[extropy-chat] Re: Animals

[Robert J. Bradbury]

On Wed, 18 Feb 2004, Christian Weisgerber wrote:

> Yes, but it's a slow, continuous process.  Anybody have any figures
> how much hotter the sun has grown over the time we've had multicellular
> life on earth?

Perhaps start here:
  http://directory.google.com/Top/Science/Astronomy/Stars/Stellar_Evolution/

Unfortunately
  http://en.wikipedia.org/wiki/Stellar_evolution
could use some work.

I suspect the number is probably ~10%.  But I would guess the key factor
would be the amount of CO2 in the atmosphere.  Early atmospheres probably
had much more CO2 producing a much greater greenhouse effect (most molecular
clouds are going to be rich in CO and CO2 due to supernovas that produce
these elements in large quantities).  The CO/CO2 gets incorporated into the
comets and the comets transfer the carbon to the planets.  Because life
needs carbon planets like Earth have been depleted of CO2 in the atmosphere
over time.  Venus and Mars just lucked out.  Venus is a little too close
to the Sun for life to develop while Mars doesn't quite have enough gravity to
retain an atmosphere in the long run.  Someplace out there there may be
a solar system where things got setup just right -- and it may have 3 Earths.

Robert