Comentary impacts into ocean: thermochemical equilibrium calculations of high-temperature O 2 generation on the early earth

Abstract

The early Earth's atmosphere apparently differed from the present atmosphere mainly by its lack of free O 2 , a condition that is believed to have been indispensable for the origin of early anaerobic life forms. One of thecentral problems in Earth science is to explain the apparent transition from a primitive atmosphere (free of O 2 ) to the present atmosphere which holds 21 % of the gas. Theoretical models suggest that the initial form of O 2 in Earth's atmosphere may have been H 2 O, which was converted into atmospheric O 2 mainly through photosynthesis. I have investigated an alternative (abiotic) method for converting H 2 O to O 2 : a high temperature shock generated during the cometary impact into ocean (or on land). Calculations show that 1 % of the present atmospheric level (PAL) of O 2 could have resulted from an icy 29.2 km comet impacting the early (pre-oxygenic) Earth with a velocity between 18 and 37 km s - 1 . It is suggested that an abrupt supply (10 - 2 % of PAL) of free O 2 by the comet would be sufficient to make way for the appearance of oxygenic photosynthetic microorganisms.