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

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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


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