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

[MEM]

I sit partially corrected: apparently the latest "oldest" is 4.404±.8 and it 
wasn't sandstone proper but metamorphosed sandstone which usually equates to 
quartzite.  The info did express there was some debate about a possible 
hydrothermal alteration of the zircons

This tightens the time lines substantially but the other comments 
remain valid until I find Where I am wrong again...lol  

Elton
<http://en.wikipedia.org/wiki/Oldest_dated_rocks>

Recent research
The zircons from the Western Australian Jack Hills returned an age of 4.404 
billion years, interpreted to be the age of crystallization.  These zircons also 

show another interesting feature; their oxygen  isotopic composition has been 
interpreted to indicate that more than 4.4  billion years ago there was already 
water on the surface of the Earth. The importance and accuracy of these 
interpretations is currently the subject of scientific debate. It may be that 
the oxygen isotopes, and other compositional features (the rare earth elements), 

record more recent hydrothermal alteration of the zircons rather than the 
composition of the magma at the time of their original crystallization. In a 
paper published in the journal Earth and Planetary Science Letters, a team of 
scientists suggest that rocky continents and liquid water existed at least 4.3 
billion years ago and were subjected to heavy weathering by an acrid climate. 
Using an ion microprobe to analyze isotope  ratios of the element lithium in 
zircons from the Jack Hills in Western  Australia, and comparing these chemical 
fingerprints to lithium  compositions in zircons from continental crust and 
primitive rocks  similar to the Earth's mantle, they found evidence that the 
young planet  already had the beginnings of continents, relatively cool 
temperatures  and liquid water by the time the Australian zircons formed.



----- Original Message ----
> From: MEM <mstreman53 at yahoo.com>
> To: Greg Catterton <star_wars_collector at yahoo.com>; 
>meteorite-list at meteoritecentral.com
> Sent: Sat, December 18, 2010 10:10:39 PM
> Subject: Re: [meteorite-list] Good read about the moon being captured by Earth
> 
> ----- 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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