wrote:
blue.planet wrote:

Did the Moon siphon off much of the Earth's
atmosphere in earlier times.


No. Earth's gravity is substantially stronger than the moon's, so the
moon couldn't pull away atmosphere.

IIRC, oceans are pretty good about sucking up excess CO2.


Would being in the right orbit around the right sized star be
enough to creat the conditions for terrestrial type life, or is
a double planet like our Earth-Moon neccessary?


I don't think it's necessary, but it can help. At a minimum, a large
moon helps by minimizing random flips in a planet's tilt, which can
have drastic effects on the environment.

Mike Miller


That's right. Discovery Channel did a bit a few months ago called "If we
had no moon." It asserted that the presence of the moon makes a big
difference in the ability of the earth to support life. There's much
more to it than simply stabilizing the earth's spin; it also causes (or
at least, helps to cause) the tides, which keep the water of our oceans
moving around, which in turns helps promote sea life. It also tends to
sweep up meteorites that would otherwise hit the earth.

I must admit, I don't understand all I know about the stabilizing
effect. And my Ph.D. was in the dynamics of rotating bodies. I think
the issue has to do with the rotation of _FLEXIBLE_ bodies, rather than
rigid ones. Remember, the earth's crust is really a very thin thing
that floats on a liquid mantle. From fundamental physics, there is no
_WAY_ that the earth's angular momentum vector is going to change. It
precesses, because of luni-solar perturbations, at a slow rate (12,000
years per cycle) but it doesn't and can't change in magnitude.

But the earth's crust _CAN_ slip and slide around on the mantle. I
think maybe it's this that is stabilized by the moon, though I've not
found anyone who can explain the physics to me.

jack