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Project Progress

Environmental Conditions of Early Earth (dm)

This year our research focused on the climatic temperature of the early Earth at the time of the oldest microfossil record. Oxygen isotope data for the complete spectrum of cherts in the 3.5Ga Swaziland Sequence of South Africa were examined in terms of the sedimentologic and structural context . We were able to show that the oxygen isotopic composition of many of these cherts was clearly set during the early burial history in the Archean and were not “re-set” later as so many have casually asserted. The data indicate that climatic temperatures were drastically warmer than those of today and must have been in the range of 55°-80°C. Early life on Earth was a high-temperature affair, consistent with the thermophilic nature of the earliest organisms in the universal rRNA tree of life. Early high temperature life was not restricted to vent areas.

In response to the announcement of apparently recent aqueous seeps on Mars, this past year we deviated from the original research goals to develop an argument that these seeps, if aqueous, must be brines with freezing points lower than â??55°C. In reviewing current ideas about martian history, it is clear that if 1) Mars outgassed a hydrosphere, 2) lost most of its water via photodissociation/gravitation escape, and 3) subsequently froze, then eutectic brines should be present in the present martian subsurface.

In response to the heavy emphasis given to the “Snowball Earth” scenario at the 2000 NAI meeting, we also diverted from original plans to critically evaluate claims that the oxygen isotope composition of Neoproterozoic carbonates was “re-set” and should be ignored and also the extraordinary claims that carbon isotope “excursions” are global indicators of massive death of the biosphere. We analyzed new stratigraphic sections of the Beck Spring Dolomite in the Death Valley region of California and showed that oxygen and carbon isotope variations are correlative and that the “excursions” are actually local diagenetic events related to subaerial exposure of the carbonate.