harbours mixed nickel-iron-sulfur clusters in its reaction centers and catalyses the formation of acetyl-CoA (which may be regarded as a modern form of acetyl-thiol) in a single step. Overview of the citric acid cycle The citric acid cycle (also known as the tricarboxylic acid cycle, the TCA cycle, or the Krebs cycle, after Hans Adolf Krebs who identified the cycle) is a series of chemical reactions of central importance in all living cells that use oxygen as part... Leslie Eleazer Orgel (born Jan 12, 1927 in London) is a chemist. ... Categories: Biochemistry stubs | Thiols ...

Bubble Theory

Waves breaking on the shore create a delicate foam composed of bubbles. Winds sweeping across the ocean have a tendency to drive things to shore, much like driftwood collecting on the beach. It is possible that organic molecules were concentrated on the shorelines in much the same way. Shallow coastal waters also tend to be warmer, further concentrating the molecules through evaporation. While bubbles composed mostly of water burst quickly, water containing amphiphiles forms much more stable bubbles, lending more time to the particular bubble to perform these crucial experiments. “Vaporization” redirects here. ... Amphiphile (from the Greek αμφις, amphis: both and φιλíα, philia: love, friendship) is a term describing a chemical compound possessing both hydrophilic and hydrophobic nature. ...

Amphiphiles are oily compounds containing a hydrophilic head on one or both ends of a hydrophobic molecule. Some amphiphiles have the tendency to spontaneously form membranes in water. A spherically closed membrane contains water and is a hypothetical precursor to the modern cell membrane. If a protein came along that increased the integrity of its parent bubble, then that bubble had an advantage, and was placed at the top of the natural selection waiting list. Primitive reproduction can be envisioned when the bubbles burst, releasing the results of the experiment into the surrounding medium. Once enough of the 'right stuff' was released into the medium, the development of the first prokaryotes, eukaryotes, and multicellular organisms could be achieved.^[22] The adjective hydrophilic describes something that likes water (from Greek hydros = water; philos = friend). ... In chemistry, hydrophobic or lipophilic species, or hydrophobes, tend to be electrically neutral and nonpolar, and thus prefer other neutral and nonpolar solvents or molecular environments. ... For other uses, see Natural selection (disambiguation). ... Prokaryotes are unicellular (in rare cases, multicellular) organisms without a nucleus. ... Kingdoms Eukaryotes are organisms with complex cells, in which the genetic material is organized into membrane-bound nuclei. ...

Similarly, bubbles formed entirely out of protein-like molecules, called microspheres, will form spontaneously under the right conditions. But they are not a likely precursor to the modern cell membrane, as cell membranes are composed primarily of lipid compounds rather than amino-acid compounds (for types of membrane spheres associated with abiogenesis, see protobionts, micelle, coacervate). Microspheres or protein protocells are small spherical units postulated by some scientists as a key stage in the origin of life. ... Protobionts may have been precoursors to prokaryotic cells. ... Schematic of a micelle. ... This article or section contains information that has not been verified and thus might not be reliable. ...

A recent model by Fernando and Rowe^[23] suggests that the enclosure of an autocatalytic non-enzymatic metabolism within protocells may have been one way of avoiding the side-reaction problem that is typical of metabolism first models.

Other models

Autocatalysis

British ethologist Richard Dawkins wrote about autocatalysis as a potential explanation for the origin of life in his 2004 book The Ancestor's Tale. Autocatalysts are substances which catalyze the production of themselves, and therefore have the property of being a simple molecular replicator. In his book, Dawkins cites experiments performed by Julius Rebek and his colleagues at the Scripps Research Institute in California in which they combined amino adenosine and pentafluorophenyl ester with the autocatalyst amino adenosine triacid ester (AATE). One system from the experiment contained variants of AATE which catalysed the synthesis of themselves. This experiment demonstrated the possibility that autocatalysts could exhibit competition within a population of entities with heredity, which could be interpreted as a rudimentary form of natural selection. Ethology is the scientific study of animal behaviour (particularly of social animals such as primates and canids), and is a branch of zoology. ... Clinton Richard Dawkins, FRS (born March 26, 1941) is a British ethologist, evolutionary biologist and popular science writer who holds the Charles Simonyi Chair for the Public Understanding of Science at the University of Oxford. ... A single chemical reaction is said to have undergone autocatalysis, or be autocatalytic, if the reaction product is itself the catalyst for that reaction. ... Year 2004 (MMIV) was a leap year starting on Thursday of the Gregorian calendar. ... The Ancestors Tale cover The Ancestors Tale (subtitled A Pilgrimage to the Dawn of Life) is a 2004 popular science book by Richard Dawkins, with contributions from Dawkins research assistant Yan Wong. ... Julius Rebek Julius Rebek, Jr. ... The Scripps Research Institute, in La Jolla, California is home to notable chemists such as K. Barry Sharpless and P. G. Schultz, as well as neurobiologist Gerald Edelman, and Nobel Laureate Kurt Wurtrich. ... Official language(s) English Capital Sacramento Largest city Los Angeles Largest metro area Greater Los Angeles Area  Ranked 3rd  - Total 158,302 sq mi (410,000 km²)  - Width 250 miles (400 km)  - Length 770 miles (1,240 km)  - % water 4. ... For other uses, see Natural selection (disambiguation). ...

Clay theory

A model for the origin of life based on clay was forwarded by Dr A. Graham Cairns-Smith of the University of Glasgow in 1985 and adopted as a plausible illustration by several other scientists, including Richard Dawkins. Clay theory postulates that complex organic molecules arose gradually on a pre-existing, non-organic replication platform -- silicate crystals in solution. Complexity in companion molecules developed as a function of selection pressures on types of clay crystal is then exapted to serve the replication of organic molecules independently of their silicate "launch stage". It is, truly, "life from a rock." For other uses, see Clay (disambiguation). ... Dr. A. Graham Cairns-Smith (19?? to 20??) is an organic chemist and molecular biologist at Glasgow University, most famous for his controversial 1985 book, Seven Clues to the Origins of Life. ... Master of Theology (MTh) Dentistry Nursing Affiliations Russell Group Universitas 21 Website http://www. ... This article is about the year. ... Clinton Richard Dawkins, FRS (born March 26, 1941) is a British ethologist, evolutionary biologist and popular science writer who holds the Charles Simonyi Chair for the Public Understanding of Science at the University of Oxford. ... Dr. A. Graham Cairns-Smith (19?? to 20??) is an organic chemist and molecular biologist at Glasgow University, most famous for his controversial 1985 book, Seven Clues to the Origins of Life. ... An exaptation is a biological adaptation where the biological function currently performed by the adaptation was not the function performed while the adaptation evolved under earlier pressures of natural selection. ...

Cairns-Smith is a staunch critic of other models of chemical evolution.^[24] However, he admits, that like many models of the origin of life, his own also has its shortcomings (Horgan 1991).

In 2007, Kahr and colleagues reported their experiments to examine the idea that crystals can act as a source of transferable information, using crystals of potassium hydrogen phthalate. "Mother" crystals with imperfections were cleaved and used as seeds to grow "daughter" crystals from solution. They then examined the distribution of imperfections in the crystal system and found that the imperfections in the mother crystals were indeed reproduced in the daughters. The daughter crystals had many additional imperfections. For a gene-like behavior the additional imperfections should be much less than the parent ones, thus Kahr concludes that the crystals "were not faithful enough to store and transfer information form one generation to the next".^[25][26] Potassium hydrogen phthalate, often called simply KHP, is a white, colorless, ionic solid that is the monopotassium salt of phthalic acid. ...

"Deep-hot biosphere" model of Gold

The discovery of nanobes (filamental structures that are smaller than bacteria, but that may contain DNA) in deep rocks, led to a controversial theory put forward by Thomas Gold in the 1990s that life first developed not on the surface of the Earth, but several kilometers below the surface.^{[citation needed]} It is now known that microbial life is plentiful up to five kilometers below the earth's surface^{[citation needed]} in the form of archaea, which are generally considered to have originated either before or around the same time as eubacteria, most of which live on the surface including the oceans. It is claimed that discovery of microbial life below the surface of another body in our solar system would lend significant credence to this theory. He also noted that a trickle of food from a deep, unreachable, source is needed for survival because life arising in a puddle of organic material is likely to consume all of its food and become extinct. A nanobe Nanobes are tiny filamental structures first found in some rocks and sediments. ... Thomas Gold (May 22, 1920 – June 22, 2004) was an Austrian astrophysicist, a professor of astronomy at Cornell University, and a member of the US National Academy of Sciences. ... A microorganism or microbe is an organism that is so small that it is microscopic (invisible to the naked eye). ... Phyla Crenarchaeota Euryarchaeota Korarchaeota Nanoarchaeota ARMAN The Archaea (), or archaebacteria, are a major group of microorganisms. ... Phyla/Divisions Actinobacteria Aquificae Bacteroidetes/Chlorobi Chlamydiae/Verrucomicrobia Chloroflexi Chrysiogenetes Cyanobacteria Deferribacteres Deinococcus-Thermus Dictyoglomi Fibrobacteres/Acidobacteria Firmicutes Fusobacteria Gemmatimonadetes Nitrospirae Omnibacteria Planctomycetes Proteobacteria Spirochaetes Thermodesulfobacteria Thermomicrobia Thermotogae Bacteria (singular, bacterium) are a major group of living organisms. ... This article is about the Solar System. ...

"Primitive" extraterrestrial life

An alternative to Earthly abiogenesis is the hypothesis that primitive life may have originally formed extraterrestrially, either in space or on a nearby planet (Mars). (Note that exogenesis is related to, but not the same as, the notion of panspermia). A supporter of this theory is Francis Crick. Panspermia is a proven process (based on the principles of Biology, Microbiology, Physics, Chemistry, Astronomy, and assumption that life existed already in the universe) that explains how all life in the universe and/or solar system comes from a seed of life. ... Francis Harry Compton Crick OM FRS (8 June 1916 – 28 July 2004) was an English molecular biologist, physicist, and neuroscientist, who is most noted for being one of the co-discoverers of the structure of the DNA molecule in 1953. ...

Organic compounds are relatively common in space, especially in the outer solar system where volatiles are not evaporated by solar heating. Comets are encrusted by outer layers of dark material, thought to be a tar-like substance composed of complex organic material formed from simple carbon compounds after reactions initiated mostly by irradiation by ultraviolet light. It is supposed that a rain of material from comets could have brought significant quantities of such complex organic molecules to Earth. Tar can be produced from corn stalks by heating in a microwave. ... For other uses, see Ultraviolet (disambiguation). ... Comet Hale-Bopp Comet West For other uses, see Comet (disambiguation). ...

An alternative but related hypothesis, proposed to explain the presence of life on Earth so soon after the planet had cooled down, with apparently very little time for prebiotic evolution, is that life formed first on early Mars. Due to its smaller size Mars cooled before Earth (a difference of hundreds of millions of years), allowing prebiotic processes there while Earth was still too hot. Life was then transported to the cooled Earth when crustal material was blasted off Mars by asteroid and comet impacts. Mars continued to cool faster and eventually became hostile to the continued evolution or even existence of life (it lost its atmosphere due to low volcanism), Earth is following the same fate as Mars, but at a slower rate. Mars is the fourth planet from the Sun in the solar system, named after the Roman god of war (the counterpart of the Greek Ares), on account of its blood red color as viewed in the night sky. ...

Neither hypothesis actually answers the question of how life first originated, but merely shifts it to another planet or a comet. However, the advantage of an extraterrestrial origin of primitive life is that life is not required to have evolved on each planet it occurs on, but rather in a single location, and then spread about the galaxy to other star systems via cometary and/or meteorite impact. Evidence to support the plausibility of the concept is scant, but it finds support in recent study of Martian meteorites found in Antarctica and in studies of extremophile microbes.^[27] Additional support comes from a recent discovery of a bacterial ecosytem whose energy source is radioactivity.^[28]

The Lipid World

There is a theory that ascribes the first self-replicating object to be lipid-like.^[29] It is known that phospholipids spontaneously form bilayers in water - the same structure as in cell membranes. These molecules were not present on early earth, however other amphiphilic long chain molecules also form membranes. Furthermore, these bodies may expand (by insertion of additional lipids), and under excessive expansion may undergo spontaneous splitting which preserves the same size and composition of lipids in the two progenies. The main idea in this theory is that the molecular composition of the lipid bodies is the preliminary way for information storage, and evolution led to the appearance of polymer entities such as RNA or DNA that may store information favorably.

The Polyphosphate model

The problem with most scenarios of abiogenesis is that the thermodynamic equilibrium of amino acid versus peptides is in the direction of separate amino acids. What has been missing is some force that drives polymerization. The resolution of this problem may well be in the properties of polyphosphates.^[30][31] Polyphosphates are formed by polymerization of ordinary monophosphate ions PO₄^-3 by ultraviolet light. Polyphosphates cause polymerization of amino acids into peptides. Ample ultraviolet light must have existed in the early oceans. The key issue seems to be that calcium reacts with soluble phosphate to form insoluble calcium phosphate (apatite), so some plausible mechanism must be found to keep free calcium ions from solution. Possibly, the answer may be in some stable, non-reactive complex such as calcium citrate. Calcium phosphate is the name given to a family of minerals containing calcium ions (Ca2+) together with orthophosphates (PO43-), metaphosphates or pyrophosphates (P2O74-) and occasionally hydrogen or hydroxide ions. ... Apatite is a group of phosphate minerals, usually referring to hydroxylapatite, fluorapatite, and chlorapatite, named for high concentrations of OH-, F-, or Cl- ions, respectively, in the crystal. ...

The Ecopoesis model

The Ecopoesis model^[32] proposes that the geochemical cycles of biogenic elements, driven by an early oxygen-rich atmosphere, were the basis of a planetary metabolism that preceded and conditioned the gradual evolution of organismal life.

PAH world hypothesis

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