[ExI] Fermi question, possible answer

John Clark johnkclark at gmail.com
Sat Apr 4 16:09:57 UTC 2015

On Sat, Apr 4, 2015 Tomaz Kristan <protokol2020 at gmail.com> wrote:

> What is known as the faint sun paradox - why was so warm on Earth back
> when our Sun was much fainter

Even more paradoxical is that 3 billion years ago on Mars, which is further
from that fainter sun than the Earth, it was warm enough for liquid water
to exist on it's surface. It's odd.

> > has a strange answer. Be cause our planet rotated faster!

Earth once rotated in less than 6 hours but back then the moon was much
closer and it's tidal forces slowed the rotation to 24 hours and is still
slowing it down; but angular momentum must be conserved so as the Earth
slows down the moon goes further away. Mars has no large moon to slow it
down and yet strangely it has almost the same rotational period as the
Earth. Coincidence I guess.

> > Yes, that's right. A faster rotating planet is warmer!

I have heard that global warming could increase the rotation of the Earth
because water expands when it gets warmer and water would tend to move from
the equator to the poles, but it's a very small effect, less than a
and the faster rotation is a effect of warming not a cause.

  John K Clark
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