From: hyde@cs.dal.ca (Bill Hyde)
Subject: Re: Help needed to debunk creationism
Organization: Math, Stats & CS, Dalhousie University, Halifax, NS, Canada
Date: Tue, 25 Aug 1992 16:01:14 GMT

In article <930@tdat.teradata.COM>, swf@teradata.com (Stanley Friesen) writes:
|> In article <25147@castle.ed.ac.uk> eftv03@castle.ed.ac.uk (L R Watt) writes:
|> |
|> |1. Does someone have information on the dating of coral,
|> |   lake-bed sediment, ice cores, tree rings etc?  My
|> |   colleague thinks these methods are extremely unreliable,
|> |   or even completely at odds with other dating techniques,
|> |   and insists that climatic change in the past would 
|> |   give spurious indications of an old Earth.  
|> 
|> All creationists think all dating techniques are unreliable - they have to
|> in order to make their position even remotely plausible.
|> 
|> As for the dating methods mentioned, they are generally held to be the
|> *most* accurate of all of them (they are the only ones that come even
|> close to one year resolution).  They are not at odds with any other dating
|> method, they complement them rather nicely.  In fact tree ring dating has
|> been used to calibrate the carbon-14 time scale.  The result is that now
|> the C-14 time scale is extremely accurate back to about 50,000 years.


	Actually, tree ring calibration is only good for about the
	past 10,000 years, for the simple reason that that is the
	length of the longest dendrochronological record.  Research
	continues, however, and longer records are likely to be
	available soon.  For times prior to 10,000 years, C-14
	dates are calibrated by uranium/thorium dating.  I would
	not believe any 50,000 year old C-14 date without substantial
	error bars, unless the size of the sample were huge.



|> 
|> Beyond that none of the detail methods are much good for *dating* anyway,
|> though some may still be used for establishing *local*, *relative*
|> chronologies.  (Actually, ice-cores are almost as good as C-14, and
|> can be used further back than any of the others you mentioned)
|> 
|> The whole *point* of methods like ice-core and tree ring dating is to
|> adjust for climatic changes!  That is why tree ring dating was used to
|> calibrate the C-14 scale (the C-14 scale *is* climatically sensitive,
|> but only at about the 5% level).

	It is more sensitive to changes in the earth's magnetic
	field, which affects the number and intensity of cosmic
	rays hitting the upper atmosphere, which are the indirect
	source of C-14 generation.  Since C-14 dating assumes that
	the amount of C-14 in the atmosphere is constant this can
	affect dates by as much as 20%.  Thanks to calibration, this
	is not a fundamental problem.


|> 
|> For times more than about 100,000 years ago only long-term radio-isotope
|> dating, or its derivative forms, is much good (for example Rubidium-Strontium
|> dating, or the less accurate Uranium dating).

	Uranium/Thorium dating is no longer less accurate.  It is now
	quite remarkably good. Uranium series dating has always
	held considerable promise, but the technical problems
	were considerable.  For certain types of sample these
	problems have now been solved. Progress is being made
	in Amino-acid dating, which for tropical sites (where temperature
	changes have been limited) may be accurate out to about 200,000
	years before present.  At the momemt most amino-acid dates have
	*large* error bars.

	Rubidium-strontium dating cannot be used for times as short
	as 100,000 years  as the amount of decay product is quite
	small (half life 47 billion years) - even potassium/argon  dates
	are not usually cited under a few hundred thousand years.
	Between the end of C-14 reliability and the onset of K/Ar there
	are the various uranium series and thorium series techniques,
	Thermoluminescece, fission track, amino acid, and (for ice and
	sea cores) astronomical dating.  The latter is not much used,
	but provides a good check on the others, for example it was
	astronomical dating which provoked a reexamination of the
	Brunhes-Matuyama K/Ar date, which has recently been reassigned
	to about 780,000 years ago from 730,000 years ago.



|> |2. What is the evidence that radioactive isotopes have
|> |   constant decay rates over geological time?


	Decay rates cannot change in isolation.  All of nuclear
	physics (perhaps all of physics, period) would have to
	change for these rates to change.  In this case our
	stellar models would not work nearly as well as they
	do.  When an astronomer looks at a star 200,000 light years
	away he is actually looking 200,000 years into the past.  If
	decay rates were different then, the star should be behaving
	very strangely.

	Also, astronomical dating (based on the, in principle, simple
	task of calculating changes in the earth's orbit and therefore
	independent of decay rates) agrees well with radioisotope
	dating.

	[concerning hydrodynamic sorting and the flood]


	Fossilized lakebeds.  In some formations we see a column consisting
	of lakebed rock, formed from silt and with typical freshwater
	fauna, then typical marsh flora and fauna, then a layer formed
	from dry, dessicated soil in which the fossils are land animals,
	followed by lakebed rock.... and the cycle repeates several times.

	Now climatologists have an explanation for this, since these
	fluctuations follow perturbations in the earth's orbit which
	are calculable.  These perturbations seem to have a strong
	effect on the level of tropical lakes, in fact recent studies
	of the history of african rift lakes show that they were
	much smaller some tens of thousands of years ago, when the
	orbital configuration was different from today's.

	Now, how do you get the structure, lake - marsh - dry plain,
	repeated many times, in a 40 day flood?  Or even in a 40 year
	flood?  How can a flood produce layers of dry sand, anyway?





						Bill Hyde
Department of Oceanography
Dalhousie University,
Halifax, Nova Scotia
hyde@Ice.ATM.Dal.Ca or hyde@dalac
Newsgroups: talk.origins