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[bk090@freenet.carleton.ca (David Brez Carlisle)]

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.

David

--
>From: David Brez Carlisle
bk090@Freenet Carleton.CA