Not that I am really looking to rain on your parade, but on the topic of
plate tectonics, how would any one know if other earth-like planets have it
or not if they have never been there?  The other point that came to mind was
that with the billions and billions of stars and millions and millions of
galaxies out there, even a very small chance of a star system with a planet
capable of supporting life and a very small percentage of those planets
actually having life however complex would still come out to be a very, very
large number.  I think maybe this may be the modernization of the old 'The
Earth is the Center of the Universe' theory.

Curt Stafford
916 774-5126

-----Original Message-----
From: Tom Hula [mailto:[log in to unmask]]
Sent: Monday, May 08, 2000 6:47 AM
To: [log in to unmask]
Subject: OT: Rare Earth


Any opinions on the Rare Earth theory that seems to indicate that
complex animal life is quite rare in the Universe? I saw an article on
it at abc.com a while back and am now reading the book.

One of the areas covered is that there is likely a galactic habitable
zone. Brief summary:  not too close to the center of the galaxy where
the increased gamma rays and increased number of stars packed together
create an environment that would discourage the formation of complex
animal life. Then, further out at the periphery of the galaxy, they
claim that the resources needed to create a planet with a liquid metal
core simply don't exist. Also, we are in an area between spiral arms
where stars are scarce and so we have virtually no chance of being
affected by other stars going super nova. In other words, we appear to
be in an ideal locality and most stars are not. Also the Sun is a rare
star ... 95% of all stars are smaller with smaller habitable zones
around them. It has a life of 10 billion years, which would allow the
time needed for complex animal life to evolve.  Larger stars have too
short of a life-span.

There is much more, but I am struck by the fact that we live on a
special planet (only one with plate tectonics, for instance, which makes
it possible for us to live), orbiting in a stable manner around a
special star that is in just the right sort of place in the galaxy to
encourage complex animal life.  There is much more in the book of
course. I recommend Rare Earth highly, by Peter Ward and Donald
Brownlee, both from the University of Washington.

The thing that struck me the most: if complex life is such a rare thing
in the Universe, we must begin to treasure what we have here on Earth
while there is still something left to treasure.

--

        Tom Hula
        Victor S. Barnes Company
        616.361.7351  x173