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.
[or Allen, as the case may be]
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.
Department of Oceanography
Halifax, Nova Scotia
email@example.com or hyde@dalac