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Hiromoto Nakazawa, National Institute for Materials Science (Japan)
Yoshihiro Furukawa, Tohoku University (Japan)
Shohei Ohara, Tohoku University (Japan)
Masahiro Oba, Tohoku University (Japan)
Takeshi Kakegawa, Tohoku University (Japan)
Toshimori Sekine, National Institute for Materials Science (Japan)
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Miller?fs experiment on the natural synthesis of organic molecules necessary for life?fs origin assuming atmospheric gases of H2, CH4, NH3 and H2O are known very widely. However, the geo-scientific research suggests the composition of the early atmosphere consisted of N2, H2O and CO/CO2 in which natural synthesis of organic molecules is difficult. Recent shock recovery experiments solved this inconsistency, i.e. heavy impacts of iron and carbon containing objects to early ocean might have produced wide variety of organic molecules including amino acid as well as ammonia even in N2, H2O and CO/CO2 atmosphere (Nakazawa et al, 2005; Furukawa et al, 2008).
Furthermore, a polymerization experiment of glycine has succeeded to form deca-oligopeptide without any catalyst under high pressure and dry conditions supposing an environment under deep sediments (Ohara et al, 2007).
These implicate a new scenario of the origin of life as that a mass of organic compounds had been prepared by reactions between components of extraterrestrial objects and the Earth, probably at 4.0∼3.8 Gyr ago. They had polymerized, organized, evolved to a life in deep sediments during diagenesis, and radiated adaptively in the ocean (Nakazawa, 2006; 2008).
During such evolution processes, there might have been natural selection mechanisms of pre-biotic molecules. The present paper explains it as follows: the heavy fall of the extraterrestrial objects containing metallic iron into the ocean would produce a reducing atmosphere thus generating a wide variety of organic molecules. Of these, only hydrophilic and clay-affinitive molecules could have survived the environment of strong UV radiation and oxidation, because they could be immersed in sea water and be adsorbed on clay particles that were finally deposited on the seabed. Their polymerization would be a further means of survival for the molecules when deposited in sediment that experienced dehydrating conditions of high-pressures and high-temperatures during diagenesis.
These polymers would then have had to survive hydrolysis through composite or cell formation. This may be the reason why almost all fundamental bio-organic molecules are hydrophilic and clay-affinitive. Thermodynamic background of the present explanation has been described elsewhere (Nakazawa, 2006; 2008).
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