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From: pamp@bcsaic.UUCP (pam pincha)
Newsgroups: net.origins
Subject: Re: Re: Orphaned Response
Message-ID: <242@bcsaic.UUCP>
Date: Tue, 27-Aug-85 16:01:54 EDT
Article-I.D.: bcsaic.242
Posted: Tue Aug 27 16:01:54 1985
Date-Received: Fri, 30-Aug-85 09:39:58 EDT
References: <14600027@hpfcrs.UUCP> <14600038@hpfcrs.UUCP>
Reply-To: pamp@bcsaic.UUCP (pam pincha)
Organization: Boeing Computer Services AI Center, Seattle
Lines: 53
Summary: 

In article <14600038@hpfcrs.UUCP> lief@hpfcla.UUCP writes:
>In article <14600030@hpfcrs.UUCP> lief@hpfcla.UUCP (lief) writes:
>>>
>>>If an organism (fossil) is found in rock strata, and one wishes to get the
>>>age of the organism, what are the steps he goes through to arrive at a figure?
>>>
>Sarima (Stanley Friesen) replied:
>>
>>	This shows little understanding of the actual conditions under
>>which fossils are found. Material incorporated into sediment while it
>>is still unconsolidated shows a quite different relationship to the
>>resulting rock stratum than would material inserted *after* the
>>sediment is consolidated. If you had ever actually watched fossils
>>extracted from sedimentary rock it would be obvious that the fossils
>>were incorporated in the sediment at the time of deposition, *not*
>>at a later time. Since the age of a sedimentary stratum is the time
>>since deposition, *not* the age of the source material, the kind of
>>error you are talking about simply can not occur.

Note:This is only one type of fossil formation! There are fossils that
can date deposition. There are several cases of fossils being IN SITU
meaning that they were buried by sediment formed at the same time they
lived (or at the momment they died - not just after. For instance
marine and deltaic storm deposites killing and burying bivalves,
echinoids and corals. That is why it is very important to determine this
(whether the fossil is in situ or transported) at time of collection.

YOU ARE RIGHT about absolute dating methods, though. Another reason
to use things like ash layers and lava flows besides that fact
that their formation is rather quick, is that they are often
rich in the material neede to perform radiometric dates. NOTE
though even the radiometric dates are teamed with more relative
dating methods to provide a more valid assesment of the age.

>     It's true that I am not familiar with dating techniques as such.  I
>had always assumed that it was the source material itself that was being
>dated rather than the time of deposition.
>Lief Sorensen
>HP Fort Collins, CO
>Uucp ...!hpfcla!lief


You are right under specific circumstances, and with certian
methods. C-14 dating requires the fossil source material to be used.
The longer half-life dating methods require generally mineral sources
that were formed under flash (geologically speaking) momments,
such as ash deposites,and lava flows.

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				P.M.Pincha-Wagener
				(bcsaic!pamp)
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