From: John Clark (jonkc@worldnet.att.net)
Date: Thu Jun 28 2001 - 09:07:19 MDT
Eugene Leitl <Eugene.Leitl@lrz.uni-muenchen.de> Wrote:
> If the Moon orbit was low enough to melt Earth interior due to tidal
> forces, it wouldn't have taken long to bring it crashing on top of our
> heads.
Actually the opposite is happening, 2 billion years ago the moon was
about 4 times closer to the earth than it is now, and a day was about
half what it is now. Tidal forces from the moon have been slowing down
the Earth's rotation from the time that object was made, but angular
momentum is conserved and there is only one place that lost momentum
can go to, the moon's orbital velocity. The Moon is gradually accelerating
and so it's orbit is getting larger and it's moving away from us. This has to
be heating the Earth.
A secondary source of heat would come from radioactive isotopes that the
earth must have possessed in much higher abundance 4.6 billion years ago
than today. Radioactive potassium would have given off the most heat,
followed by uranium. Harold Urey calculated that the radioactivity alone was
enough to heat the center of the Earth to 1500 degrees C. The center of
the Earth is thought to be at about 5500 degrees C, the rest of the heat came
from tidal effects and more important, the kinetic energy of in-falling matter.
The Earth was formed by a very large cloud of particles, this cloud must have
possessed a lot of potential gravitational energy. When the Earth coalesced
this potential energy was gone but energy is conserved so it must be replaced
by heat energy, a LOT of heat energy, enough that if converted to kinetic energy
could push every atom in the planet away from the center at the escape velocity
of 7 miles a second.
John K Clark jonkc@att.net
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