Mathematics – Logic
Scientific paper
Dec 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agufm.t41h..01j&link_type=abstract
American Geophysical Union, Fall Meeting 2004, abstract #T41H-01
Mathematics
Logic
8125 Evolution Of The Earth
Scientific paper
Isotopic (stable and radiogenic), as well as highly reduced characteristics indicate that EH (iron rich enstatite) chondrites, are the most likely building material for the Earth-Moon system.(Javoy 1995) Each new isotopic study in the recent years has reinforced that conclusion. The mineralogical and chemical composition of this Earth building material introduces several fundamental changes relative to the routinely and imprecisely named "chondritic composition" used up to now to describe the energetics of the Earth. This material is silicon and iron-rich, and much poorer in the main refractory radioactive elements (U, Th) than generally thought. This results in a distinctly different composition of the upper and lower mantle. The upper mantle keeps the general characteristics described previously while the lower mantle is richer in silicon and iron. The lower mantle mineralogy is essentially that of a Mg-Fe perovskite, denser by a few percent than the upper mantle material under identical P-T conditions. The core contains 7 to 9 % Si, 3 to 4 % O and little if any S. The oxidized iron distribution between upper and lower mantle and the core was established during the first 30 to 40 million years of the Earth history through the reaction : SiO2 +3 Fe = FeSi +2 FeO The radioactive content of the lower mantle has been almost 50% lower than that of the upper mantle during the first 2.5 billion years of the Earth's history. This enables the early setting of a stable two-level convection system in the mantle whose behaviour has been modeled successfully. The fine tuning of the Earth global composition around the average EH composition now awaits only improvements in high resolution geophysical data on the lower mantle. Javoy M. Geophys. Res. Let. 2219-2222, 1995.
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