Mathematics – Logic
Scientific paper
Apr 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003eaeja....10160r&link_type=abstract
EGS - AGU - EUG Joint Assembly, Abstracts from the meeting held in Nice, France, 6 - 11 April 2003, abstract #10160
Mathematics
Logic
Scientific paper
Mass-independent stable isotope fractionation (MIF), previously known in 16O/17O/18O in minerals from meteorites and in ozone from Earth atmosphere, has been discovered in surface sulfate (Bao et al. 2000, Nature 406, 176-178) and desert nitrate deposits (Michalski et al. 2000, EOS 81, F120). Sulfur isotope MIF has been discovered in Archean sulfide and sulfate minerals (Farquhar et al. 2000, Science). Anomalous fractionations in oxygen and sulfur isotopes originate during photochemical reactions induced by solar UV light in the atmosphere. These discoveries provide a new geochemical tool for studying the chemical evolution of the atmosphere. The modern and ancient records of MIF in both sulfur and oxygen isotopes differ considerably. It is proposed that these differences were caused by changes in the composition of the atmosphere, in particular, a major oxygenation event during the early Proterozoic. The modern geologic record shows that a large MIF in oxygen isotopes is transferred from stratospheric ozone via sulfate and nitrate aerosols and continuously deposited at Earth surface. Modern sulfur isotope anomalies are small and episodic in the stratigraphic record. Modern sulfur isotope MIF is carried by sulfate aerosols formed when giant volcanic eruptive clouds penetrate into the stratosphere. The known ancient record of oxygen isotope MIF extends only to the Miocene. The sulfur isotope record shows a sharp break in behavior at 2.3 Ga. Prior to that time and extending to rocks as old as 3.8 Ga, MIF CapDelta33S anomalies are more than 1 per mil and prevalent. After 2.3 Ga sulfur isotope MIF are less than 1 per mil. Atmospheric MIF sulfur isotope fractionations are modified at Earth surface by microbes which metabolize sulfur mass-dependently (MD). Microbial MD generates linear arrays of delta33S vs. delta34S with slope 0.5 and offset from the bulk Earth line. Examples of such linear arrays are known from rocks as old as 3.4 Ga.
Bekker Alexander
Farquhar James
Ono Satoshi
Pavlov Aleksei
Rumble Doug
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