Dan Dorritie has a free book, available on the web that amounts to a scientific thesis about the end of the great Permian extinction event, some 250 million years ago.
While is it scientific and rigorous, it is very readable. When I found it, I had lots of obligations I shamefully neglected in order to read it.
As I have stated, the major danger to our world today is the rapid liberation of huge quantities of methane from the continental shelves, particularly in the Arctic, and from the melting permafrost. So, the role of methane in the Permian extinction event, which killed perhaps 96% of all life of the time, is essential reading for anyone who wants to understand our world.
Bobbing Around 