For the past 500 million years the Earth
has been dominated by (complex) animal
life. But it was not always so. There is
good evidence that life has existed
for at least 3,400 million years and probably for
4,000 million years. But for
more than 80% of Earth history there were no animals
at all; they burst onto the
world stage in a spectacular evolutionary panoply of
new life forms known as the
Cambrian Explosion. We have been in what might be called
an "Age of Animals" ever
since. We have a sense that the beginning of animal
life on our planet was an
act of youthful exuberance. But the reality is
that the Age of Animals is like
a baby born to almost impossibly old parents, an aberration
near the end of life.
The Earth, as an abode for life, is in at best late middle
age, and probably in
old age. The Age of Animals is a last hurrah. And
just as there was a beginning,
so too there will be an end to the Age of Animals.
And many other ends as well.
In this talk I give predictions about how and when habitability
on Earth will end;
the implications of how habitable planets "die" will
then be used to re-examine
the Drake Equation.