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Fwd: NASA/MARS Story

I originlly posted this on another list but similar questions have arisen on
this list as well. I also edited it slightly to hopefully pass through
Mickey's taphonomic filter ;-)

Forwarded message:
From:   Tompaleo@AOL.COM
Sender: owner-vrtpaleo@usc.edu
Reply-to:       vrtpaleo@usc.edu
To:     vrtpaleo@usc.edu
Date: 96-08-09 14:38:52 EDT

In a message dated 96-08-09 07:20:16 EDT, you write:

<< The Martian provenance of these meteorites is something I find more 
 curious.  If you believe the date given for the last bit of *in situ* 
 geology (3.6 billion years ago for the carbonates), how far can a piece of 
 rock travel in 3600  million years?  Is there evidence to suggest when 
 it was removed from it's original planet?  Let alone *which* planet...  
 Perhaps it was a bit of Precambrian Cambridge blown aloft for the odd eon
 before returning.

 From what I have read, the same K-Ar dating techniques used to date the
original provenance of the Martian material is used to date the time the
meteor(ite) was created. Just as the discussion of shocked quartz is integral
to the K-T and other terrestrial impacts, shocked glass inside the meteorite
is used to date the time of impact which created the meteorite in the first
place. It is called shock age. It is believed that when an impact occurs,
 some of the isotopic clock is reset and this reset time gives the age of the
meteorite. The non-shock component theoretically gives the age of the
original provenance . Thererfore in the case of this particular specimen, it
was blasted off of the Martian surface ca. 16Ma (the shock  age) ,  slowly
drifted inwards towards the sun for ~15 My   and was intercepted by the
earths gravitational field where it impacted 13Ka.

Thomas R. Lipka
Paleontological/Geological Studies