• [161] Subsequent research has shown possible routes of synthesis; for example, formamide produces all four ribonucleotides and other biological molecules when warmed in the
    presence of various terrestrial minerals.

  • [101] Nucleobases[edit] The majority of organic compounds introduced on Earth by interstellar dust particles have helped to form complex molecules, thanks to their peculiar
    surface-catalytic activities.

  • These molecules were not present on early Earth, but other amphiphilic long-chain molecules also form membranes.

  • Other approaches (“metabolism-first” hypotheses) focus on understanding how catalysis in chemical systems on the early Earth might have provided the precursor molecules necessary
    for self-replication.

  • [116] All four RNA-bases may be synthesized from formamide in high-energy density events like extraterrestrial impacts.

  • These could have provided the materials for DNA and RNA to form on the early Earth.

  • [154][156] RNA both expresses and maintains genetic information in modern organisms; and the chemical components of RNA are easily synthesized under the conditions that approximated
    the early Earth, which were very different from those that prevail today.

  • The prevailing scientific hypothesis is that the transition from non-living to living entities was not a single event, but an evolutionary process of increasing complexity
    that involved the formation of a habitable planet, the prebiotic synthesis of organic molecules, molecular self-replication, self-assembly, autocatalysis, and the emergence of cell membranes.

  • [40][41] Bernal said of the Miller–Urey experiment that “it is not enough to explain the formation of such molecules, what is necessary, is a physical-chemical explanation
    of the origins of these molecules that suggests the presence of suitable sources and sinks for free energy.

  • The RNA replication systems, which include two ribozymes that catalyze each other’s synthesis, showed a doubling time of the product of about one hour, and were subject to
    Darwinian natural selection under the experimental conditions.

  • During its formation, the Earth lost a significant part of its initial mass, and consequentially lacked the gravity to hold molecular hydrogen and the bulk of the original
    inert gases.

  • “[42] However, current scientific consensus describes the primitive atmosphere as weakly reducing or neutral,[43][44] diminishing the amount and variety of amino acids that
    could be produced.

  • Researchers generally think that current life descends from an RNA world, although other self-replicating molecules may have preceded RNA.

  • [5][6][11] The precursors to the development of a living cell like the LUCA are clear enough, if disputed in their details: a habitable world is formed with a supply of minerals
    and liquid water.

  • [20][36] J. D. Bernal showed that such mechanisms could form most of the necessary molecules for life from inorganic precursors.

  • Studies on vesicles from amphiphiles that might have existed in the prebiotic world have so far been limited to systems of one or two types of amphiphiles.

  • The main idea is that the molecular composition of the lipid bodies is a preliminary to information storage, and that evolution led to the appearance of polymers like RNA
    that store information.

  • A rain of material from comets could have brought such complex organic molecules to Earth.

  • [18] This theory held that “lower” animals were generated by decaying organic substances, and that life arose by chance.

  • The mechanism, now ubiquitous in living cells, powers energy conversion in micro-organisms and in the mitochondria of eukaryotes, making it a likely candidate for early life.

  • The advantage is that life is not required to have formed on each planet it occurs on, but rather in a more limited set of locations (potentially even a single location),
    and then spread about the galaxy to other star systems via cometary or meteorite impact.

  • [140][141][142] Multiple sources of energy were available for chemical reactions on the early Earth.

  • Besides the necessary basic organic monomers, compounds that would have prohibited the formation of polymers were also formed in high concentration during the Miller–Urey
    and Joan Oró experiments.

  • [84] Complex molecules, including organic molecules, form naturally both in space and on planets.

  • Carbon, currently the fourth most abundant chemical element in the universe (after hydrogen, helium and oxygen), was formed mainly in white dwarf stars, particularly those
    bigger than twice the mass of the sun.

  • The best of these would have favored the constitution of a hypercycle,[128][129] actually a positive feedback composed of two mutual catalysts represented by a membrane site
    and a specific compound trapped in the vesicle.

  • [45][46][47] Producing a habitable Earth Early universe with first stars[edit] See also: Chronology of the universe Soon after the Big Bang, which occurred roughly 14 Gya,
    the only chemical elements present in the universe were hydrogen, helium, and lithium, the three lightest atoms in the periodic table.

  • [55] The Hadean atmosphere has been characterized as a “gigantic, productive outdoor chemical laboratory,”[56] similar to volcanic gases today which still support some abiotic

  • In the first organisms, the gradient could have been provided by the difference in chemical composition between the flow from a hydrothermal vent and the surrounding seawater.

  • B. S. Haldane in 1929 proposed that the first molecules constituting the earliest cells slowly self-organized from a primordial soup.

  • The advent of polymers that could replicate, store genetic information, and exhibit properties subject to selection was, it suggested, most likely a critical step in the emergence
    of prebiotic chemical evolution.

  • Many approaches to abiogenesis investigate how self-replicating molecules, or their components, came into existence.

  • These bodies may expand by insertion of additional lipids, and may spontaneously split into two offspring of similar size and composition.

  • [88] Organic compounds are relatively common in space, formed by “factories of complex molecular synthesis” which occur in molecular clouds and circumstellar envelopes, and
    chemically evolve after reactions are initiated mostly by ionizing radiation.

  • [77] In other parts of the Isua supracrustal belt, graphite inclusions trapped within garnet crystals are connected to the other elements of life: oxygen, nitrogen, and possibly
    phosphorus in the form of phosphate, providing further evidence for life 3.7 Gya.

  • [85] Organic molecules on the early Earth could have had either terrestrial origins, with organic molecule synthesis driven by impact shocks or by other energy sources, such
    as ultraviolet light, redox coupling, or electrical discharges; or extraterrestrial origins (pseudo-panspermia), with organic molecules formed in interstellar dust clouds raining down on to the planet.

  • On 1 February 1871 Charles Darwin wrote about these publications to Joseph Hooker, and set out his own speculation, suggesting that the original spark of life may have begun
    in a “warm little pond, with all sorts of ammonia and phosphoric salts, light, heat, electricity, &c., present, that a proteine compound was chemically formed ready to undergo still more complex changes.”

  • The study of abiogenesis aims to determine how pre-life chemical reactions gave rise to life under conditions strikingly different from those on Earth today.

  • [108][109] Laboratory synthesis[edit] As early as the 1860s, experiments demonstrated that biologically relevant molecules can be produced from interaction of simple carbon
    sources with abundant inorganic catalysts.

  • [5][6] The challenge for abiogenesis (origin of life)[7][8][9] researchers is to explain how such a complex and tightly-interlinked system could develop by evolutionary steps,
    as at first sight all its parts are necessary to enable it to function.

  • [124] Producing suitable vesicles The lipid world theory postulates that the first self-replicating object was lipid-like.

  • Such site/compound pairs are transmissible to the daughter vesicles leading to the emergence of distinct lineages of vesicles, which would have allowed Darwinian natural selection.

  • [86][87] Observed extraterrestrial organic molecules[edit] See also: List of interstellar and circumstellar molecules and Pseudo-panspermia An organic compound is a chemical
    whose molecules contain carbon.

  • [162][163][153] If such conditions were present on early Earth, then natural selection would favor the proliferation of such autocatalytic sets, to which further functionalities
    could be added.

  • [135] Such micro-encapsulation would allow for metabolism within the membrane and the exchange of small molecules, while retaining large biomolecules inside.

  • [152] However, RNA-based life may not have been the first to exist.

  • [135] Competition for membrane molecules would favor stabilized membranes, suggesting a selective advantage for the evolution of cross-linked fatty acids and even the phospholipids
    of today.

  • 355 genes appear to be common to all life; their nature implies that the LUCA was anaerobic with the Wood–Ljungdahl pathway, deriving energy by chemiosmosis, and maintaining
    its hereditary material with DNA, the genetic code, and ribosomes.

  • [48] As these stars reached the end of their lifecycles, they ejected these heavier elements, among them carbon and oxygen, throughout the universe.

  • The addition of iron and carbonate minerals, present in early oceans, however produces a diverse array of amino acids.

  • [138][139] Producing biology Energy and entropy[edit] Life requires a loss of entropy, or disorder, when molecules organize themselves into living matter.

  • [151] Many researchers concur that an RNA world must have preceded the DNA-based life that now dominates.

  • [14][8][15][16] A successful theory of the origin of life must explain how all these chemicals came into being.

  • [35] Haldane suggested that the Earth’s prebiotic oceans consisted of a “hot dilute soup” in which organic compounds could have formed.

  • Therefore, a boundary is needed to separate life processes from non-living matter.

  • For example, this was probably important for carbon fixation.

  • The 2015 NASA strategy on the origin of life aimed to solve the puzzle by identifying interactions, intermediary structures and functions, energy sources, and environmental
    factors that contributed to the diversity, selection, and replication of evolvable macromolecular systems,[2] and mapping the chemical landscape of potential primordial informational polymers.

  • In biology, abiogenesis (from a-‘not’ + Greek bios ‘life’ + genesis ‘origin’) or the origin of life is the natural process by which life has arisen from non-living matter,
    such as simple organic compounds.

  • [68] Earliest evidence of life[edit] Main article: Earliest known life forms Life existed on Earth more than 3.5 Gya,[69][70][71] during the Eoarchean when sufficient crust
    had solidified following the molten Hadean.

  • The energy required to release strongly-bound ATP has its origin in protons that move across the membrane.

  • A genomics approach has sought to characterise the last universal common ancestor (LUCA) of modern organisms by identifying the genes shared by Archaea and Bacteria, members
    of the two major branches of life (where the Eukaryotes belong to the archaean branch in the two-domain system).

  • [49] According to the nebular hypothesis, the formation and evolution of the Solar System began 4.6 Gya with the gravitational collapse of a small part of a giant molecular

  • [123] The explanation given for the unusual speed of these reactions at such a low temperature is eutectic freezing, which crowds impurities in microscopic pockets of liquid
    within the ice, causing the molecules to collide more often.

  • Small RNAs can catalyze all the chemical groups and information transfers required for life.

  • [100] A star, HH 46-IR, resembling the sun early in its life, is surrounded by a disk of material which contains molecules including cyanide compounds, hydrocarbons, and carbon


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[‘1. The reactions are:
FeS + H2S → FeS2 + 2H+ + 2e−
FeS + H2S + CO2 → FeS2 + HCOOH
2. ^ The reactions are:
Reaction 1: Fayalite + water → magnetite + aqueous silica + hydrogen
3Fe2SiO4 + 2H2O → 2Fe3O4 + 3SiO2 + 2H2
Reaction 2: Forsterite + aqueous
silica → serpentine
3Mg2SiO4 + SiO2 + 4H2O → 2Mg3Si2O5(OH)4
Reaction 3: Forsterite + water → serpentine + brucite
2Mg2SiO4 + 3H2O → Mg3Si2O5(OH)4 + Mg(OH)2
Reaction 3 describes the hydration of olivine with water only to yield serpentine and Mg(OH)2
(brucite). Serpentine is stable at high pH in the presence of brucite like calcium silicate hydrate, (C-S-H) phases formed along with portlandite (Ca(OH)2) in hardened Portland cement paste after the hydration of belite (Ca2SiO4), the artificial calcium
equivalent of forsterite. Analogy of reaction 3 with belite hydration in ordinary Portland cement: Belite + water → C-S-H phase + portlandite
2 Ca2SiO4 + 4 H2O → 3 CaO · 2 SiO2 · 3 H2O + Ca(OH)2
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