Super Novas' close enough to earth can sterlize it, but I think the life is extincted along with the ozone. Dr. Kieda touhed on that a little at our last meeting. Just of the top of my head, I'm just finishing dinner.
As I recall the extinctions come about 67 million years apart and most are believed to be caused by an Asteroid or Big Comet. A lot of these craters have been found, the Gulf of Mexico is approximately one of them. Geologist also point to the moon as evidence of many impacts in the last 4 billion years. The bad news is that it has been about 67 million years since our last extinction. I heard a biologist refer to Humans as a giant rock heading towards the earth. Which will get us first, ourselves or an Asteroid? Erik I read this article today on and thought it was interesting.
http://www.msnbc.msn.com/id/3900550/
Julie
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