See map of the world (link). It looks as if the amazon and
congo were created by an impact with a biological comet. It
also looks as if all the continent shapes are a splash effect
of the impact. Going with this theory, the great extinctions
could be orgasm
shudders -- each wave flinging
off a biological comet at a
singularity point, when complexity reaches a certain point of
maturity and the earth can't contain it anymore.
At this singularity people could roll tangles of
plants and other biological material into cords and knots
and create giant wings and the whole
network could lift off the planet.
The purpose of the biological comet could be to get the
complexity and heavy elements off the planet and to take
them somewhere else.
And monkeys could fly out of my ass tomorrow.
See link for speculation about Gamma ray bursts
being associated with extinctions.