Abstract Hoyle and Wickramasinghe have recently suggested that life may have originated in cometary nuclei rather than directly on Earth. Even though comets are known to contain substantial amounts of organic compounds which may have contributed to the formation of biochemical molecules on the primitive Earth, it is doubtful that the process of chemical evolution has proceeded in comets beyond the stage that has occurred in carbonaceous chondrites. Some of the arguments which do not favor the occurrence of biopoesis in comets are:A large layer of cometary ices is ablated from the nucleus' surface each time the comet passes through perihelion, so that essentially most of the organic products on the surface would be sublimed, blown off or polymerized.Because of the low temperatures of the cometary ices, polymers formed on one perihelion passage would not migrate deep enough into the nucleus to be preserved before they would be ablated away by the next perihelion passage.In the absence of atmosphere, and discrete liquid and solid surfaces, it is difficult to visualize the synthesis of key life molecules, such as oligopeptides, oligonucleotides and phospholipids by condensation and dehydration reactions as is presumed to have occurred in the evaporating ponds of the primitive Earth.Observations suggest that cometary nuclei have a rather weak structure. Hence, the low central pressures in comets combined with the high vapor pressures of cometary ices at the melting point of water ice, suggest that a liquid core is not a tenable structure. Yet, even if a cometary nucleus is compact enough to hold a liquid core and a transient liquid water environment was provided by the decay $ of^{26} $Al, the continuous irradiation in water of most of the biologically relevant polymers would have hydrolyzed and degraded them.Needless to say that the effects of radiation on self-replicating systems would also have caused the demise of any life forms which may have appeared under any circumstances.Concerning viruses, the high specificity of host-parasite relationships and their coevolutionary lines of descent, rule out a cometary origin for them. In summary, the view that life originated in comets is untenable in the light of all the available evidence.
Could life have evolved in cometary nuclei?
Origins of life ; 11 , 4
1981
Article (Journal)
English
Local classification TIB: | 535/3908/4290 | |
BKL: | 44.71 Verkehrsmedizin |
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