[meteorite-list] Ureilites/Venus

From: Steven Singletary <jumper_at_meteoritecentral.com>
Date: Thu Apr 22 09:49:01 2004
Message-ID: <200109181128.HAA19701_at_melbourne-city-street.mit.edu>

>
> Notwithstanding, isn't it possible that the material was blasted from
> Venus with a portion of the impactor early in Venuses history before
> "differentiation" occurred?



The next step would be to look at other systems to prove or disprove that.
When we look at the Sm-Nd systematics of ureilites, we find some of the
ureilites give Sm-Nd ages of 3.79 Ga. This is long after differentiation
occurred (and yet another puzzling aspect of the ureilites). If we take 4.56
Ga as the beginning of the solar system (in terms of accretion of all the
major
bodies) that gives almost 800 million years in which to mix and redistribute
the isotopes. 800 million years is more than enough time to do that when we
consider the process involved - heating from short lived radionuclides,
melting, mixing, etc. So the Ureilite parent body wasn't disprupted until
sometime after 3.79 Ga and you have to find some likely parent body that will
retain its nebular oxygen signature, but undergo some sort of processing - as
late as 3.79 - to result in the Sm-Nd ages and the mineral assemblage
present.
That taken together, in my mind, conclusively rules out Venus as a parent for
the ureilites. (Keep in mind there are several other lines of evidence
against
venus as well we can discuss off list if you want - unless everyone wants to
hear me keep rattling on about ureilites :) )





Steven Singletary
54-1224
Dept. Earth, Atmospheric, and Planetary Sciences
M.I.T.
Cambridge, Ma., 02139
Jumper_at_MIT.EDU

Blue Skies!!
Received on Tue 18 Sep 2001 07:30:35 AM PDT