Oxygen isotope ratios (O18 to O16) in both ice cores and cores taken from the sea bottom r

 Oxygen isotope ratios (O18 to O16) in both ice cores and
 cores taken from the sea bottom represent fluctuations
 in temperature and global ice volume (ref 1). When potassium
 argon dating (directly or indirectly) is used to give
 a timescale for these cores, and when the oxygen isotope
 ratios are spectrally analysed, they turn out to vary
 with periodicities which match (within fairly narrow
 error bars) the periodicites of certain astronomical
 parameters (such as the obliquity of the earth's orbit,
 with a periodicity of 41,000 years, and the precessional
 periods of about 19,000 and 23,000 years, as well as several
 other periods, see below for more).

 The orbital perturbations in question affect the sunlight
 reaching the earth's surface in an entirely predictable
 way, and thus affect the climate.  In other words, we
 *expect* temperature to vary at these periods, and so
 it does.  Care to explain how we can get this agreement,
 if our dating is all wrong?

 [insert july 91]

 These sea bottom cores now go back
 several million years and the astronomical periodicities
 are still there, and K-Ar dates are still in reasonable
 agreement (better than 10%) with astronomical dates.

 [original post resumed]

 The question for you, Bob, is this: Since the astronomical
 periods do *not* depend in any way on radiometric dating, and
 since these same periods show up in cores dated *by* radiometric
 dating (the dreaded K-Ar and uranium series dating) is this not
 an *independent* test of radiometric dating?  If not, why?

 The predictions as to time made by calculation of planetary
 orbits and by K-Ar dating agree very well - for a long time you've
 complained that K-Ar is not calibrated - well here it is.


 [july 91 insert]

 In recent months a 25 million year long record from the
 triassic (about 200 million years ago, for those of us
 who believe such things) has been obtained.  The rock
 is banded, and the bands form quite regular groupings.
 The smallest bands contain about 20,000 varves (annual
 layers) - and the precession cycle at that time was
 about 20,000 years long.  Coincidence?  Well, the
 precession cycle is modulated by the 100,000 year
 eccentricity cycle so the bands should occur in groups
 of five, with slightly different characteristics within
 the group.  They do.  Not enough?  There is also a
 400,000 year eccentricity cycle, so the large bands
 should be bunched in groups of four.  And they are.

 Well before this result was obtained (it hasn't even
 been published yet) a simple climate model was used
 to estimate the power spectrum of maximum annual
 temperature at a similar site [see ref 2].  The low
 frequency end of this model's output agrees
 entirely with the observations.  The cores
 have not yet been measured accurately enough to
 compare the high frequencies.

 This is quite clear evidence that these bands are
 astronomical in origin, and thus *astronomy*, not
 radiometric dating, tells us that this sample of
 rock was laid down over 25,000,000 years.
 So the earth is at least that old.  Furthermore, since
 K-Ar dating gives the same length to this record we
 have no reason for not trusting within a few percent the
 K-Ar absolute age for this stratum, which is about
 200 million years.

 Well, Bob?

 [or Allen, as the case may be]


		Bill Hyde


 References

 The geological evidence was presented by Paul Olsen of
 Lamont-Doherty at a recent workshop at Johns Hopkins.
 Preprints should exist in a few months.

 Much information on oxygen isotope measurements and
 a great deal else can be found in

 (1) "Quaternary Paleoclimatology" By R.S. Bradley
 (Unwin Hyman, 1985).



 The theoretical paper is


 (2) Short, D. A., J. G. Mengel, T. J. Crowley, W. T. Hyde
 and G. R. North 1991: Filtering of Milankovitch Cycles by Earth's
 Geography. Quaternary Research. 35, 157--173.


		Bill Hyde
Department of Oceanography
Dalhousie University,
Halifax, Nova Scotia
hyde@ac.dal.ca or hyde@dalac