Re: pinhole Rock Dating

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From: Paul Doherty (pauld@exploratorium.edu)
Date: Fri May 06 2005 - 09:40:17 PDT 

Message-Id: <86FDB829-BE4D-11D9-BDED-000A95B38012@exploratorium.edu>
From: Paul Doherty <pauld@exploratorium.edu>
Subject: Re: pinhole Rock Dating
Date: Fri, 6 May 2005 09:40:17 -0700

Hi Joe

The key to rock dating is chemistry.
When a mineral such as uranite, UO2 crystalizes it is composed almost
entirely of uranium and oxygen. It forms in the shape of a fluorite
crystal an octahedron.
There is no lead in the initial crystal at all.
Then over time the uranium decays to lead, one isotope U238 decays with
a halflife of 4.5 x 10^9 years
that means if a crystal of uranite formed at the birth of the solar
system, 4.5 billion years ago, then now half of the uranium's in the
crystal would be lead atoms.
In fact this is exactly what we find in meteorites and is one of the
strong pieces of evidence that the meteorite crystalized 4.5 billion
years ago and so the solar system must be this old (or older. )

Paul D

On May 5, 2005, at 8:39 PM, jleet1972@netzero.com wrote:

>
> If someone could help me with this. I am a little confused about the
> dating of rocks. Is it primarily based upon Uranium decay, and is it
> compared to some standard?
>
> Thanks
>
> Joe
>
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