HR: 0800h
AN: P41A-0214    [Abstracts]
TI: Chemistry of Earth's Putative Steam Atmosphere
AU: Fegley, B
EM: bfegley@wustl.edu
AF: Planetary Chemistry Laboratory Department of Earth and Planetary Sciences Washington University, One Brookings Dr., St. Louis, MO 63130, United States
AU: * Schaefer, L
EM: laura_s@wustl.edu
AF: Planetary Chemistry Laboratory Department of Earth and Planetary Sciences Washington University, One Brookings Dr., St. Louis, MO 63130, United States
AB: The concept of a steam atmosphere generated by impact devolatilization of planetesimals accreted during Earth's formation is over 20 years old (Matsui and Abe, 1986; Lange and Ahrens, 1982). Surprisingly, with the possible exception of a few qualitative remarks, no one has critically assessed this scenario. We use thermochemical equilibrium and, where relevant, thermochemical kinetic calculations to model the chemistry of the "steam" atmosphere produced by impact volatilization of different types of accreting material. We present results for our nominal conditions (1500 K, total P = 100 bar). We also studied the effects of variable temperature and total pressure. The composition of the accreting material is modeled using average compositions of the Orgueil CI chondrite, the Murchison CM2 chondrite, the Allende CV3 chondrite, average ordinary (H, L, LL) chondrites, and average enstatite (EH, EL) chondrites. The major gases released from CI and CM chondritic material are H₂O, CO₂, H₂, H₂S, CO, CH₄, and SO₂ in decreasing order of abundance. About 10% of the atmosphere is CO₂. The major gases released from CV chondritic material are CO₂, H₂O, CO, H₂, and SO₂ in decreasing order of abundance. About 20% of the total atmosphere is steam. The major gases released from average ordinary chondritic material are H₂, CO, H₂O, CO₂, CH₄, H₂S, and N₂ in decreasing order of abundance. The "steam" atmosphere is predominantly H₂ + CO with steam being about 10% of the total atmosphere. The major gases released from EH chondritic material are H₂, CO, H₂O, CO₂, N₂, and CH₄ in decreasing order of abundance. The "steam" atmosphere is predominantly H₂ + CO with about 10% of the total atmosphere as steam. This work was supported by the NASA Astrobiology and Origins Programs.
DE: 0325 Evolution of the atmosphere (1610, 8125)
DE: 5225 Early environment of Earth
DE: 5405 Atmospheres (0343, 1060)
DE: 5455 Origin and evolution
DE: 8125 Evolution of the Earth (0325)
SC: Planetary Sciences [P]
MN: 2007 Fall Meeting