The lower bound for the longevity of an early ocean on Venus has been calculated to be about 600 My (Kasting, Icarus 1988). However, the inclusion of water clouds in recent models of an early wet Venusian atmosphere shows reduced solar forcing, resulting in oceans that could have lasted billions of years (Grinspoon and Bullock, BAAS 2003). If Venus did indeed have warm oceans for this long, it may well have been a crucible for the origin of life.Evidence for past oceans may be difficult to obtain, but there are a few promising avenues that, taken together, could provide substantial clues. One is the nature of the highlands crust. If rocks from these regions were produced from melts that had substantial interaction with an ocean, it is possible that they are andesitic or granitic. Mineralogical and petrographic information on the highlands crust will be crucial for making this determination. A second line of evidence involves the likely existence of hydrated minerals. Laboratory experiments have shown that the tremolite is metastable on Venus, decomposing on timescales of billions of years (Johnson and Fegley in Lunar and Planetary Science XXXI 2000) . Because of the large range of temperatures from lowlands to highlands on Venus ( 100 K), measurements of differential tremolite abundance can constrain the time a particular lithologic unit formed, the average surface temperature since its emplacement, or both. In situ X-ray diffraction analysis coupled with X-ray fluorescence spectroscopy on the surface of Venus can quantify the abundances of hydrated and other minerals with sufficient accuracy for these determinations. Finally, measurements of the isotopic ratios of hydrogen, carbon and oxygen in surface minerals and the atmosphere will help constrain how reservoirs of these elements have interacted over time, including the involvement of possible aqueous processes.
AAS/Division for Planetary Sciences Meeting Abstracts #39
- Pub Date:
- October 2007