Hi, Jerry, List,
The chief theorist about the origin of the Moon
was George Darwin (1845-1912, and the son of Charles
Darwin). His theory was that the Earth and Moon
fissioned under high initial rotation while still molten,
the Moon flying off into orbit and taking the angular
momentum with it, slowing the rotation of the Earth
(which it has and is still doing).
The day was shorter in past eras. In the Ordovician
(400 mya) there were about 400 days in a year. Two
studies of stromatolites show that at 700 mya, the year
was 435 days (a 20.1 hour day), and at 850 mya, the year
was 450 days (a 19.5 hour day).
The rate of change in the length of the day varies
because it is regulated by tidal friction which depends on
sea depths, coastlines, other changing geological features
and a lot of orbital details. But ultimately, for the theory
to work, the Moon's orbital velocity at the moment that
the Earth and Moon separate has to be the same as
the rotation rate of the Earth!
The orbital period of a satellite just above the
Earth's surface (assuming we had no atmosphere)
would be about 89 minutes. If the Earth was turning
this fast, the surface rock (or magma) would be
weightless, or very nearly. At this point a giant wave
or ripple could rise and detach itself from the
Earth, pulling up the material from which the
Moon would be made.
That's the physics of it, but George Darwin
was an astronomer as well as a physicist and knew
that the actual event would be messier: a lopsided
planet with a huge sticky lump on it. The lumpy
part above the Earth's surface would be orbiting
too fast and would apply a torque that would break
the Moon off (leaving the Pacific Ocean basin behind).
For almost a century, this was the major theory
of the origin of the Moon, its only rival being the
notion that the Moon was captured by the Earth's
gravity (which is a really hard trick, mathematically,
like juggling chains saws... running).
Remember, one of the reasons we had the Apollo
program was to discover the origin of the Moon.
Well, one of the scientific excuses, anyway. And
indeed, the moon rocks killed George's theory dead.
They were not Earth rocks of any conceivable kind.
I vividly recall a long article arguing for the Darwin
theory of the Moon's origin in the Journal of the British
Interplanetary Society (I was a student member) in
the late 1950's. It was full of equations and diagrams
and graphs, but it still seemed to me to be haunted
by improbability.
On the other hand, Harold Jeffrys in 1924 showed,
with a refined analysis of the tidal evolution of the Earth
and Moon, that the Earth could not be less than 4 billion
years old. In 1924, most geologists and physicists thought
the Earth was about 1.2 to 1.4 billion years old and it was
only 1947 when the first isotope date of 4.5 billion years
was measured.
The mathematical problem of calculating the change
in the rate of change in the length of the day was not
fully solved until 1994, so it took 120 years to work
out all the details!
Here's a fine piece on the history of the problem
of the tidal evolution of Earth and Moon on the internet:
http://www.talkorigins.org/faqs/moonrec.html
or just Google for Recession of the Moon.
As for the old Continental Drift and Other Dances,
Alfred Wegener gets all the credit for sticking to the
idea (even when it killed him, searching in Greenland
for evidence), but an American, F. B. Taylor, had
published a speculative paper suggesting continental
drift in 1910 which, however, had attracted little
attention, and neither had previous such suggestions
by Humbolt and Fisher.
Alfred Wegener (1880-1930) got all the attention
(if you want to call it that) for the idea of continental
drift. Here's some reviews of his 1912 book proposing it:
Utter, damned rot! said the president of the
American Philosophical Society.
If we are to believe [this] hypothesis, we must
forget everything we have learned in the last 70 years
and start all over again, said another American scientist.
Anyone who valued his reputation for scientific sanity
would never dare support such a theory, said a major
British geologist.
Clearly, it was a winner.
Wegener was also a meteorologist. He was the first
to describe the process (now called the Wegener-Bergeron-
Findeisen procedure) by which most raindrops form.
A good read on Wegener:
http://pangaea.org/wegener.htm
Sterling K. Webb
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- Original Message -
From: Gerald Flaherty [EMAIL PROTECTED]
To: Meteorite-list@meteoritecentral.com
Sent: Monday, January 29, 2007 3:30 PM
Subject: [meteorite-list] interesting speculation Pacific Basin origin
Just for fun, before we understood about plate tectonics
and thought that land only moved up and down, not back
and forth, it was widely believed that the Pacific Ocean was,
not an impact feature, but an outpact feature
