Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.2 9/18/84; site 3comvax.UUCP
Path: utzoo!watmath!clyde!burl!ulysses!allegra!oliveb!3comvax!michaelm
From: michaelm@3comvax.UUCP (Michael McNeil)
Newsgroups: net.origins
Subject: Re: Radiocarbon errors
Message-ID: <236@3comvax.UUCP>
Date: Thu, 26-Sep-85 21:50:17 EDT
Article-I.D.: 3comvax.236
Posted: Thu Sep 26 21:50:17 1985
Date-Received: Sun, 29-Sep-85 06:49:27 EDT
Distribution: net
Organization: 3Com Corp; Mountain View, CA
Lines: 105

[Oh, *please* don't eat me, Brer Line Eater Monster, Sir!]

Reference: article <180@3comvax.UUCP>

> Pray tell, then, how we can trust things like U-235 or U-238 since we
> don't have any supporting evidence to test it against?
> 
> If C-14 can be off by so much, so can methods that supposedly date
> things much older. One should note well the studies (Michigan State, I
> believe) which found major differences in dates provided by different
> long-term (e.g., K-Ar, Rb-Sr, U-Pb, Th-Pb) methods.
> 
> Larry Bickford, {amd,sun,decwrl,idi,ittvax,cbosgd}!qubix!lab

Thanks for writing, Larry.  Sorry to be long in answering, but I had
intended to take more time researching my reply, with the thought of
posting it for others who might also be interested.  Unfortunately,
I don't have time to do it well right now, so I'll reply briefly.  

The original article discussed carbon-14 dating rather than other,
longer-term radioactive dating methods, but I grant you that the
question of the one method leads quite naturally to the others.  

There is an important qualification which it's necessary to keep in
mind when discussing variances in C-14 deposition over time.  The
rate of *decay* of carbon-14 does not vary, rather the rate of the
*creation* of C-14 changes as the flux of cosmic rays changes.  Once
created, carbon-14 -- and all other radioactive isotopes -- decay at
a constant rate.  (Radioactive decay stems from the "weak" nuclear
force, which so far as is known, is affected by practically nothing.)  

Unlike carbon-14, the other radioactive isotopes such as uranium
and radium all derive, with the exception of a trifling amount of
matter which arrived on meteorites, from the origin of the Earth.  
Either elements are left over from the beginning, such as uranium
and thorium are, or the element is derived from the decay of other
radioactive elements, such as is the case for radium, tritium, etc.  

Uranium is a particularly good candidate for dating with, since
due to its long half-life, much uranium still exists on the Earth.  
Also, uranium-235 and uranium-238 are naturally mixed in constant
proportions on Earth, so they provide a check against each other.  
When this is done, the results generally check out consistently.  
Comparing uranium-derived dates with dates found using other
radioactive elements also generally cross-checks consistently.  

In addition, radioactive dating is continually checked against
other, non-radioactive dating methods, such as the fossil and
geologic record.  These records in a way are quite similar to
tree-ring dating.  Like the tree rings, sequences of datable
events are interspersed with the events of interest.  The
"tree rings" in this case are the alternating sequences of
lava flows and sediment layers found all over the world.  

The lava flows contain the radioactive materials, trapped in
their exact proportions as of the time the lava cooled.  The
sediments contain fossils, which identify the epoch when the
sediments were deposited.  When it is the radioactive clock
that is being calibrated, known fossils provide dating which
calibrates the degree of radioactive decay which has occurred.  
Then, when the radioactive-decay clock is properly calibrated,
unknown fossils located in other sediments can be dated using it.  

Finally, to show that rates of radioactive decay *have*
remained constant over time, several years ago a *natural
reactor* was discovered in Africa.  Geologically dated to a
period several billions of years ago, the reactor -- a bed of
uranium ore -- went critical, heated up, and quietly melted
down a number of times over a long interval.  Now, no uranium
ore *can* approach critical nowadays, since uranium-238 can't
fission normally, and the proportion of fissionable uranium-235
is too low in uranium today.  No, the reason that the ore could
go critical back then is simply due to the relative decay rates
of U-235 and U-238 -- the shorter half-life of U-235 resulted
in a higher proportion of U-235 to U-238 in that epoch.  

As for the Michigan State study you mentioned, I'm not familiar
with it.  It's a frequent occurrence on the frontiers of science,
however, for preliminary results to be ambiguous or at variance
with other researchers' results, only for the problem to be
resolved later with better equipment and experiments.  I suspect
that's what has happened here.  I assure you that scientists
cannot forever ignore *genuinely* contradictory evidence --
too many of their colleagues would *love* to catch them at it!  

However, if you would like to forward me more information about
the Michigan study you mentioned, I'll attempt to evaluate it.  

-- 

Michael McNeil
3Com Corporation     "All disclaimers including this one apply"
(415) 960-9367
..!ucbvax!hplabs!oliveb!3comvax!michaelm

	Who knows for certain?  Who shall here declare it?  
	Whence was it born, whence came creation?  
	The gods are later than this world's formation;
	Who then can know the origins of the world?  

	None knows whence creation arose;
	And whether he has or has not made it;
	He who surveys it from the lofty skies,
	Only he knows -- or perhaps he knows not.  
		*The Rig Veda*, X. 129


Brought to you by Super Global Mega Corp .com