R.A.T.E. and Helium Diffusion

Okay, as I am currently engaged in a course in Geochronology, and my final paper covers the ridiculous claims of R.A.T.E., the ICR/CRS joint effort to assault the iron gates of radiometric dating, I thought I would post what I am researching as a means of helping others understand the craziness of this particular "research team." My contribution for the benefit of all.

This will be in several installments, as I complete my own research on each.

Helium Diffusion:
The experiment into rates of helium diffusion was conducted primarily by Dr. Russell Humphreys. He worked closely on the project with another man who is a bit of an icon among creationist circles, none other than Dr. Robert Gentry. It was Gentry who first proposed the idea that radiohalos found in mica might indicate a creation in situ of a parentless daughter radioisotope, polonium, thus showing the rocks were created, not metamorphosed. His ideas were not taken seriously, even after he published a book detailing his ideas, and a promised second volume which would go into greater detail never surfaced. His second volume, it seems, found itself via collaboration with the RATE team.
Although Humphreys’ initial proposal dealt with He diffusion in biotite, the focus was later shifted to zircons, where alpha decay could be more accurately determined in order to quantify exactly how much helium had been produced. The zircon samples he used came from core samples, taken from varying depths of a drilling site at Fenton Hill, just west of the volcanic Valles Caldera in the Jemez Mountains near Los Alamos, New Mexico.[1] Temperature readings were taken at each core sample at varying depths, so that a correlation could be drawn between how much helium had been retained at each temperature. Some of the samples were provided by the Los Alamos National Laboratory to the Zodiac Minerals and Manufacturing Co. – a small mining company which acted as a liaison between for the more secular labs and the RATE team.[2] Other samples were from Robert Gentry’s own sample collection, as he had previously used samples from that site in his earlier work on polonium halos.[3]
The amount of lead daughter product in the zircons was measured, and because the paths of decay from uranium and thorium to lead generate an average of 7.7 helium atoms per each lead atom produced, he used this to estimate the amount of helium generated, which he called Q0. He then determined the amount of helium which had been retained in the sample zircons, sending them to the Activation Laboratories in Ontario, Canada. The rates of He diffusion at various increasing temperatures, D, was measured, and the total amount of He retained, Q, was determined.
When this was plotted out, it was found that the amount of He retained was significantly higher than what might be expected, given the rates of diffusion. There was about 1.5 billion years worth of accumulated lead daughter product in the zircon, but over that span of time, according to what Humphreys calls the Uniformitarian model,[4] the amount of helium left inside the zircon should now be much lower – on the order of 100,000 times less! What could the explanation be?
According to Humphreys, there can be only one explanation. Clearly, at some point in the past, the rate of radiogenic decay was much faster, or accelerated. This rapid rate of decay caused a large amount of He to be trapped within the zircon within a relatively short amount of time. Since then, the rate has slowed and He has been diffusing, but it has only had roughly 4,000 – 6,000 years in which to do so. This is why so much He yet remains inside the crystal.
So what’s wrong with this picture? Dr. Kevin Henke, a geologist at the University of Kentucky, points out three obvious problems.[5] First off is the measured rates of diffusion. Humphreys had the zircons’ diffusion rate measured in a vacuum with increasing temperatures. But this would not mirror the conditions of heat and pressure found at Fenton Hill, where the rocks were beneath tons of rock, surrounded by the pressure of other minerals. Second, the samples came from a region near the Valles Caldera, a volcanic region known to harbor amounts of extraneous helium. In particular, Humphreys should have tested for contaminants of 3He and 4He. Thirdly, his estimates of the amount of initial uranium may have been wrong, based in part on the observations and notations made in Robert Gentry’s earlier work. This means that his estimates of his “creation timescale” may be too small by as much as one complete order of magnitude.
The fact that helium diffusion rates are much faster in a vacuum are enough to categorize Humphrey’s results as inaccurate. Scientists such as MacDougal and Harrison[6], as well as Dalrymple and Lanphere[7] have long since shown that diffusion of noble gases in silicate minerals may decrease by as much as 3-6 orders of magnitude at a given temperature if the studies are done under pressure as opposed to in a vacuum. And while Robert Gentry’s earlier work gave Humphreys access to a number of readily available samples to work with, he might have been better off choosing a fresh site – one which critics would not be able to point out such an obvious source of contaminating helium as a nearby volcano. All in all, some rather sloppy work.

[1] The site had been drilled in the 1970’s as a potential source of geothermal energy.
[2] A go-between was clearly needed since some scientists might rightly have grave concerns over giving samples to a known creationist group with a declared agenda.
[3] That meant the samples were collected in 1982. The zircons in the biotites he’d collected were relatively untouched.
[4] Even though the term, Uniformitarian, is almost never used anymore.
[5] http://www.talkorigins.org/faqs/helium/zircons.html
[6] McDougall, I. and T. M. Harrison, 1999, Geochronology and Thermochronology by the 40Ar/39Ar Method, Oxford University Press, New York.
[7] Dalrymple, G.B. and M.A. Lanphere, 1969, Potassium-argon Dating: Principles, Techniques and Applications to Geochronology, W.H. Freeman and Co., San Francisco.