Radioactive Dating and Helium Diffusion - Confirmation of the Biblical Time Scale
From the March 2005 Creation Answers Newsletter
by Wayne Spencer
In the past two newsletters we have looked at radioactive dating techniques and at reasons their results are not reliable. In this issue we will look at the isochron technique and at new research on Helium diffusion that gives an exciting confirmation of the Biblical age of the Earth.
There are three key assumptions of radioactive dating techniques that have been called into question by young earth creationists. See the Sept. 2004 issue of this newsletter for more details on this. The First of these is that there is a constant decay rate of the radioactive elements. Creationists now have done their own experimental research that calls this assumption into question. The research on Helium diffusion in zircon crystals that follows is one line of evidence to that effect.
Other major assumptions of radiometric dating are that the sample has been a closed system while the decay occurred and that the initial concentrations of the radioisotopes is known. In real rocks and minerals, the closed system assumption would mean that there was no non-radioactive process that changed the amounts of the radioactive elements while the radioactive decay was taking place. This assumption is seldom completely valid. There are always other processes that “interfere” with the age calculation. Scientists try to account for these other processes. There is a tenancy for there to be unaccounted for processes that either take away the parent isotopes or add to the daughter isotopes, making the radiometric age figure turn out too large. The initial concentration assumption has to do with knowing the starting conditions of the mineral that the decay took place in. If the age calculation incorrectly assumes there was none of the radioactive daughter element present when the rock formed, this will throw off the age result. Daughter elements present when the mineral formed can make the sample seem older than it really is, if it is not accounted for properly in the calculation.
The Isochron Technique
The isochron dating technique was devised as a way to avoid errors caused by the assumptions above not being true. The technique provides what’s believed to be a self check of the second and third assumptions above.
In the isochron technique, the concentrations of the radioisotopes are used to calculate certain ratios and these are plotted on a special graph such as the graph below. For this graph, Rubidium-87 (Rb-87) decays into Strontium-87 (Sr-87). Strontium-86 is not radioactive and thus it is used as a reference. If there was no radioactive decay, the line connecting the three samples would be perfectly horizontal. But as Rb-87 decays into Sr-87, this makes the slope of the line move up as more and more Sr-87 accumulates in the rock. The point where the line through the samples intercepts the vertical axis (0.70) is believed to give the initial concentration of the daughter element, Sr-87. If the points plotted for the samples do not line up on a straight line, this is taken to mean that the samples were not a closed system.
Radiometric dating techniques, other than the Carbon-14 method, can only be used on igneous and metamorphic rocks. They cannot be used in sedimentary rocks. This means radiometric dating methods (other than C-14) are not used to date fossils directly. Sometimes there are contradictory results such as when a piece of wood is buried by a lava flow from a volcanic eruption. The wood is known to be older than the lava flow but the lava flow will date to be millions of years in age but the wood may only date to be thousands of years.
There are also cases where multiple radioactive dating methods are used on similar samples so that their results can be checked against each other. There are also studies in which the individual mineral grains in a rock are dated as well as other minerals from the same rock, so that the two results may be compared. There are sometimes significant disagreements between these different radiometric methods. Creationist geologist Steve Austin has documented examples of such “discordant” results in the Grand Canyon. Samples from the top of the Canyon, from the Uinkaret Plateau dated older by hundreds of millions of years than rock taken from some of the deepest and oldest layers in the Canyon (the Cardenas Basalts and the Diabase Sills). There are also various processes that can cause radiometric dates to plot in a straight line on an isochron graph, though the age figure is known to be impossible because of other evidence. Much has been published by the Institute for Creation Research on this research. The proceedings of the International Conferences on Creationism also include important papers on these topics by Dr. Andrew Snelling or by Doctors Austin and Snelling.
Thus, isochrons may look valid from being beautiful straight lines and the evidence from radiometric dates may sometimes appear to fit evolutionary ages. But creationists are beginning to be able to explain why the various methods appear to work sometimes and why they do not work in other cases. This involves lot of technical details I will not go into in this newsletter. The bottom line is that no radiometric methods work reliably, with some possible exceptions for Carbon-14 for ages less than about 4,000 years (since Noah’s Flood). However, in the light of recent creationist research, it may be possible some day to correct at least some radiometric age calculations. There is evidence of trends in the ages given by the various radioisotopes that are not yet understood. For example alpha decay isotopes give older ages than beta decay isotopes.
Helium Diffusion in Zircons
Creationists from the R.A.T.E. research project have completed some interesting studies that challenge conventional thinking regarding the radioactive decay of Uranium. In 1974, Los Alamos National Laboratory commissioned drill cores to be dug at a site in the Jemez Mountains in New Mexico in an effort to look for geothermal energy sources. In 1982 creationist scientist Robert Gentry published a controversial result in which he measured the amount of Helium retained inside certain crystals from some of these drill cores. The mineral biotite from these samples contains crystals known as zircons. “Zircon” is a shortened name for zirconium silicate. These crystals were radioactive. They contained products from the radioactive decay of Uranium-238. Uranium-Lead dating results done by evolutionist scientists gave values of about 1.5 billion years for the age of the biotite rock from the drill cores. This was consistent with what geologists accept for the age of that rock unit. For every Uranium-238 atom that decays inside one of these zircon crystals, eight Helium atoms are produced (from the alpha particles given off). Now Helium is a pretty small atom and it does not react chemically with other substances, and so it has a tendency to find its way out. It will escape the crystal and Robert Gentry was the first to notice that the amount of Helium present in the zircons did not agree at all with the very old age that geologists accepted for the crystals. Gentry’s measurements were not taken very seriously apparently by the scientific community. But in the past few years, creationists from the R.A.T.E. research project have done further experimental studies that validates Gentry’s measurements and the results are an exciting confirmation of Biblical chronology.
The R.A.T.E. team obtained samples from the same drill cores and contracted with a high precision laboratory to measure the Helium diffusion rate from the zircons in the biotite samples. Prior to the R.A.T.E. project, there had been very little interest in measuring Helium diffusion in zircons by the scientific community. In fact, apparently no one had measured it in biotite minerals. Laboratory work was done at two different times for the R.A.T.E. project, with the final results published in the June 2004 issue of the Creation Research Society Quarterly. Following is an excerpt from the Abstract of that paper:
'The measured rates resoundingly confirm a numerical prediction we made based on the reported retentions and a young age. Combining rates and retentions gives a helium diffusion age of 6,000 ± 2,000 years. This contradicts the uniformitarian age of 1.5 billion years based on nuclear decay products in the same zircons. These data strongly support our hypothesis of episodes of highly accelerated nuclear decay occurring within thousands of years ago. Such accelerations shrink the radioisotopic “billions of years” down to the 6,000-year timescale of the Bible.'
These results are very significant. In the uniformitarian or old age view, the diffusion rate of Helium would need to be about 100,000 times slower than the measured values in order to explain how the Helium could still be there after over a billion years. But the young age view predicted diffusion rates that agreed very well with the quantities of Helium. Some scientists from the old age point of view might suggest that there was slower Helium diffusion over billions of years of Earth history until something caused a rapid diffusion several thousand years ago. But, this does not work because in the uniformitarian view of Earth history, the temperature of the minerals would be higher in the past, which would make diffusion even more rapid. In order to slow the diffusion down so the Helium would be retained for 1.5 billion years, the crystals would have to be somehow refrigerated to about -100 degrees Celcius!
The R.A.T.E. results are confirmed by another product of the Uranium decay, which is Lead. Lead is produced by this decay and it also diffuses out of zircon crystals. The diffusion rate of Lead in zircons was measured by Robert Gentry as well. When this is applied to the R.A.T.E. measurements it agrees very nicely with the new data and a 6,000 year age.
Conclusions of the Helium diffusion studies are 1) Gentry’s Helium retention result is confirmed and 2) the uniformitarian view of the Helium in these crystals seems to be falsified. In addition, the concept of an accelerated radioactive decay rate in the past seems reasonable for these reasons. First, the radioactive Uranium decay products present in the zircons shows there was definitely a great deal of decay that occurred. Second, the Helium produced by this decay, considering the temperature and conditions in the rock, would diffuse out relatively rapidly. This means a young age of roughly 6,000 years agrees with known straightforward physics about the diffusion of Helium through zircon crystals. The diffusion process has to do with what happens to the products of the radioactive decay, not with the decay process itself. The 6,000 year figure determined by the R.A.T.E. team does not depend on assumptions about nuclear decay.
I would say this evidence from Helium diffusion is probably one of the best arguments for a young Earth that creationists have. It agrees beautifully with the Bible and it has some very careful research behind it. Thus there are ways of answering challenges from evolutionary science, though we always have more to learn.
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