[meteorite-list] what is the most primitve meteorite? or do we even know?

From: star-bits at tx.rr.com <star-bits_at_meteoritecentral.com>
Date: Wed, 16 Apr 2008 0:52:14 -0400
Message-ID: <18059983.984881208321534674.JavaMail.root_at_cdptpa-web26-z02>

---- Dark Matter <freequarks at gmail.com> wrote:

<Here's a link to Eric's site stating Vigarano as the (consistently)
 oldest meteorite. Maybe Eric can shed more light on his statement.>

Here is what I wrote on my web page.

<A case can be made for Vigarano being the oldest meteorite. Although older ages have been recorded for other meteorites they are isolated measurements and do not give as consistently an old age as does Vigarano. >

    First let me say that my comments were about relative age and not how primitive vigarano is. As Jeff mentioned that is another matter entirely.

    Second there are different methods for determining age. Absolute age is how long ago something happened and is given by isotopes with long decay ages like Uranium-Lead. Relative ages at the beginning of the solar system are determined by extinct isotopes with short decay ages. The basic premise is that the solar system was salted with a dose of these isotopes and as time passes there is less and less of the isotope that is decaying. So the earlier a solid forms the more of this isotope it has and as a result there is more of the decay product locked into the structure of the solid.

     So for relative ages one meteorite was picked as the zero point and the rest are either younger or older in relation to it. For the life of me I can't remember what was used as the zero point

     The third point is that there are different sampling methods. A sample can be either "whole rock" ie representative of the meteorite as a whole or samples of specific parts, clasts, CAIs etc. So if you are aging samples taken from different points on a meteorite they can give different ages if you are sampling a CAI or a part that accreated slightly earlier or later than the rest of the meteorite. At the time my statement was written (6 or 7 years ago) I was told that there were samples that were older than vigarano however those early dates were not representative or consistent for those meteorites as a whole. Vigarano however gave consistently old relative dates even if they were not the the oldest ever recorded. That is the basis of my statement. However 6 or 7 years is a long time in the science of meteorites, does anybody know of any research that makes my statement invalid today?

--
Eric Olson
7682 Firethorn Dr
Fayetteville, NC 28311
http://www.star-bits.com

Received on Wed 16 Apr 2008 12:52:14 AM PDT