[meteorite-list] Good read about the moon being captured by Earth

[MEM]

----- 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