L'exobiologie ou l'origine chimique de la vie
Résumé
By definition, exobiology includes the study of the origin, evolution and distribution of life in the universe, terrestrial life serving as a reference in our search for extraterrestrial life. On Earth, life emerged in water about 4 billion years ago with organised molecular systems capable of self-reproduction and also capable of evolution. It is generally agreed that its main ingredients were liquid water and organic molecules, i.e. skeletons of carbon atoms flanked by hydrogen, oxygen, nitrogen, sulfur and phosphorus atoms. Organic matter might have been formed in the primitive Earth's atmosphere or near hydrothermal vents. A large fraction of prebiotic organic molecules might have been brought by extraterrestrial meteoritic and cometary dust grains decelerated by the atmosphere. The possibility that life might have evolved on early Mars, when water existed on the surface, marks it as a prime candidate in the search for microbial life beyond the Earth. Europa has an icy carapace and probably a subsurface region of water which might harbor a basic life form. The atmosphere and surface components of Titan are also of interest to exobiology for the insight into a hydrocarbon-rich, chemically evolving world. Furthermore, the detection of interstellar organic molecules and the discovery of extrasolar planets broaden the field of astrobiology to the whole Universe.
Domaines
Autre
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