Sunday, January 08, 2006

Old Times Now Forgotten

I have been reading about geology lately. Sometimes it's useful to remember how differently they did things back in the PreCambrian.

There wasn't any oxygen in the atmosphere back in the Archaean, at least not until 2.6 billion years or so ago. Hydrogen sulfide and methane were abundant in that strongly reducing atmosphere. Somewhere around that time, blue green algae evolved that began producing oxygen as a byproduct of their metabolism - most likely a byproduct that they, like the anaerobic bacteria with which they shared the planet at that time, found poisonous. Not to worry, though - there were abundant ions around to scarf up any stray oxygen. The banded iron formations that featured so prominently in the next 900 million or so years of Earth history were probably produced in just that way - dissolved iron ions scarfing up oxygen molecules and raining down on the sea floor as tiny specks of magnetite.

Global warming doubters like to argue that the human impact on the Earth is too small to really make a big difference, but geology is not entirely their friend in this debate. Life has been playing a major role in shaping the planetary atmosphere for billions of years, and there is little reason to believe that that has changed. Humans are now the final consumer for about 40-50% of all biological production on Earth and they have drastically altered the biosphere of every continent but Antarctica. It took the blue green algae as much as a couple of billion years to produce something like our current oxygen rich atmosphere. It looks like it will take us only about 50 more years (starting in 1850) to have doubled the CO2 in the atmosphere.