Over the weekend while doing a bit of tidying up I came across s copy I made of a scientific paper when I was arguing with a creationist about the validity of radioactive dating methods.

It is from 1988, and is relevant to the ongoing discussion we have been having recently.

One recent post mentioned just what this paper covers, so I dug out the recent post and thought I’d offer a response.

On Tue, 01 Feb 2005 one poster wrote

I find it difficult to accept that an estimation of a 50% decay rate in a million years can be made (nuclear physics, notwithstanding) and that it can be said to be uniform over subsequent millions of years of time. I’ll have to do more thinking, and where and when I can, more reading on that.

Another responded:

There are other physical processes which are cyclic or roughly linear in time which are used to calibrate (verify) each other. When several independent physical processes are consistent, that is probably the best verification that there have not been drastic changes over long periods of time.

Ken:

The paper is “A radiometric age for the Cretaceous-Tertiary boundary based upon K-Ar, Rb-Sr, and U-Pb ages of bentonites from Alberta, Saskatatchewan, and Montana”, in the Canadian Journal of Earth Science, vol. 25 (1988), pp. 1088-1097

The ages determined by the three techniques for three different locations range from 63.7 million years to 65.8 million years, with different accuracies. The accuracy for each one is quoted with the usual 95% confidence level (that is, the odds are 20 to 1 that the true result lies inside the quoted accuracy). A weighted mean gives 64.3 million years, with a 95% confidence level of plus or minus 1.2 million years. Only one of the results lies outside this, and one out of nine isn’y too surprising.

The importance of these measurements are, as Joe suggested, that here we have three independent measurements agreeing with each other, withing the limits of accuracy of measurement, so we can say with a great degree of confidence that the boundary is very close to 64 milliuon years ago.

The greatest significance, however, lies in the fact that three different modes of radioactive decay are involved. Now this is where I am going to get a bit technical, so people might like to skip the next paragraph and go to the following one – but as a common saying goes, the devil is in the details, and if creationists want to disagree they will have to come up with a detaioled analysis of how they thing radioactive decay happens, and their views of the fundamental physical forced.

There are four fundamental physical forces at work in the universe: gravity, the electromagnetic force, the weak nuclear force and the stroing nuclear force. Gravity can be neglected, since it is extremely weak compared with the other forces (the electromagnetic forces exerted by your muscles are easily able to overcome the gravitational force due to the whole mass of the Earth). Initially people discovered three types of radiation from radioactive materials, labelled alpha, beta and gamma. Gamma radiation is simply very short wave electromagnetic radiation. Alpha radiation consists of helium nuclei, and beta radiation consists of electrons. In alpha decay a helium nucleus is ejected from the nucleus, and the rate at which this occurs is determined by the relative strengths of the electromagnetic force and the strong nuclear force (I am simplifying things somewhat here to avoid unnecessary verbiage). In beta decay an electron is ejected from the nucleus, and the rate at which this occurs is determined by the electromagnetic and weak nuclear forces.

Later it was discovered that in some cases an electron from the inner shell of electrons in an atom can be absorbed by the nucleus, and this is known as K-capture. The rate at which this occurs is also determined by the electromagnetic and weak nuclear forces.

Now of the three dating methods used, K-Ar (potassium-argon) decay involves K-capture, while Rb-Sr (rubidium-strontium) decay is beta-decay. If you look back to the previous paragraph you will realise that these two are, essentially, the same process, but going in opposite directions. Now if the relative strengths of the electromagnetic and weak nuclear forces changed, the decay rates for these would change in opposite directions. But since the dates obrtained agree, we can assert, with confidence, that there has not been any significant change in these two forces.

U-Pb (uranuim-lead) decay is more complicated, since it involves a chain of decays involving both alpha and beta decay. All three forces are involved here, but since the strengths of the electromagnetic and weak nuclear forces haven’t changed, and the dates of U-Pb agree with the other two, we deduce that the strong nuclear force hasn’t changed, either.

Thus all three forces have remained unchanged, at least for more than 60 million years.

This is just one example backing up Joe’s statement “When several independent physical processes are consistent, that is probably the best verification that there have not been drastic changes over long periods of time.”

I don’t think we can do much better than this sort of evidence. There are other lines of evidence, but they tend to be even more technical than this one.

Salaam Ken Smith

— Dr Ken Smith – Christian, husband, unpaid mathematician, skeptic, … `No non-Christian geologist is ever going to accept Flood geology or the young-Earth theory these days; the flaws and weaknesses are obvious to any practicing geologist.’ Davis A. Young