The Great Oxidation Event

Today, mankind is changing the earth's atmosphere by adding large amounts of carbon dioxide to it. This is not the first time it's undergone massive changes, though.

A few billion years ago, the earth's atmosphere had very little free oxygen. Suddenly, about 2.4 billion years ago, a great amount of oxygen was almost instantaneously--in geological time--added to the mix. This was called the Great Oxidation Event.

The best theory available until this paper appeared in Nature (popular explanation here) was that oxidation "just happened" as photosynthesizing bacteria evolved, and free oxygen in the atmosphere went from its equilibrium value of a couple of percent to the approximately 18% it is today (with fluctuations along the way).

The problem is that the appearance of these bacteria predate the Great Oxidation Event by a few hundred million years. Why didn't the GOE happen earlier? What was keeping the oxygen at a low level for so long?

It turns out that the oxygen was counterbalanced by methane in the atmosphere. Methane is natural gas, the kind that powers your stove and lets you light your farts. Add methane and oxygen and you get carbon dioxide, water and heat. There was a lot of methane in the early atmosphere, most of it produced not by cows or consumption of Skyline chili, but by "methanogenic organisms": bacteria and the like that produce methane like we exhale carbon dioxide.

It turns out that these "methanogens" need nickel to survive. When they ran out of available nickel, due to changes in the earth's crust as it cooled and changed, they died back. The level of methane in the atmosphere gradually decreased and oxygen took over.

This is some really slick work which shows exactly how complex a system our ecology is.

What will the result be of dramatically increasing the carbon dioxide content in our atmosphere and oceans? We have some idea--massive warming and ocean acidification, among two--but there may be wholly unknown dangerous secondary effects from those primary effects. If ocean acidification results in a massive reduction of shelled creatures in the ocean, what will that do?

I'm not sure I want to find out by running the most massive atmospheric modification ever since the Great Oxidation Event.

1 comment:

Zack Morris said...

I talked with James Dobson, and he told me this all happened because of the methane fairies. So, you're full of crap. Sorry.