Origins 2011 – Abstracts
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O3a: Contributed Orals – Early Earth processes
Early plate tectonics, pyrophosphate, Na+, and the origin of life
1Stockholm University, Sweden; 2Stockholm University, Sweden
Life may have started with plate tectonic processes. They started after the Hadean 4 Ga. The salinity of the young ocean was high. Hydrothermalism lead to serpentinization of olivine coupled to the formation of source molecules like H2. An environment in which Na+ exists is alkaline subduction zones, like the Mariana forearc. Pyrophosphate could have been formed during subduction by dehydration of protonated phosphates. The key to pyrophosphate formation is low water to rock ratio.
Hadean to Early Archean Impacts on Earth
Natural History Museum, Austria
Impact processes have been important for the Earth since its formation and early history. The first impact evidence on Earth are spherule layers in South Africa and Australia, 3.4 to 1.9 Gyr old. Geochemical studies are used to document old impacts. Our W isotope composition of known impactites gave a null result, which casts doubt on the earlier W isotopic evidence for a late heavy bombardment. Thus no good geochemical data exist so far for the late Hadean to early Archean impact history of the Earth.
Multiple sulfur and carbon isotope composition of the 2.7 Ga Manjeri and Cheshire Formations (Belingwe Greenstone Belt, Zimbabwe): a window on the Archean ocean “oxygenation”.
1UMR-CNRS Biogéosciences, France; 2Institut für Geologie und Paläontologie, Westfälische Wilhelms-Universität Münster, Germany; 3Department of Geology, Royal Holloway, University of London, Egham, Surrey TW200EX, UK
In order to bring insights into the biogeochemical conditions prevailing during the Mesoarchean attenuated MIF-S, we report the results of a carbon and multiple sulfur isotopic study through the ~2.7Ga Ngezi Group. Low δ13Corg values recorded in the Cheshire Fm. suggest a strong influence of methanotrphy, while the negative MIF-S signatures together with negative δ34S values in the Manjeri Fm. support the operation of bacterial sulfate reduction using atmospheric oxidize sulfur species.