From: henry@spsystems.net   
      
   In article <80d892ce.0309171334.69908b80@posting.google.com>,   
   Arduin  wrote:   
   >Presumably some amount of ejecta from the earth made its way to the   
   >moon, so would we be able to detect such materials from the earth?   
   >That is, at presumably very low concentrations, would our current   
   >technology allow us to determine the proportion of earth ejecta that   
   >has made its way to the moon?   
      
   Unfortunately, no.  Earth rocks and Moon rocks are not that different,   
   seen from a distance.   
      
   Folks have indeed suggested that you could find very old Earth rocks in   
   the lunar regolith... but the search would be difficult and tedious even   
   working on the lunar surface.   
      
   >As a follow-on question, if some of this ejecta made its way to the   
   >permanently shadowed south poles, would it be possible for rocks of   
   >sufficient size to shield the contents in the center from the energy   
   >of the ejection, the friction from the earth's atmosphere, and the   
   >impact upon the lunar surface?   
      
   As demonstrated by the Mars meteorites, the energy of ejection is not a   
   big issue.  (It used to be considered a prohibitive problem, but a closer   
   look says it's not so.)  The lunar impact is a bigger question mark, but   
   apparently there is reason to suspect that at least occasionally part of a   
   rock would survive.   
      
   >...But once at the south pole, the material   
   >should end up deeply frozen, I would expect.   
      
   Maybe.  It depends on the history of the Moon's axial tilt.  Current   
   thought is that Earth's high gravity and thick atmosphere permit ejection   
   of intact rocks only from very large impacts, which were largely confined   
   to the very early days of the solar system.  So such material would have   
   landed very early in the Moon's history.   
      
   Note also that there is considerable resurfacing of the Moon, even in the   
   polar regions, by smaller impacts.  The polar hydrogen deposits are   
   thought to be frozen gas from comparatively recent comet impacts.   
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