Atmospheric origin In the presence of iron in the bodies, some reduction reactions control the gases formed. Thus Carbon would be seen mainly as CO, N as N 2 , Hydrogen in H or H 2 form. In the absence of iron we would get chiefly H 2 O, CO 2 and N 2 . In addition to these considerations of the original components and reactions we also have to consider subsequent possible evolution of atmospheres - water can be extracted from the gas phase as ice and "locked in" to the body. Ultra-violet radiation can dissociate water to H 2 and O 2 , and the hydrogen flow outwards (hydrodynamic escape) can take other particles with it. (Thus, there is evidence of preferential loss on earth of lighter isotopes of Ne.) A relatively new theory from NASA suggests that regular increases in the amount of oxygen in the earth's atmosphere is caused by the loss of large amounts of organic matter in large-scale tectonic upheavals. An extra complication is the fact we must also take into account the sun's early history. It was,
This is the end of the preview. Sign up
access the rest of the document.