Pre-Cambrian stromatolites in the Siyeh Formation, Glacier National Park. The Precambrian ( Pre-Cambrian) is an informal name for the supereon comprising the eons of the Geologic timescale that came before the current Stromatolites (from Greek στρώμα strōma, mattress bed stratum and λιθος lithos, rock are layered accretionary Structures formed in Glacier National Park is located in the US state of Montana, bordering the Canadian provinces of Alberta and British Columbia. In 2002, William Schopf of UCLA published a controversial paper in the scientific journal Nature arguing that geological formations such as this possess 3. The University of California Los Angeles (generally known as UCLA) is a public research university located in Westwood Los Angeles, California, United For a broader class of publications which include scientific journals see Academic journal. Nature is a prominent Scientific journal, first published on 4 November 1869 5 billion year old fossilized algae microbes. FOSSIL is a standard protocol for allowing serial communication for Telecommunications programs under the DOS Operating system. Algae ( sing. alga are a large and diverse group of simple typically Autotrophic organisms ranging from Unicellular to Multicellular forms ^[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 emerged from non-life. In Science, the term natural science refers to a naturalistic approach to the study of the Universe, which is understood as obeying rules or law of Life is a state that distinguishes Organisms from non-living objects such as non-life and dead organisms being manifested by growth through Metabolism EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001 Scientific consensus is that abiogenesis occurred sometime between 4. 4 billion years ago, when water vapor first liquefied,^[2] and 2. Water is a common Chemical substance that is essential for the survival of all known forms of Life. 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. Isotopes (Greek isos = "equal" tópos = "site place" are any of the different types of atoms ( Nuclides Carbon (kɑɹbən is a Chemical element with the symbol C and its Atomic number is 6 Carbon-12 is the most abundant of the two stable Isotopes of the element Carbon, accounting for 98 Carbon-13 ( 13C) is a natural stable Isotope of Carbon and one of the Environmental isotopes. Iron (ˈаɪɚn is a Chemical element with the symbol Fe (ferrum and Atomic number 26 Sulfur or sulphur (ˈsʌlfɚ see spelling below) is the Chemical element that has the Atomic number 16 Photosynthesis is a Metabolic pathway that converts Light Energy into Chemical energy. ^[5][6] This topic also includes panspermia and other exogenic theories regarding possible extra-planetary or extraterrestrial origins of life. Panspermia ( Gk. πάς/πάν (pas/pan all and σπέρμα ( sperma, seed is the Hypothesis that "seeds" of Life exist already ^[7]

Abiogenesis is a limited field of research despite its profound impact on biology and human understanding of the natural world. Foundations of modern biology There are five unifying principles 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). The iron-sulfur world theory is a hypothesis for the Origin of life advanced by Günter Wächtershäuser, a Munich chemist and patent lawyer involving The RNA world hypothesis proposes that a world filled with life based on Ribonucleic acid (RNA predated current life based on Deoxyribonucleic acid (DNA ^[8]

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. Alexander Ivanovich Oparin (Алекса́ндр Ива́нович Опарин ( Uglich, Russia &ndash April 21, 1980, Moscow The 19th century of the Common Era began on January 1, 1801 and ended on December 31, 1900, according to the Gregorian calendar

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. A mouse (plural mice) is a small Animal that belongs to one

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. Aristotle (Greek Aristotélēs) (384 BC – 322 BC was a Greek philosopher a student of Plato and teacher of Alexander the Great. Flea is the Common name for any of the small wingless Insects of the order Siphonaptera (some authorities use the name Aphaniptera 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. Sir Thomas Browne ( October 19, 1605 &ndash October 19, 1682) was an English author of varied works which disclose his wide learning Sir Thomas Browne 's vast work refuting the common errors and superstitions of his age Pseudodoxia Epidemica, first appeared in 1646 and went through five subsequent " His conclusions were not widely accepted, e. g. his contemporary, Alexander Ross wrote: "To question this (i. Alexander Ross (c 1590 - 1654 was a prolific Scottish writer and controversialist 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. This article is about the country of Egypt For a topic outline on this subject see List of basic Egypt topics. The Nile (النيل, Ancient Egyptian iteru or Ḥ'pī, Coptic piaro or phiaro) is a major north-flowing River "^[9]

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. Girolamo Fracastoro ( Fracastorius) (1478‑ August 8, 1553) was an Italian Physician, Scholar (in Mathematics Next, Robert Hooke published the first drawings of a microorganism in 1665. Robert Hooke, FRS (18 July 1635 – 3 March 1703 was an English Natural philosopher and Polymath who played an important role in the He is also credited for naming the cell which he discovered while observing cork samples.

Then in 1676 Anthony van Leeuwenhoek discovered microorganisms that, based on his drawings and descriptions are thought to have been protozoa and bacteria. Antonie Philips van Leeuwenhoek (October 24 1632 &ndash August 30 1723 was a Dutch tradesman and Scientist from Delft, the Netherlands Protozoa (in Greek πρῶτον proton "first" and ζῷα zoia "animals" are unicellular Eukaryotes (singular The Bacteria ( singular: bacterium) are a large group of unicellular Microorganisms Typically a few Micrometres in length bacteria have This sparked a renewal in interest in the microscopic world. ^[10]

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. Italy (Italia officially the Italian Republic, (Repubblica Italiana is located on the Italian Peninsula in Southern Europe, and on the two largest Francesco Redi (February 18/19 1626&ndash March 1, 1697) was an Italian Physician. Maggot is the common name of the Larval phase of development in insects of the order Diptera (flies 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, from an egg). Biogenesis is the process of Lifeforms producing other lifeforms e

In 1768 Lazzaro Spallanzani proved that microbes came from the air, and could be killed by boiling. Lazzaro Spallanzani ( January 10, 1729 - February 12, 1799) was an Italian Biologist whose research of Biogenesis A microorganism (also spelled micro organism or micro-organism and also called a microbe) is an Organism that is Microscopic (usually 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. Louis Pasteur (27 December 1822 – 28 September 1895 a French Chemist and Microbiologist, is best known for remarkable breakthroughs in the causes and Cell Theory refers to the idea that cells are the basic unit of structure in every living thing

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. Louis Pasteur (27 December 1822 – 28 September 1895 a French Chemist and Microbiologist, is best known for remarkable breakthroughs in the causes and Philosophical naturalism has been described in various ways In its broadest and strongest sense naturalism is the metaphysical position that "nature is all there is In a letter to Joseph Dalton Hooker on February 1, 1871,^[11] 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. Sir Joseph Dalton Hooker, OM, GCSI, MD, FRS (30 June 1817 – 10 December 1911 was an English Botanist and Explorer Events 1327 - Teenaged Edward III is crowned King of England, but the country is ruled by his mother Queen Year 1871 ( MDCCCLXXI) was a Common year starting on Sunday (link will display the full calendar of the Gregorian calendar (or a Common Charles Robert Darwin (February 12 1809 &ndash April 19 1882 was an English naturalist, who realised and demonstrated that all Species of life 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. "^[12] In other words, the presence of life itself makes the search for the origin of life dependent on the sterile conditions of the laboratory.

Haldane and 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. Alexander Ivanovich Oparin (Алекса́ндр Ива́нович Опарин ( Uglich, Russia &ndash April 21, 1980, Moscow In his The Origin of Life on Earth,^[13][14] 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 dissolved into a coacervate droplet. A coacervate is a tiny spherical droplet of assorted organic molecules (specifically Lipid molecules which is held together by Hydrophobic forces from a surrounding 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. The term cell growth is used in two different ways in Biology. Reproduction is the Biological process by which new individual Organisms are produced Metabolism is the set of Chemical reactions that occur in living Organisms in order to maintain Life. 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. John Burdon Sanderson Haldane FRS ( 5 November 1892 &ndash 1 December 1964) known as Jack (but who used 'J This idea was called biopoiesis or biopoesis, the process of living matter evolving from self-replicating but nonliving molecules. ^[15]

Early conditions

Morse and MacKenzie^[16] 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. The Hadean (ˈheɪdiən is the geologic eon before the Archean. Redox (shorthand for reduction-oxidation reaction describes all Chemical reactions in which atoms have their Oxidation number ( Oxidation state pH is the measure of the acidity or alkalinity of a Solution. 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. Zircon is a Mineral belonging to the group of nesosilicates. Its chemical name is Zirconium silicate and its corresponding chemical formula is Quartzite (from German Quarzit) not to be confused with the Mineral Quartz, is a hard Metamorphic rock which was originally The Narryer Gneiss Terrane is a geological complex in Western Australia that is composed of a tectonically interleaved and polydeformed mixture of Granite, mafic 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 continental crust is the layer of granitic, Sedimentary, and Metamorphic rocks which form the Continents and the areas of shallow seabed

Despite this, the Hadean environment was one highly hazardous to life. The Hadean (ˈheɪdiən is the geologic eon before the Archean. 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. ^[17]

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. The Late Heavy Bombardment (commonly referred to as the lunar cataclysm, or LHB) is a period of time approximately 3800 to 4100 million years ago ( mya 8 and 4. 1 billion years would likely have sterilised the planet if life had already evolved by that time.

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. ^[18]

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. Stanley Lloyd Miller ( March 7, 1930 - May 20, 2007) was an American Chemist and Biologist who is known Adenine is a Purine with a variety of roles in Biochemistry including Cellular respiration, in the form of both the energy-rich Adenosine Guanine is one of the five main Nucleobases found in the Nucleic acids DNA and RNA, the others being Adenine, Cytosine, Cytosine is one of the five main bases found in DNA and RNA. It is a Pyrimidine derivative with a Heterocyclic Aromatic ring Uracil is a common and naturally occurring Pyrimidine derivative ^[19] Based on his research he suggested a beginning of life involving freezing conditions and exploding meteorites. ^[20] 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. Discover is a Science magazine that publishes articles about Science for a general audience Ammonia is a compound with the formula N[[hydrogen H3]] It is normally encountered as a Gas with a characteristic pungent Odor A cyanide is any Chemical compound that contains the cyano group (C≡N which consists of a Carbon Atom triple-bonded to a ^[21] 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. ^[22] 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. ^[23]

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. 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 (Godthåb at. 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. ^[24] 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. A heterotrophs, or chemoorganotrophy ( Greek heterone = (another and trophe = nutrition is an Organism that requires Cyanobacteria, also known as blue-green algae, blue-green bacteria or Cyanophyta, is a phylum of Bacteria that obtain their energy ^[25]

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. In Chemistry, a molecule is defined as a sufficiently stable electrically neutral group of at least two Atoms in a definite arrangement held together by A monomer (from Greek mono "one" and meros "part" is a small Molecule that may become chemically bonded to other In Chemistry, an amino acid is a Molecule containing both Amine and Carboxyl Functional groups In Biochemistry, this This was demonstrated in the Miller-Urey experiment by Stanley L. Miller and Harold C. Urey in 1953. The Miller-Urey experiment (or Urey-Miller experiment) was an Experiment that simulated hypothetical conditions present on the Early Earth and tested Stanley Lloyd Miller ( March 7, 1930 - May 20, 2007) was an American Chemist and Biologist who is known Harold Clayton Urey ( April 29, 1893 &ndash January 5, 1981) was an American Physical chemist whose pioneering work
2. Phospholipids (of an appropriate length) can spontaneously form lipid bilayers, a basic component of the cell membrane. Phospholipids are a class of Lipids and are a major component of all Biological membranes All phospholipids contain a Diglyceride, a Phosphate A lipid bilayer or bilayer lipid membrane ( BLM) is a membrane composed of Lipid molecules (usually Phospholipids. The cell membrane (also called the plasma membrane, plasmalemma, or "phospholipid bilayer" is a Selectively permeable Lipid bilayer
3. The polymerization of nucleotides into random RNA molecules might have resulted in self-replicating ribozymes (RNA world hypothesis). A polymer is a large Molecule ( Macromolecule) composed of repeating Structural units typically connected by Covalent Chemical bonds Nucleotides are Organic compounds that consist of three joined structures a nitrogenous base a Sugar, and a Phosphate group Ribonucleic acid ( RNA) is a Nucleic acid that consists of a long chain of Nucleotide units A ribozyme (from ribo nucleic acid en' zyme', also called RNA Enzyme or catalytic RNA is an RNA Molecule that catalyzes The RNA world hypothesis proposes that a world filled with life based on Ribonucleic acid (RNA predated current life based on Deoxyribonucleic acid (DNA
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. In the context of Evolution, certain traits or Alleles of a Species may be subject to selection The Peptidyl transferase is an aminoacyltransferase ( and the primary Enzymatic function of the Ribosome which forms Peptide links between Thus the first ribosome is born, and protein synthesis becomes more prevalent. Ribosomes ( from ribo nucleic acid and "Greek soma ( meaning body") are complexes of RNA and Protein that
5. Proteins outcompete ribozymes in catalytic ability, and therefore become the dominant biopolymer. Proteins are large Organic compounds made of Amino acids arranged in a linear chain and joined together by Peptide bonds between the Carboxyl Nucleic acids are restricted to predominantly genomic use. Genomics is the study of an organism's entire Genome. The field includes intensive efforts to determine the entire DNA sequence of organisms and fine-scale Genetic

The origin of the basic biomolecules, while not settled, is less controversial than the significance and order of steps 2 and 3. A biomolecule is any organic Molecule that is produced by living Organisms including large Polymeric molecules such as Proteins The basic chemicals from which life is thought to have formed are:

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-). Methane is a Chemical compound with the molecular formula. It is the simplest Alkane, and the principal component of Natural gas. Ammonia is a compound with the formula N[[hydrogen H3]] It is normally encountered as a Gas with a characteristic pungent Odor Water is a common Chemical substance that is essential for the survival of all known forms of Life. Hydrogen sulfide (or hydrogen sulphide) is the Chemical compound with the formula H 2 S. Carbon dioxide ( Chemical formula:) is a Chemical compound composed of two Oxygen Atoms covalently bonded to a single Carbon monoxide, with the chemical formula CO is a colorless odorless tasteless yet highly toxic Gas. A phosphate, an Inorganic chemical, is a salt of Phosphoric acid.

Molecular oxygen (O₂) and ozone (O₃) were either rare or absent. Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the OZONE is an object oriented Operating system written in the C programming language.

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"). 2008 ( MMVIII) is the current year in accordance with the Gregorian calendar, a Leap year that started on Tuesday of the Common 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. Steen Rasmussen was born in Elsinore Denmark, in 1955 He is an Artificial Life scientist who has published numerous reviews and reports in the Journal Artificial Los Alamos National Laboratory (LANL (previously known at various times as Site Y, Los Alamos Laboratory, and Los Alamos Scientific Laboratory) is a Jack W Szostak (born November 9, 1952) is an American Biologist and Professor of Genetics at Harvard Medical School and Alexander 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. J Craig Venter (born John Craig Venter October 14, 1946, Salt Lake City Utah) is an American Biologist, and businessman The Institute for Genomic Research ( TIGR) was a Non-profit Genomics research institute founded in 1992 by Craig Venter in 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. John Desmond Bernal FRS (born 10 May 1901 died 15 September 1971 was an Irish-born scientist 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 Darwinian evolution may have commenced early, some time between Stage 1 and 2. A monomer (from Greek mono "one" and meros "part" is a small Molecule that may become chemically bonded to other A polymer is a large Molecule ( Macromolecule) composed of repeating Structural units typically connected by Covalent Chemical bonds eVolution is the third Album by eLDee, it was due to be released in 2008

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. Chondrites are stony Meteorites that have not been modified due to Melting or Differentiation of the parent body

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. ^[26]

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.

Miller's experiments (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 Miller-Urey experiment (or Urey-Miller experiment) was an Experiment that simulated hypothetical conditions present on the Early Earth and tested Stanley Lloyd Miller ( March 7, 1930 - May 20, 2007) was an American Chemist and Biologist who is known Harold Clayton Urey ( April 29, 1893 &ndash January 5, 1981) was an American Physical chemist whose pioneering work The " early Earth " is a term usually defined as Earth 's first billion years or gigayear. 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. The Miller-Urey experiment (or Urey-Miller experiment) was an Experiment that simulated hypothetical conditions present on the Early Earth and tested Methane is a Chemical compound with the molecular formula. It is the simplest Alkane, and the principal component of Natural gas. Ammonia is a compound with the formula N[[hydrogen H3]] It is normally encountered as a Gas with a characteristic pungent Odor Hydrogen (ˈhaɪdrədʒən is the Chemical element with Atomic number 1 A monomer (from Greek mono "one" and meros "part" is a small Molecule that may become chemically bonded to other Whether the mixture of gases used in the Miller-Urey experiment truly reflects the atmospheric content of early Earth is a controversial topic. The " early Earth " is a term usually defined as Earth 's first billion years or gigayear. 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 Oxygen Catastrophe was a massive environmental change believed to have happened during the Siderian period at the beginning of the Paleoproterozoic )

Simple organic molecules are, of course, a long way from a fully functional self-replicating life form. See also Biological reproduction Self-replication is any process by which a thing might make a copy of itself 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. A polymer is a large Molecule ( Macromolecule) composed of repeating Structural units typically connected by Covalent Chemical bonds Besides the necessary basic organic monomers, compounds that would have prohibited the formation of polymers were formed in high concentration during the experiments.

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. Hydrolysis is a Chemical reaction during which one or more water molecules are split into hydrogen and hydroxide ions which may go on to participate in further reactions Also, the Miller experiment produces many substances that would undergo cross-reactions with the amino acids or terminate the peptide chain.

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^[27]. Redox (shorthand for reduction-oxidation reaction describes all Chemical reactions in which atoms have their Oxidation number ( Oxidation state

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. Sidney Walter Fox ( 24 March 1912 - 10 August 1998) was a Los Angeles -born biochemist responsible for unique discoveries Peptides (from the Greek πεπτίδια, "small digestibles" are short Polymers formed from the linking in a defined order of α- Amino 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. This article largely refers to microspheres or protein protocells as small spherical units postulated by some scientists as a key stage in the Origin of life. ^[28]

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. Manfred Eigen ( May 9, 1927 -) is a German Biophysicist who won the 1967 Nobel Prize in Chemistry for work on measuring fast chemical reactions Peter K Schuster (born March 7, 1941) is a renowned biophysicist known for his work with the German Nobel Laureate Manfred Eigen in developing the The Max Planck Institute for Biophysical Chemistry ( Karl Friedrich Bonhoeffer Institute in Göttingen is a research institute of the Max Planck Society They examined the transient stages between the molecular chaos and a self-replicating hypercycle in a prebiotic soup. ^[29]

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. Information as a concept has a diversity of meanings from everyday usage to technical settings Ribonucleic acid ( RNA) is a Nucleic acid that consists of a long chain of Nucleotide units Enzymes are Biomolecules that catalyze ( ie increase the rates of Chemical reactions Almost all enzymes are Proteins Mathematically treated, hypercycles could create quasispecies, which through natural selection entered into a form of Darwinian evolution. The quasispecies model is a description of the process of the Darwinian Evolution of certain self-replicating entities within the framework of physical chemistry A boost to hypercycle theory was the discovery that RNA, in certain circumstances forms itself into ribozymes, capable of catalyzing their own chemical reactions. A ribozyme (from ribo nucleic acid en' zyme', also called RNA Enzyme or catalytic RNA is an RNA Molecule that catalyzes ^[30] 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.

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. The iron-sulfur world theory is a hypothesis for the Origin of life advanced by Günter Wächtershäuser, a Munich chemist and patent lawyer involving A black smoker or sea vent is 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 The iron-sulfur world theory is a hypothesis for the Origin of life advanced by Günter Wächtershäuser, a Munich chemist and patent lawyer involving 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.

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. The term sulfide ( sulphide in British English) refers to several types of Chemical compounds containing Sulfur in its lowest Oxidation Iron (ˈаɪɚn is a Chemical element with the symbol Fe (ferrum and Atomic number 26 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. Redox (shorthand for reduction-oxidation reaction describes all Chemical reactions in which atoms have their Oxidation number ( Oxidation state In Chemistry, an oligomer consists of a limited number of Monomer units (ολιγος or oligos is Greek for "a few" in contrast to a A polymer is a large Molecule ( Macromolecule) composed of repeating Structural units typically connected by Covalent Chemical bonds 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. An autocatalytic set is a collection of entities each of which can be created catalytically by other entities within the set such that as a whole the set is able to catalyze its own

The experiment produced a relatively small yield of dipeptides (0. A dipeptide is a molecule consisting of two Amino acids joined by a single Peptide bond. 4% to 12. 4%) and a smaller yield of tripeptides (0. A tripeptide is a Peptide consisting of three Amino acids joined by Peptide bonds Examples of tripeptides are Glutathione 10%) but the authors also noted that: "under these same conditions dipeptides hydrolysed rapidly. "^[31]

Radioactive beach theory

Zachary Adam^[32] 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. See Washington (disambiguation for other uses The University of Washington, founded in 1861, is a public research University Uranium (jʊˈreɪniəm is a silvery-gray Metallic Chemical element in the 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. Oklo is a region near the town of Franceville, in the Haut-Ogooué province of the Central African state of Gabon. Gabon (gəˈbɒn or /gaˈbõ/ in French) is a country in west central Africa sharing borders with Equatorial Guinea, Cameroon, Republic Such radioactive beach sand provides sufficient energy to generate organic molecules, such as amino acids and sugars from acetonitrile in water. In Chemistry, an amino acid is a Molecule containing both Amine and Carboxyl Functional groups In Biochemistry, this Sugar is a class of edible Crystalline substances mainly Sucrose, Lactose, and Fructose. Acetonitrile (ACN is the Chemical compound with formula CH3CN Radioactive monazite also releases soluble phosphate into regions between sand-grains, making it biologically "accessible". In Geology, the Mineral monazite is a reddish-brown Phosphate -containing rare earth metals and an important source of Thorium A phosphate, an Inorganic chemical, is a salt of Phosphoric acid. 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. History of the actinoid series From the earlier known chemical properties of actinium (89 up to uranium (92 indicating a relation to the Transition metals it was generally These complexes could have been important early catalysts to living processes. Catalysis is the process in which the rate of a Chemical reaction is increased by means of a Chemical substance known as a catalyst

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. The University of Aberdeen is an Ancient university founded in 1495, in Old Aberdeen, Scotland. Plate tectonics (from Greek τέκτων tektōn "builder" or "mason" describes the large scale motions of Earth 's Lithosphere As the early Earth is believed to have many smaller "platelets" it would provide a suitable environment for such processes.

Homochirality

Main article: Homochirality

Some process in chemical evolution must account for the origin of homochirality, i. 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. 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). In Chemistry, an amino acid is a Molecule containing both Amine and Carboxyl Functional groups In Biochemistry, this Ribose (ɹˈaɪbəʊs ɹˈaɪbəɹʊs primarily seen as D-ribose, is an Aldopentose — a Monosaccharide containing five Carbon Deoxyribose, also known as D-Deoxyribose and 2-deoxyribose, is an Aldopentose &mdash a Monosaccharide containing five Carbon Phospholipids are a class of Lipids and are a major component of all Biological membranes All phospholipids contain a Diglyceride, a Phosphate 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. In Chemistry, an enantiomer ( from the Greek ἐνάντιος opposite and μέρος part or portion is one of two Stereoisomers that are nonsuperimposable This is called a racemic mixture. In Chemistry, a racemic mixture, or racemate, is one that has equal amounts of left- and right-handed enantiomers of a chiral 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. The Murchison meteorite is named after Murchison Victoria, in Australia. It is suggested that polarised light has the power to destroy one enantiomer within the proto-planetary disk. Polarization ( ''Brit'' polarisation) is a property of Waves that describes the orientation of their oscillations In Chemistry, an enantiomer ( from the Greek ἐνάντιος opposite and μέρος part or portion is one of two Stereoisomers that are nonsuperimposable A protoplanetary disk (or proplyd) is a rotating Circumstellar disk of dense gas surrounding a young newly formed star a T Tauri star or Herbig star Noyes^[33] 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. In Nuclear physics, beta decay is a type of Radioactive decay in which a Beta particle (an Electron or a Positron) is emitted Leucine (abbreviated as Leu or L) is an α- Amino acid with the Chemical formula HO2CCH(NH2CH2CH(CH32 In Chemistry, a racemic mixture, or racemate, is one that has equal amounts of left- and right-handed enantiomers of a chiral Carbon-14, 14C, or radiocarbon, is a Radioactive isotope of Carbon discovered on February 27, 1940, by 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^[34]. Once established, chirality would be selected for. ^[35] 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^[36].

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. Self-organization is a process of Attraction and repulsion in which the internal organization of a System, normally an open system, increases 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. The cell membrane (also called the plasma membrane, plasmalemma, or "phospholipid bilayer" is a Selectively permeable Lipid bilayer Redox (shorthand for reduction-oxidation reaction describes all Chemical reactions in which atoms have their Oxidation number ( Oxidation state ^[37]

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"). History See also History of genetics The existence of genes was first suggested by Gregor Mendel (1822-1884 who in the 1860s studied inheritance Metabolism is the set of Chemical reactions that occur in living Organisms in order to maintain Life. Recently, trends are emerging to create hybrid models that combine aspects of both.

"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. The RNA world hypothesis proposes that a world filled with life based on Ribonucleic acid (RNA predated current life based on Deoxyribonucleic acid (DNA The RNA world hypothesis proposes that a world filled with life based on Ribonucleic acid (RNA predated current life based on Deoxyribonucleic acid (DNA Ribonucleic acid ( RNA) is a Nucleic acid that consists of a long chain of Nucleotide units 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. Proteinoids, or thermal proteins, are Protein -like molecules formed inorganically from Amino acids Some theories of Abiogenesis propose that Other possibilities include systems of chemical reactions taking place within clay substrates or on the surface of pyrite rocks. Clay is a naturally occurring material composed primarily of fine-grained Minerals which show plasticity through a variable range of Water content, and 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. A ribozyme (from ribo nucleic acid en' zyme', also called RNA Enzyme or catalytic RNA is an RNA Molecule that catalyzes Deoxyribonucleic acid ( DNA) is a Nucleic acid that contains the genetic instructions used in the development and functioning of all known Relatively short RNA molecules which can duplicate others have been artificially produced in the lab. ^[38]

Researchers have pointed out difficulties for the abiogenic synthesis of nucleotides from cytosine and uracil. Cytosine is one of the five main bases found in DNA and RNA. It is a Pyrimidine derivative with a Heterocyclic Aromatic ring Uracil is a common and naturally occurring Pyrimidine derivative ^[39] Cytosine has a half-life of 19 days at 100 °C and 17,000 years in freezing water. ^[40] Larralde et al, say that "the generally accepted prebiotic synthesis of ribose, the formose reaction, yields numerous sugars without any selectivity. "^[41] 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. ^[42]

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. A nucleic acid is a Macromolecule composed of chains of monomeric Nucleotides In Biochemistry these Molecules carry Genetic information Peptide nucleic acid (PNA is an artificially synthesized Polymer similar to DNA or RNA and is used in biological research and medical treatments Threose nucleic acid (TNA is a Polymer similar to DNA or RNA but differing in the composition of its "backbone" Glycerol nucleic acid (GNA is a Polymer similar to DNA or RNA but differing in the composition of its "backbone" ^[43][44]

"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. Year 1924 ( MCMXXIV) was a Leap year starting on Tuesday (link will display the full calendar of the Gregorian calendar. Alexander Ivanovich Oparin (Алекса́ндр Ива́нович Опарин ( Uglich, Russia &ndash April 21, 1980, Moscow A vesicle is a small bubble of liquid within a cell A more formal definition in Cell biology, would be that a vesicle is a relatively small intracellular membrane-enclosed 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. Günter Wächtershäuser, a Chemist turned patent lawyer, is mainly known for his groundbreaking and influential work on the Origin of life, and in particular The iron-sulfur world theory is a hypothesis for the Origin of life advanced by Günter Wächtershäuser, a Munich chemist and patent lawyer involving Christian René de Duve (born October 2, 1917) is an internationally acclaimed Cytologist and Biochemist. Thioesters are compounds resulting from the bonding of Sulfur with an Acyl group with the general formula R-S-CO-R'. 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. Freeman John Dyson FRS (born December 15, 1923) is an English-born American theoretical Physicist and Mathematician, famous for his Stuart Alan A Kauffman ( 28 September, 1939) is an American theoretical Biologist and Complex systems researcher concerning the Origin of An autocatalytic set is a collection of entities each of which can be created catalytically by other entities within the set such that as a whole the set is able to catalyze its own

However, the idea that a closed metabolic cycle, such as the reductive citric acid cycle, could form spontaneously (proposed by Günter Wächtershäuser) remains unsupported. The citric acid cycle, also known as the tricarboxylic acid cycle ( TCA cycle) or the Krebs cycle, (or rarely the Szent-Györgyi–Krebs cycle 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. Leslie Eleazer Orgel FRS ( January 12, 1927 &ndash October 27, 2007) was a British chemist In an article entitled "Self-Organizing Biochemical Cycles",^[45] 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. Acetyl-CoA is an important molecule in metabolism used in many biochemical reactions 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.

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. Evaporation is the process by which Molecules in a Liquid state (e 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. Amphiphile (from the Greek αμφις amphis both and φιλíα Philia: love friendship is a term describing a Chemical compound possessing both

Amphiphiles are oily compounds containing a hydrophilic head on one or both ends of a hydrophobic molecule. Hydrophile, from the Greek (hydros "water" and φιλια (philia "friendship" refers to a physical property of a Molecule In Chemistry, hydrophobicity (from the combining form of water in Attic Greek hydro- and for fear phobos) refers to the physical property of 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. Natural selection is the process by which favorable Heritable traits become more common in successive Generations of a Population of 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. The prokaryotes (proʊˈkærioʊts singular prokaryote /proʊˈkæriət/ are a group of Organisms that lack a Cell nucleus (= karyon or any other Animals Plants fungi, and Protists are eukaryotes (juːˈkærɪɒt or -oʊt Organisms whose cells are organized into complex ^[46]

Similarly, bubbles formed entirely out of protein-like molecules, called microspheres, will form spontaneously under the right conditions. This article largely refers to microspheres or protein protocells as small spherical units postulated by some scientists as a key stage in the Origin of life. 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). Protobionts are systems that are considered to have possibly been the precursors to Prokaryotic cells A protobiont is an aggregate of abiotically produced organic A micelle (rarely micella, plural micelles) is an aggregate of Surfactant molecules dispersed in a liquid Colloid. A coacervate is a tiny spherical droplet of assorted organic molecules (specifically Lipid molecules which is held together by Hydrophobic forces from a surrounding

A recent model by Fernando and Rowe^[47] 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. The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom, the UK or Britain,is a Sovereign state located Ethology ( from Greek ἦθος ethos, "character" and λόγος logos, "knowledge") is the scientific study of Animal Clinton Richard Dawkins, FRS, FRSL (born 26 March 1941 is a British ethologist, evolutionary biologist, and Popular science A single Chemical reaction is said to have undergone autocatalysis, or be autocatalytic, if the reaction product is itself the Catalyst for that reaction "MMIV" redirects here For the Modest Mouse album see " Baron von Bullshit Rides Again " The Ancestor's Tale (subtitled A Pilgrimage to the Dawn of Life) is a 2004 Popular science Book by Richard Dawkins 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). Julius Rebek Jr (born April 11, 1944) is a Hungarian -born American Chemist and expert on Molecular self-assembly. The Scripps Research Institute ( TSRI) is a Medical research facility that focuses on research in the basic Biomedical sciences Primarily located California ( is a US state on the West Coast of the United States, along the Pacific Ocean. 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. Natural selection is the process by which favorable Heritable traits become more common in successive Generations of a Population of

Clay theory

A model for the origin of life based on clay was forwarded by Dr A. Clay is a naturally occurring material composed primarily of fine-grained Minerals which show plasticity through a variable range of Water content, and Graham Cairns-Smith of the University of Glasgow in 1985 and adopted as a plausible illustration by several other scientists, including Richard Dawkins. Alexander Graham Cairns-Smith (born 1931 is an organic chemist and molecular biologist at the University of Glasgow, most famous for his controversial 1985 book Seven The University of Glasgow (Oilthigh Ghlaschu was founded in 1451 in Glasgow, Scotland and along with its contemporary institutions the University of St Andrews Year 1985 ( MCMLXXXV) was a Common year starting on Tuesday (link displays 1985 Gregorian calendar) Clinton Richard Dawkins, FRS, FRSL (born 26 March 1941 is a British ethologist, evolutionary biologist, and Popular science Clay theory postulates that complex organic molecules arose gradually on a pre-existing, non-organic replication platform — silicate crystals in solution. Alexander Graham Cairns-Smith (born 1931 is an organic chemist and molecular biologist at the University of Glasgow, most famous for his controversial 1985 book Seven 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". Exaptation, cooption, and preadaptation are related terms referring to shifts in the function of a trait during Evolution.

Cairns-Smith is a staunch critic of other models of chemical evolution. ^[48] 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. Potassium hydrogen phthalate, often called simply KHP, is a white or colorless ionic Solid that is the monopotassium salt of Phthalic acid "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". ^[49][50]

"Deep-hot biosphere" model of Gold

In the 1970s, Thomas Gold proposed the theory that life first developed not on the surface of the Earth, but several kilometers below the surface. Thomas Gold ( May 22, 1920 &ndash June 22, 2004) was an Austrian born Astrophysicist, a professor of Astronomy The discovery in the late 1990s of nanobes (filamental structures that are smaller than bacteria, but that may contain DNA in deep rocks) ^[51] might be seen as lending support to Gold's theory. Nanobes are tiny filamental Structures first found in some rocks and Sediments Some hypothesize that they are the smallest form of Life

It is now reasonably well established that microbial life is plentiful at shallow depths in the Earth (up to five kilometers below the surface)^[51] in the form of extremophile archaea, rather than the better-known eubacteria (which live in more accessible conditions). A microorganism (also spelled micro organism or micro-organism and also called a microbe) is an Organism that is Microscopic (usually The Bacteria ( singular: bacterium) are a large group of unicellular Microorganisms Typically a few Micrometres in length bacteria have 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. The Solar System consists of the Sun and those celestial objects bound to it by Gravity. Thomas Gold also asserted that a trickle of food from a deep, unreachable, source is needed for survival because life arising in a puddle of organic material is likely to consume all of its food and become extinct. Thomas Gold ( May 22, 1920 &ndash June 22, 2004) was an Austrian born Astrophysicist, a professor of Astronomy Gold's theory is that that flow of food is due to out-gassing of primordial methane from the Earth's mantle; more conventional explanations of the food supply of deep microbes (away from sedimentary carbon compounds) is that the organisms subsist on hydrogen released by an interaction between water and (reduced) iron compounds in rocks

"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). Methane is a Chemical compound with the molecular formula. It is the simplest Alkane, and the principal component of Natural gas. Microbial metabolism is the means by which a Microbe obtains the energy and nutrients (e (Note that exogenesis is related to, but not the same as, the notion of panspermia). Panspermia ( Gk. πάς/πάν (pas/pan all and σπέρμα ( sperma, seed is the Hypothesis that "seeds" of Life exist already A supporter of this theory was Francis Crick. Francis Harry Compton Crick OM FRS (8 June 1916 – 28 July 2004 Ph

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. Tar is a viscous black Liquid derived from the Destructive distillation of organic matter Ultraviolet ( UV) light is Electromagnetic radiation with a Wavelength shorter than that of Visible light, but longer than X-rays It is supposed that a rain of material from comets could have brought significant quantities of such complex organic molecules to Earth. A comet is a small Solar System body that orbits the Sun and when close enough to the Sun exhibits a visible coma (atmosphere or a tail —

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.

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. ^[52] Additional support comes from a recent discovery of a bacterial ecosytem whose energy source is radioactivity. ^[53]

A recent experiment led by Jason Dworkin, subjected a frozen mixture of water, methanol, ammonia and carbon monoxide to UV radiation, mimicking conditions found in an extraterrestrial environment. This combination yielded large numbers of organic material that self-organised to form bubbles when immersed in water. Dworkin considered these bubbles to resemble cell membranes that enclose and concentrate the chemistry of life, separating their interior from the outside world.

The bubbles produced in these experiments were between 10 to 40 micrometers, or about the size of red blood cells. Remarkably, the bubbles fluoresced, or glowed, when exposed to UV light. Absorbing UV and converting it into visible light in this way was considered one possible way of providing energy to a primitive cell. If such bubbles played a role in the origin of life, the fluorescence could have been a precursor to primitive photosynthesis. Such fluorescence also provides the benefit of acting as a sunscreen, diffusing any damage that otherwise would be inflicted by UV radiation. Such a protective function would have been vital for life on the early Earth, since the ozone layer, which blocks out the sun's most destructive UV rays, did not form until after photosynthetic life began to produce oxygen^[54].

Lipid World

There is a theory that ascribes the first self-replicating object to be lipid-like. ^[55] It is known that phospholipids form bilayers in water while under agitation– 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. Still, no biochemical mechanism has been offered to support the Lipid World theory.

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. ^[56][57] 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. Calcium phosphate is the name given to a family of Minerals containing Calcium Ions (Ca2+ together with orthophosphates (PO43-

PAH world hypothesis

Main article: PAH world hypothesis

Other sources of complex molecules have been postulated, including extraterrestrial stellar or interstellar origin. The PAH world hypothesis is a biological Hypothesis that proposes that the use of Polycyclic aromatic hydrocarbons (PAH was a means for a pre- RNA For example, from spectral analyses, organic molecules are known to be present in comets and meteorites. In 2004, a team detected traces of polycyclic aromatic hydrocarbons (PAH's) in a nebula. "MMIV" redirects here For the Modest Mouse album see " Baron von Bullshit Rides Again " A nebula (from Latin: "mist" pl nebulae or nebulæ, with ligature or nebulas) is an Interstellar cloud of ^[58] Those are the most complex molecules so far found in space. The use of PAH's has also been proposed as a precursor to the RNA world in the PAH world hypothesis. The PAH world hypothesis is a biological Hypothesis that proposes that the use of Polycyclic aromatic hydrocarbons (PAH was a means for a pre- RNA ^[59] The Spitzer Space Telescope has recently detected a star, HH 46-IR, which is forming by a process similar to the sun. The Spitzer Space Telescope (formerly the Space Infrared Telescope Facility, SIRTF) is an Infrared Space observatory. In the disk of material surrounding the star, there is a very large range of molecules, including cyanide compounds, hydrocarbons, and carbon monoxide. PAHs have also been found all over the surface of galaxy M81, which is 12 million light years away from the Earth, confirming their widespread distribution in space^[60].

Multiple genesis

Different forms of life may have appeared quasi-simultaneously in the early history of Earth. ^[61] The other forms may be extinct, leaving distinctive fossils through their different biochemistry (e. g. , using arsenic instead of phosphorus), survive as extremophiles, or simply be unnoticed through their being analogous to organisms of the current life tree. Alternative biochemistry is the speculative Biochemistry of alien Life forms that differ radically from those on Earth. An extremophile is an Organism that thrives in and may even require Physically or Geochemically extreme conditions that are detrimental to the Two structures in biology are said to be analogous if they perform the same or similar function by a similar mechanism but evolved separately Hartman^[62] for example combines a number of theories together, by proposing that:

The first organisms were self-replicating iron-rich clays which fixed carbon dioxide into oxalic and other dicarboxylic acids. This system of replicating clays and their metabolic phenotype then evolved into the sulfide rich region of the hotspring acquiring the ability to fix nitrogen. Finally phosphate was incorporated into the evolving system which allowed the synthesis of nucleotides and phospholipids. If biosynthesis recapitulates biopoesis, then the synthesis of amino acids preceded the synthesis of the purine and pyrimidine bases. Furthermore the polymerization of the amino acid thioesters into polypeptides preceded the directed polymerization of amino acid esters by polynucleotides.

See also

References

• Brooks, J; Shaw, G. Anatomy Commentary on Anatomy in Avicenna's Canon Astrochemistry is the study of the Chemical elements found in outer space generally on larger scales than the Solar System, particularly in molecular gas clouds Biogenesis is the process of Lifeforms producing other lifeforms e The Drake equation (also sometimes called the "Green Bank equation" the "Green Bank Formula" or often erroneously labeled the " Sagan equation" The history of Earth covers approximately 46 billion years (4567000000 years from Earth ’s formation out of the Solar nebula to the present Mimivirus is a viral genus containing a single identified species named Acanthamoeba polyphaga mimivirus (APMV Planetary habitability is the measure of a Planet 's or a Natural satellite 's potential to develop and sustain Life. In Planetary astronomy and Astrobiology, the Rare Earth hypothesis argues that the emergence of complex Multicellular life ( Metazoa A group of organisms is said to have common descent if they have a common Ancestor. Zeolites (Greek zein, "to boil" lithos, "a stone" are hydrated Aluminosilicate Minerals and have a micro-porous structure The question of the origin of water on Earth, or more accurately put the question of why there is clearly more Water on the Earth than on the other planets of the Solar The mediocrity principle is the notion in the Philosophy of science that there is nothing special about humans or the Earth Autocatalytic reactions are Chemical reactions in which at least one of the products is also a Reactant. (1973). Origins and Development of Living Systems. . Academic Press, 359. Academic Press ( London, New York and San Diego) was an Academic Book Publisher that is now part of Elsevier. ISBN 0-12-135740-6.  
• De Duve, Christian (Jan 1996). Christian René de Duve (born October 2, 1917) is an internationally acclaimed Cytologist and Biochemist. Vital Dust: The Origin and Evolution of Life on Earth. Basic Books. Basic Books is a book publisher founded in 1952. It publishes books in the fields of Psychology, Philosophy, Economics, Science, ISBN 0-465-09045-1.  
• Fernando CT, Rowe, J (2007). "Natural selection in chemical evolution. ". Journal of Theoretical Biology 247: 152–67. doi:10.1016/j.jtbi.2007.01.028. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.  
• Horgan, J (1991). "In the beginning". Scientific American 264: 100–109. Scientific American is a Popular science magazine, published (first weekly and later monthly since August 28, 1845, making it   (Cited on p. 108).
• Huber, C. and Wächterhäuser, G. , (1998). "Peptides by activation of amino acids with CO on (Ni,Fe)S surfaces: implications for the origin of life". Science 281: 670–672. Science is the Academic journal of the American Association for the Advancement of Science and is considered one of the world's most prestigious Scientific doi:10.1126/science.281.5377.670. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.   (Cited on p. 108).
• Martin, W. and Russell M. J. (2002). "On the origins of cells: a hypothesis for the evolutionary transitions from abiotic geochemistry to chemoautotrophic prokaryotes, and from prokaryotes to nucleated cells". Philosophical Transactions of the Royal Society: Biological sciences 358: 59–85. doi:10.1098/rstb.2002.1183. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.  
• Russell MJ, Hall AJ, Cairns-Smith AG, Braterman PS (1988). "Submarine hot springs and the origin of life". Nature 336: 117. doi:10.1038/336117a0. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.  
• Maynard Smith, John; Szathmary, Eors (2000-03-16). Maynard Smith redirects here -- for other uses see Maynard Smith (disambiguation Professor John Maynard Smith, F The Origins of Life: From the Birth of Life to the Origin of Language. Oxford Paperbacks. ISBN 0-19-286209-X.  
• Hazen, Robert M. (Dec 2005). Genesis: The Scientific Quest for Life's Origins. Joseph Henry Press. ISBN 0-309-09432-1.  
• Morowitz, Harold J. (1992) "Beginnings of Cellular Life: Metabolism Recapitulates Biogenesis". Yale University Press. ISBN 0-300-05483-1
• Dedicated issue of Philosophical Transactions B on Major Steps in Cell Evolution freely available.
• Dedicated issue of Philosophical Transactions B on the Emergence of Life on the Early Earth freely available.
• Luisi, Pier L. (2006). Emergence of Life: From Chemical Origins to Synthetic Biology. Cambridge University Press. ISBN 0-521-82117-7.  

Further reading

• Arrhenius, Gustaf; et al. (1997). "Entropy and Charge in Molecular Evolution—the Case of Phosphate". Journal of Theoretical Biology 187 (4): 503–522. doi:10.1006/jtbi.1996.0385. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.  
• Buehler, Lukas K. (2000–2005) The physico-chemical basis of life, http://www.whatislife.com/about.html accessed 27 October 2005. Events 312 - Constantine the Great is said to have received his famous Vision of the Cross. Year 2005 ( MMV) was a Common year starting on Saturday (link displays full calendar of the Gregorian calendar.
• Harris, Henry (2002). Things come to life. Spontaneous generation revisited. Oxford: Oxford University Press. ISBN 0198515383.  
• Hartman, Hyman (1998). "Photosynthesis and the Origin of Life". Origins of Life and Evolution of Biospheres 28 (4–6): 515–521. doi:10.1023/A:1006548904157. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.  
• Pitsch, Stefan; Krishnamurthy, Ramanarayanan; Arrhenius, Gustaf (2000). "Concentration of Simple Aldehydes by Sulfite-Containing Double-Layer Hydroxide Minerals: Implications for Biopoesis" (abstract). Helvetica Chimica Acta 83 (9): 2398 2411.  
• NASA Astrobiology Institute: Earth's Early Environment and Life
• NASA Specialized Center of Research and Training in Exobiology: Gustaf O. Arrhenius

Notes

External links

• Martin M Hanczyc and Jack W Szostak. Replicating vesicles as models of primitive cell growth and division. Current Opinion in Chemical Biology 2004, 8:660–664.PDF (192 KiB)
• "Exploring Life's Origins: a Virtual Exhibit"
• "SELF-REPLICATION: Even peptides do it" by Stuart A. Kauffman (web archive version as original page no longer accessible)
• Origins of Life website including papers, resources, by Dr. Michael Russell at the U. of Glasgow
• Possible Connections Between Interstellar Chemistry and the Origin of Life on the Earth
• Scientists Find Clues That Life Began in Deep Space—NASA Astrobiology Institute
• Self-organizing biochemical cycles—by Leslie Orgel
• How Life Began: New Research Suggests Simple Approach
• Primordial Soup's On: Scientists Repeat Evolution's Most Famous Experiment – an article in Scientific American. Events 1095 - The Council of Clermont, called by Pope Urban II to discuss sending the First Crusade to the Holy Land Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century. A kibibyte (a contraction of ki lo bi nary byte) is a unit of Information or Computer storage, established by the International Stuart Alan A Kauffman ( 28 September, 1939) is an American theoretical Biologist and Complex systems researcher concerning the Origin of March 28, 2007
• Illustrations from Evolution (textbook)