Re: Period of extinction

Hi

I think maybe your question got sent to the wrong guy!

By "global extinction", are you talking about extinction of animals or 
extinction of planets? 

I don't think anyone has tried to explain extinction of animals and plants
by referring to cosmic changes. The earth moves around the galactic center 
pretty slowly, and extinctions happen continuously.

There have been two pretty big biological extinction events, namely, when 
the dinosaurs were wiped out (and it's interesting to
think that a huge meteor might have caused that!) and the one which 
is going on right now and mainly has to do with people cutting down the 
rain forest in order to grow food in poor tropical countries. 
Probably the most kinds of different species that ever existed was 
about 50,000 to 10,000 years ago, before humans began having much impact
on the earth. Ever since the human population 
started to grow rapidly (that is, after agriculture was invented), the 
total numbers of different wild species have probably been declining).

If you are mainly interested in planets and extinction of planets then you 
should send your question again but reword it so that it gets sent to an 
astronomy guy instead of a biology guy! By the way there are a lot of 
interesting astronomy sites on the web. Try searching for "SETI" or NASA.

Good luck!

matt