  We used chemical equilibrium calculations to model thermal outgassing of
ordinary chondritic material as a function of temperature, pressure, and bulk
compositions and use our results to discuss outgassing on asteroids and the
early Earth. The calculations include ~1,000 solids and gases of the elements
Al, C, Ca, Cl, Co, Cr, F, Fe, H, K, Mg, Mn, N, Na, Ni, O, P, S, Si, and Ti. The
major outgassed volatiles from ordinary chondritic material are CH4, H2, H2O,
N2, and NH3(the latter at conditions where hydrous minerals form). Contrary to
widely held assumptions, CO is never the major C-bearing gas during ordinary
chondrite metamorphism. The calculated oxygen fugacity (partial pressure) of
ordinary chondritic material is close to that of the quartz-fayalite-iron (QFI)
buffer. Our results are insensitive to variable total pressure, variable
volatile element abundances, and kinetic inhibition of C and N dissolution in
Fe metal. Our results predict that Earth's early atmosphere contained CH4, H2,
H2O, N2, and NH3; similar to that used in Miller-Urey synthesis of organic
compounds.
