AMMONIA PHOTOLYSIS AND THE GREENHOUSE EFFECT IN THE PRIMORDIAL ATMOSPHERE OF THE EARTH

Photochemical calculations indicate that in the prebiotic atmosphere of the Earth ammonia would have been irreversibly converted to N2 in less than 40 years if the ammonia surface mixing ratio were ≤ 10-4. However, if a continuous outgassing of ammonia were maintained, radiative equilibrium calculations indicate that a surface mixing ratio of ammonia of 10-5 or greater would provide a sufficient greenhouse effect to keep the surface temperature above freezing. With a 10-4 mixing ratio of ammonia, 60 to 70% of the present day solar luminosity would be adequate to maintain surface temperatures above freezing. A lower limit to the time constant for accumulation of an amount of nitrogen equivalent to the present day value is 10 my if the outgassing were such as to provide a continuous surface mixing ratio of ammonia ≥ 10-5. © 1979.