Re: [pinhole age of rocks]

Date view Thread view Subject view Author view

From: Geoff Ruth (geoffreyruth@usa.net)
Date: Wed Dec 08 1999 - 20:20:02 PST 

Message-ID: <19991209042003.18904.qmail@nw176.netaddress.usa.net>
Date:  8 Dec 99 20:20:02 PST
From: Geoff Ruth <geoffreyruth@usa.net>
Subject: Re: [pinhole age of rocks]

Sally Seebode <sseebode@earthlink.net> wrote:
> Hi all;
> Last night I was attending my regular Tuesday Ed class accumulating
> credits and listening to the fabulous Paul Doherty. He was talking about
> magnetism, and I forgot to ask how we know the age of rocks? It's
> obviously not carbon dating, but is there another radioactive substance
> that all rocks contain? or is there a totally different method?
>
> So, I'm asking all of you: How do scientists determine the age of rocks?

Geologists use other radioactive isotopes besides C14 for dating longer
periods of time. Some other decay sequences used to date rocks include:

U-238 decays to Pb-206 with a half-life of 4.5 billion years
U-235 decays to Pb-207 with a half-life of 713 my
Tl-232 decays to Pb-208 with a half-life of 14.1 by
Rb-87 decays to Sr-87 with a half-life of 47 by
K-40 decays to Ar-40 with a half-life of 1.3 by

In dating a rock of a certain age, you'd look for isotopes with a half-life
closest to how old you hypothesize the rocks are.

____________________________________________________________________
Get free email and a permanent address at http://www.netaddress.com/?N=1

Date view Thread view Subject view Author view

This archive was generated by hypermail 2b29 : Thu Oct 19 2000 - 11:10:03 PDT