Precambrian Time

I have here what some imagine to be a sprawling Precambrian landscape. My lessons this year on the precambrian were influenced by Lynn Margulis's lecture on geomicrobiology and symbiogenesis at Woods Hole this summer. Make no mistake, a lot of stuff happened in the first several billion years of earth's history. Birdley books 8 and 9 will have comics on this. In our class we talked a good deal about all the wild events that occurred during this time, as well as how our friends the cyanobacteria set up earth's atmosphere to support the diversity of life we see today by filling it with oxygen. Thanks to them our atmosphere is around 20% oxygen, enough to support the diversity of life we see today. What some people don't know was that at the time of the "Oxygen Revolution," the influx of oxygen into the atmosphere killed off a lot of the obligate anaerobes - microbial species that required oxygen-free environments. Some fortunate ones survived by finding oxygen-free habitats like thermal vents. Another thing I learned is that before the cyanos filled the atmosphere with oxygen they sent all the oxygen into the oceans. It reacted with dissolved iron in the sea to form rust, which became locked up in geological features called banded iron formations (BIFs). So you can see how microbes were starting to shape the earth and its geological features. I say if you have a chance to teach about the Precambrian, spend some time on it. A lot of stuff happened over those several billion years.