Cradle of life or barren wasteland? Geochemical constraints on early martian water

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• Nick Tosca, University of Cambridge
• Tuesday 09 February 2010, 16:30-17:30
• Harker 1 seminar room, Department of Earth Sciences.

If you have a question about this talk, please contact John Maclennan.

From the moment surface expressions thought to result from the action of liquid water were first identified, the possibility that Mars may have hosted ancient or extant life has sparked a vigorous exploration program that has lasted for decades. Virtually every successful mission since the 1960’s has found evidence for water on Mars in one form or another. And, indeed, recent /in-situ/ and orbital exploration has shown that water undoubtedly left its mineralogical mark on the ancient martian surface. We now know (or think we know) that much of the action on Mars happened early – at ~4.2-3.5 Ga – before significant global-scale changes rendered the planet (or at least its surface) cold, dry, sterilizing and biologically foreboding. The result of such an evolutionary trajectory is the preservation of an unusual sedimentary record that was long ago obliterated on the Earth; a record that some think may shed light on the origin of life on Earth. But does water necessarily mean life? Collective geochemical and mineralogical observations now permit questions that go beyond the mere presence or absence of early martian water and address its chemistry and temporal footprint. These data tell the story of water’s limited persistence on the early martian surface. The discontinuous nature of wet intervals on early Mars, in turn, principally controlled local aqueous chemistry, periodically leading to salinity that would have challenged even the handful of microorganisms known to exhibit halo-tolerance on Earth through osmotic stress and loss of biopolymer functionality. But regardless of whether we accept this view of a persistently dry ancient Mars, even the most chemically benign surface environments must be viewed in planetary context; late heavy bombardment, early atmospheric loss and dynamo shutoff seem to have confined liquid water to a narrow window in time. Little is known about the boundaries of pre-biotic or early biologic environments, but compared to the watery origins of life on Earth the story of water on early Mars seems to have ended after the first chapter.

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This talk is part of the Department of Earth Sciences Seminars (downtown) series.

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