Abiogenesis (/ˌeɪbaɪ.ɵˈdʒɛnɨsɪs/ ay-by-oh-jen-ə-siss[1]) or biopoiesis[2] is the natural process of life arising from non-living matter such as simple organic compounds.[3][4][5][6] The Earth was formed about 4.54 billion years ago. The earliest life on Earth existed at least 3.5 billion years ago,[7][8][9] during the Eoarchean Era when sufficient crust had solidified following the molten Hadean Eon. The earliest physical evidence for life on Earth is biogenic graphite in 3.7 billion-year-old metasedimentary rocks discovered in Western Greenland[10] and microbial mat fossils found in 3.48 billion-year-old sandstone discovered in Western Australia.[11][12] Nevertheless, several studies suggest that life on Earth may have started even earlier,[13] as early as 4.25 billion years ago according to one study,[14] and 4.4 billion years ago according to another study.[15] Earth is the only place in the universe known to harbor life.[16][17] Nonetheless, the exact steps in the abiogenesis process, whether occurring on Earth or elsewhere, remain unknown. Scientific hypotheses about the origins of life can be divided into three main stages: the geophysical, the chemical and the biological.[18] Many approaches investigate how self-replicating molecules or their components came into existence. On the assumption that life originated spontaneously on Earth, the Miller–Urey experiment and similar experiments demonstrated that most amino acids, basic chemicals of life, can be racemically synthesized in conditions which were intended to be similar to those of the early Earth. Several mechanisms have been investigated, including lightning and radiation. Other approaches (metabolism first hypotheses) focus on understanding how catalysi
Posted on: Sat, 26 Jul 2014 18:02:03 +0000