Mark Sturtevant Loc: Grand Blanc, MI

This is interesting, and its a fine part of a connected series of events that begins before the formation of the earth and solar system. The series is:
> Stars shine by atomic fusion, forming heavier atoms from lighter atoms. Its the more massive stars that can form elements heavier than helium. The more massive stars can make familiar elements like carbon, oxygen, nitrogen, silicone and so on. Up to iron. So there we have the elements needed to form rocky planets, water, and eventually carbon based life forms.
> The earth forms 4.5 billion years ago. The origin of life on earth is is detected in 3.8 billion year old sedimentary rocks. Maybe a bit earlier. All life depends on respiration to make ATP, and ATP is used for chemical energy in most of life's biochemistry. There are different kinds of respiration, but the first kinds cannot use oxygen b/c it is not abundant. Not yet...
> Not too long after, oxygenic photosynthesis begins. This is where oxygen gas (O2) is made as a waste product of photosynthesis. This is traced as mounting levels of iron oxides in sedimentary rocks. Microbes that find O2 to be toxic are gradually driven to low oxygen environments. If we detect a rich O2 atmosphere on an extrasolar planet, that will amount to proof of extraterrestrial life since no other process is known to produce high amounts of O2.
> With elevated O2, aerobic respiration that uses O2 is invented. This means large amounts of ATP can be made. Organisms can now be larger, more complex, and more active b/c of their abundant supplies of ATP.
> Another benefit of a high O2 atmosphere, is that some O2 is converted to O3 (ozone) high in the atmosphere. This is a good blocker of short wavelength UV light. It is because of ozone that life can evolve to live on land, out of the protective oceans.

StanMac Loc: Tennessee

Har de har har! Bad joke . . .

Stan

JBRIII

Recent work indicates that on worlds of mostly water, oxygen could accumulate without life by breakdown of water. H2 floats away into space leaving a high oxygen signature without life. Also, just yesterday a report indicated oxygen accumulated as the day got longer, apparently short days and nights not as good as long day and night for purple bacteria thought to be first to make oxygen.