The origin of life

• Published in: Earth-science reviews 1999-07, Vol.47 (1), p.71-93
• Main Author: McClendon, John H
• Format: Article
• Language: English
• Subjects: Archean; atmosphere; Biochemistry; comets; Earth origin; Fossils; Geological time; Geology; Hadean; hydrothermal springs; Life; life origin; Microbiology; ocean; Paleontology; phylogeny; Precambrian
• ISSN: 0012-8252; 1872-6828
• DOI: 10.1016/S0012-8252(99)00015-X

Microfossil finds have been firmly established at about 3.5 Ga (giga annee=10 9 years), but no rocks older than about 4.0 Ga have been demonstrated, leaving the history of the first 0.6 Ga missing. This gap has been filled by models of the solar system. The origin of the ocean, atmosphere, and much crustal material apparently lies in a heavy rain of comets, subsequent to the catastrophic Moon-forming event. The earliest microfossils are those of the Apex chert in Australia, about 3.5 Ga old. `Prebiotic' simulations of possible biochemistry have made some progress in recent years, but many obstacles remain, and there is no agreement as to the course of development. The `ribose nucleic acid (RNA) World', aboriginal `clay genes', and catalysis on iron-sulfide precipitates are not ruled out. The search for the `last common ancestor' has reached a point between the Bacteria and the Archaea. It is possible that this organism may have been a thermophile, similar to many modern hot spring organisms. But it is likely to have been an autotroph, and a late development after the true origin of life. Even more speculative are suggestions about the origins of metabolic sequences, in particular the origin of the genetic code. Since all modern organisms share this code (and many other things), there had to be a long history of development during the blank period of Earth history.