Greetings,
The Earth capture theory creates a lot of problems due to the size of
the Earth/Moon system. I believe it is physically impossible. It has
long been discarded as a viable theory.
More likely an impact occured with the Earth during formation. At least
that is the most logical idea put forth so far.
I guess that bad ideas are defended until the death of the person that
generated the idea. Tektites also come to mind.
--AL Mitterling
Quoting MEM <[email protected]>:
----- Original Message ----
From: Greg Catterton
Subject: [meteorite-list] Good read about the moon being captured by Earth
about a year old but a good read and something to consider. I think this
theory is more plausible also.
Maybe the moon was hit and knocked towards Earth and was captured.
Yeah...BUT.....Capture theory doesn't address the identical oxygen isotope
ratios shared by Terra and Luna. Nor our 23° axis tilt. Nor the migration
dynamics to move .88 AU in 100 million years to be in place for the capture.
According to the article, Malcuit has been working on this for
several decades.
While Malcuit wasn't looking up from his desk, he may have missed the little
isotope-ratio "thingy".
While some rocks in Australia were dated to 4.0±.03 billion, the
claim for the
oldest earth rocks dated were in the range of 3.8-4.3 billion( a one half
billion error margin) leaving 400-500million years for the surface to
re-congeal--which the author doesn't think is adequate. The wack obviously
would have excavated some of the mantle but not necessarily the core.
I haven't
seen the math, so I don't know if the envelope of possibilities allow
for some
deep-crust plutons to have avoided being disrupted. Maybe we need to
be looking
for plutons with giant shattercones rather than micrometer-sized zircon
crystals. Another caveat in this "dating" is it isn't the rocks themselves
which are that old-- its the un-remelted zircons within them and a giant wack
would not necessarily have melted every last reservoir of zircon.
The zircons
in Australia were in much younger sandstone.
I'd like to know more about the mechanism of capture to convert a highly
elliptical orbit (which would be likely be passing inside the Roche radius of
the earth 16 times per year) into an almost circular one. ( I'd like to hear
more about the wack from the orbit from inside Mercury and how the Moon would
have retained so much silicate content which should have been boiled away).
While we know there is a small, permanent, tidal bulge, on the
backside of the
moon, the moon is far far less ellipsoid then predicted given the
perturbations
of the Roche limit would have exerted over part of the 3 billion years of
stabilizing--AND the moon would have to have been largely plastic-- if not
molten , for the ellipsoid to become spherical. BUT the moon is missing
compression ridges that would have been left by the tectonics a solid crust
floating on a plastic lunar mantel. I do agree that the churning would have
heated both earth and the moon if the moon had survived the capture for any
length of time--according to this theory. And we have calculated the rate the
moon is moving away from us such that 400mybp we had 20 hour days. So
where is
the orbital mechanics that got the moon so close and only to let it assume a
different orbital radius? The mechanism should have been a single vector not
first one than another.
I would also like to know what these "geologically impossibilities" are the
author did not elaborate on other than his argument on cooling rates and the
inferred "earliest age" the zircons could have formed that we use to date the
oldest rocks. This is the first I've heard that the" Big Wack" was
estimated
to have occurred after the earth had formed oceans.
Finally, some do believe there were a dozen or more bodies in the very early
solar system that were ejected out of the solar system else were
absorbed into a
body that yet remains. Calculations show that there are resonances and that
bodies have moved into orbits other than the ones they were formed in
but IIRC
these were largely inward migrations(?). What wacker "knocked" the
moon into a
radical orbit and where is the wacker today?
Seems someone has too much of their life invested in a theory
overcome by events
to accept that it is only a matter of time before the memorial
service. Thanks,
however, was a good read and I think we are open minded enough to weigh the
facts. Now if I can just get someone to agree with me about cold vs hot
meteorites...
Elton
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