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In contrast to the nebular-gas-cloud theory this theory held that Earth formed by accretion of small, cold bodies (dust and asteroids) (463, 1675). Stevenson (US), Takafumi Matsui (JP), and Yutaka Abe (JP) reasoned that the Earth with its metallic core, highly convective mantle, molten surface, and massive steam atmosphere, formed as a direct result of accretion (13, 1576, 2267). Pashley (AU) found membrane-forming non-polar molecules within the Murchison carbonaceous chondritic meteorite (696). Epps (US) reported the synthesis of phospholipids under primitive Earth conditions (1749). Kasting (US) showed that photochemistry in an atmosphere containing carbon dioxide or a mixture of carbon monoxide and carbon dioxide yielded formaldehyde as a major product (156, 1306, 1851). Exposure of the mixture to ultraviolet or visible light resulted in the direct synthesis of ATP (352). Deamer (US) found that fatty acids and glycerol combine spontaneously to produce phospholipids when heated to dryness at 65°C, as they might have been in an evaporating tide pool along a primitive sea (1070). Dworkin (US) and Juan Oró (US) synthesized uridine diphosphate glucose, cytidine diphosphate choline, other phosphorylated metabolic intermediates, the coenzymes adenosine diphosphate glucose (ADPG), guanosine diphosphate glucose (GDPG), and cytidine diphosphoethanolamine (CDP-ethanolamine) under primitive Earth conditions (1548, 1549). Woese (US), Francis Harry Compton Crick (GB), and Leslie Eleazer Orgel (GB-US) suggested that it would have been possible in a pre-DNA world to have a primitive replicating and catalytic apparatus devoid of both DNA and proteins and based solely on RNA molecules, i.e., an RNA world (556, 1744, 2639). This reaction demonstrates the feasibility of RNA-catalyzed RNA replications and supports the RNA world hypothesis (737).
Immanuel Kant (DE) had proposed much earlier that the Earth formed by condensation (1302, 1303). Williams (US) identified the oldest rocks found on Earth as granite-like rocks called gneiss from the Acasta Gneiss Complex near Great Slave Lake, Northwest Territory, Canada. The Isua Supracrustal rocks in West Greenland are a close second at 3.7 to 3.8 Ga. Kimball (US) synthesized adenine, thymine, amino acids, and other biochemical compounds from HCN in a primitive Earth environment (1746, 1747, 2264). Stanley Lloyd Miller (US), in Harold Clayton Urey’s (US) laboratory, showed that a wet mixture of methane, hydrogen, and ammonia exposed to electrical discharge for a while, formed traces of organic compounds, including organic acids and amino-acids regarded as exclusive components of living things (1629). Christopher Reid (GB), Leslie Eleazer Orgel (GB-US), and Cyril Ponnamperuma (LK-US) have shown that random processes can form nucleotides and dinucleotides. John Desmond Bernal (GB) proposed that one way in which organic subunits may spontaneously combine into larger molecules is by adsorption of the reacting molecules onto the highly ordered negatively charged aluminosilicates of clays. Walker () also proposed that under primitive Earth conditions organic polymers could have condensed on extremely thin layers of negatively charged aluminosilicates separated by layers of water (419). Joshi (US), and Juan Oró (US) produced polynucleotide polymers under primitive Earth conditions (2263). Bruce Michael Alberts (US), Walter Gilbert (US), and Antonio Lazcano (MX) proposed that DNA and proteins were derived from RNA-based cells or cell-like units (40, 962, 1409). De l'Hevrevx Accovchement des Femmes, ov il est Traicte du Gouuernement de leur Grossesse, de levr Travail Naturel et Contre Nature, du Traictement Estant Accouchees, et de leurs Maladies [The Happy Childbirth Women, or it is the Tract Governing their Pregnancy , their Labor Against Natural and Nature, the Document on Surviving Birth, and its Diseases].
Clair Cameron Patterson (US), George Tilton (US), and Mark Ingham (US) used uranium decay in rocks from Earth and in meteorites that struck Earth to date our solar system at 4.55 billion years old (1807-1809). These rocks were dated using the uranium 235 to lead 207 method (325). Master (US) synthesized amino acids from formaldehyde and hydroxylamine under primitive Earth conditions (1748). They have also demonstrated the formation of ATP through the ultimate agency of solar energy (1950). The clay surface performs a catalytic function (231, 232). Sidney Walter Fox (US), Kaoru Harada (JP), and Allen Vegotsky (US) showed how amino acids can be heated under Earth conditions to form proteinoids or "thermal proteins," which when placed in water self-organize into microspheres or protocells, possible precursors of the contemporary living cell (892-895). (US) and Juan Oró (US) synthesized peptides under plausible primitive Earth conditions (1095). Antonio Lazcano (MX) postulated that DNA evolved to replace RNA as the repository of hereditary information because, 1) DNA is much more resistant to harsh environmental conditions, 2) DNA is less prone to mutations which cannot be repaired, 3) cytosines in DNA are not as prone to spontaneously deaminate to uracil as they are in RNA, and 4) the duplex nature of DNA offered redundancy, which when coupled with repair mechanisms had a distinct advantage over simplex RNA without a repair mechanism (1410). Woese (US) originally described the progenote as the last common ancestor for archaebacteria (Archaea), eubacteria (Bacteria), and eukaryotes (Eucarya).
Alessandro Morbidelli (IT), John Chambers (US), Jonathan I. Pollack (US), and David Crisp (US) concluded that to keep the oceans from freezing on the primitive Earth a global "greenhouse" was necessary. Noam Lahav (IL), David White (US), and Sherwood Chang (US) experimentally produced peptide bonds under conditions where clay, water, and amino acids were subjected to cyclic variations in temperature and water content (1381). It contained informational polymers, could synthesize polypeptides, and was still evolving a link between genotype and phenotype (2640, 2641). Walter (US), speculated that life on Earth might have arisen as early as 3.9 Ga (2122). Hubbard (US) proposed how complex sequential metabolic pathways may have arisen as the result of selective pressure. Suppose that a contemporary cellular pathway makes a required substance such as an amino acid through the sequence A to B to C to D to E, in which A is a simple inorganic substance and E is the final organic product. Sur les anthérozoides et la double copulation sexuelle chez les végétaux angiospermes [On antherozoids and the double sexual copulation in angiosperm plants].
Lunine (US), Jean-Marc Petit (IT), Francois Robert (FR), Giovanni B. Cyr (US) proposed that as the solar system formed, Jupiter's powerful gravity perturbed asteroids to accrete into larger and larger objects resulting in terrestrial "embyros" near the size of Mars. Towe (US), Edward Anders (US), Gustaf Olaf Arrhenius (SE-US), Bibhas Ranjan De (US), Hannes Olof Gosta Alfvén (SE-US), Anne Benlow (GB), Arthur Jack Meadows (GB), Manfred A. Ahrens (US) proposed that on the primitive Earth, impact accretions from extraterrestrial objects represented a significant source of atmospheric and biogenic elements (75, 113, 223, 233, 697, 1393, 1927, 2309, 2366). This "greenhouse" would have offset the effects of a faint young Sun which was dimmer than today’s by 25-30%. Grotzinger (US) used greenhouse calculations and the sedimentary record to suggest that prior to 3.8 Ga the Earth’s surface was a warm (80-100˚C), with a bicarbonate-rich ocean at a p H perhaps as low as 6 (1020, 1307, 1484). Francis Harry Compton Crick (GB), Sydney Brenner (ZA-GB), Aaron Klug (ZA-GB), and George Pieczenik (US) proposed that the assignment of codons to particular amino acids was simply an historical accident. Initially E was plentiful in the environment and was absorbed directly by primitive aggregates.