Astrobiological Implications Of Differences In The Early Evolution Of The Terrestrial Planets (Earth, Mars, Venus)

Details Astrobiological Implications Of Differences In The Early Evolution Of The Terrestrial Planets (Earth, Mars, Venus) Astrobiological Implications Of Differences In The Early Evolution Of The Terrestrial Planets (Earth, Mars, Venus)

Dec 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufm.p22b0542w&link_type=abstract

American Geophysical Union, Fall Meeting 2001, abstract #P22B-0542

Mathematics

Logic

5499 General Or Miscellaneous

Scientific paper

The appearance of life on early Mars and Venus has been postulated on the grounds that the environmental conditions on these planets were similar. However, apart from the presence of water, an indigenous and exogenous source of organics, as well as various potential sources of energy (i.e. the vital ingredients for life), there are considerable differences in the early geological evolution of at least the Earth and Mars. This fact provokes the questions: How does this affect the possibility of the appearance of life on Mars? How can understanding of the geological context of early life on Earth aid the search for extraterrestrial life? There was liquid water on the surface of the Earth by 4.4 b.y. ago and the early Earth was essentially water-covered with an unknown quantity of mainly submerged protocontinents. Vertical movement dominated early tectonic processes with a transition to lateral tectonics in Early-Mid Archaean times, concomittant with the build up of rigid continental crust and a gradual decrease in mantle heat flow. Fossil remains from the E. Archaean Pilbara and Barberton greenstone belts point to the widespread formation of microbial matsby 3.5 b.y. in shallow water to subaerial environments strongly influenced by hydrothermal activity, on top of the protocontinents. Cratonisation during the Late Archaean/Palaeoproterozoic led to the creation of large continental platforms characterised by carbonate deposition and stromatolites. Gradual burial of organic carbon by tectonic processes, possibly coupled with biogenic oxygen production led to a build up of O2 in the atmosphere. Biological evolution (development of oxygenic photosynthesis and eukaryotes) was ultimately linked to this geological evolution. It is difficult to estimate the amount of water on the surface of early Venus. On the other hand, Mars was not water covered, did not have protocontinents, nor as active a tectonic regime as the Earth. If life did develop on that planet, it would initially have been restricted to specific, isolated habitats such as hydrothermal seeps in shallow water basins. The deteriorating conditions on the surface of Mars during the Late Noachian - Early Hesperion period may have stimulated a variety of environmental adaptations, which took longer to develop on Earth (e.g.psychrophily, xerophily). However, further evolution (e.g.oxygenic photosynthesis or eukaryotes) was probably inhibited.

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