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Return to the fold
Hi! everyone! I can see again, after eye surgery. Now I have
the somewhat dubious pleasure o f reading almost 200 posts.
Someone enquired about the FIVE mass extinctions, I forget who.
A mass extinction is defined as any period of 1,000,000 years or
less in which more than ten percent of genera went extinct. (The
background level is 3 percent p er million years). On that basis
there were about 15 or 16 mass extinctions in the P hanerozoic.
The five biggest mass extinctions were:
Terminal Ordovician 435 Ma 50% genera 25% families
Late Devonian 357 60% 25%
Terminal Permian 248 80% 60%
Terminal Triassic 198 55% 25%
K-T 65 75% 50%
My book gives a fuller listing and graphical illustration of all 15.
That's enough for now - my vision is getting all fuzzy again.
>From: David Brez Carlisle