2003 Seattle Annual Meeting (November 25, 2003)
Paper No. 26-7
Presentation Time: 8:00 AM-12:00 PM


ISOBE, Hiroshi, Department of Earth Sciences, Faculty of Science, Kumamoto Univ, Kumamoto, 860-8555, Japan, isobe@sci.kumamoto-u.ac.jp and IKEDA, Kurumi, Department of Systems in Natural Environment, Graduate School of Science and Technology, Kumamoto Univ, Kumamoto, 860-8555, Japan

The composition, conditions and evolution of the early atmosphere are one of the hottest arguments on history of the Earth. Degassing theory of the early atmosphere suggests that thick and hot atmosphere of H2O and CO2 covers magma ocean at the final stage of the Earth formation. Partial pressures of the H2O and CO2 would be 20MPa and 6MPa, respectively. This composition and pressure are very close to an azeotropic critical point of the H2O-CO2 system. Cooling of the hot H2O-CO2 atmosphere brings the first precipitation of liquid phase at above 300 degrees C. The first, hot rain of the Earth should be a supercritical acid rain. Interaction between the first rain and the primitive crust involves the early evolution of the atmosphere and the crust. In this study, we discuss evolution of the early atmosphere based on the results of the alteration experiments of minerals with the H2O-CO2 fluid. The H2O-CO2 fluid easily reacts with silicate minerals at around critical point of the fluid. A mass of CO2, which reacted with minerals to form carbonate minerals, can be measured by mass of the remaining CO2 gas in the capsule after each run. Consumption of CO2 increases up to approximately 40% and 80% at around 250 degrees C, for the mixture starting materials and olivine, respectively. The consumption of 80% of CO2 means that almost all Mg and Fe in the olivine starting material react with CO2. The Formation of carbonate minerals reduces the CO2 composition of fluid in the capsule to almost one fifth. The fixation of CO2 by carbonate formation should be very effective to reduce CO2 pressure from the early atmosphere in cooling through 250 degrees C. The first sediment of the primitive ocean should contain dolomite and hydrous silicate. The CO2 and H2O fixed in the first sediment should take an important role in the evolution of the early crust.

2003 Seattle Annual Meeting (November 25, 2003)
Session No. 26--Booth# 11
Planetary Geology (Posters)
Washington State Convention and Trade Center: Hall 4-F
8:00 AM-12:00 PM, Sunday, November 2, 2003

Geological Society of America Abstracts with Programs, Vol. 35, No. 6, September 2003, p. 22

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