Helium Diffusion as a Creationist Clock

By Michael Ward

Scientists use certain elements present in a certain abundance to calculate an approximate age for rocks. One of the decay ratios used is 238Uranium decaying through a series of alpha and beta decays to 206Lead. (The number in superscript preceding the element name indicates the atomic mass, the sum of its protons and neutrons.) Alpha decay releases a Helium nucleus (two protons and two neutrons) from the parent atom to create two atoms: the released Helium and a daughter product that has an atomic number two less than the original and an atomic mass four less than the original. Using the amount of the remaining 238Uranium, the amount of 206Lead that has built up, and the original amount of 204Lead which is not created by any known decay process, scientists can calculate an approximate age based on the decay rate of 238Uranium and the ratios of 238Uranium to 204Lead and 206Lead to 204Lead.

Some creationists claim that there is too much helium in Earth's crust for the earth to be any more than two million years old (Sarfati, 2005). If Earth has existed for billions of years, there should be little helium left in deeper rocks as a result of radioactive alpha decay. They claim that if God had created the Earth with initial Helium in the atmosphere, the maximum age would be even lower than two million-perhaps even as little as 6,000 years (Humphreys et. al., 2005). The RATE (Radioisotopes and the Age of The Earth) project, cosponsored by the Institute for Creation Research, the Creation Research Society, and Answers in Genesis, claims that the amount of helium present in minerals at different depths of the earth's crust is too high to support day-age or evolutionist theories about an old Earth. They sent rock samples to a lab for helium diffusion tests, and their results were that the rock samples have too little resistance to the diffusion of Helium through the rock for the age to be greater than at most two million years.

The conclusion reached by the RATE project as to the reason for the increased amount of Helium is that sometime in the past few thousand years there was a period of increased radioactivity (DeYoung, 2005, 78). A fundamental problem with this hypothesis, however, is that the amount of energy released during the accelerated decay proposed by RATE would potentially be enough to evaporate the oceans and melt the Earth's crust (Ross, 2004, 179).

The samples RATE tested were from a borehole sample retrieved in 1974 with no statement made as to the storage or collection conditions of the samples. In a statement on page 72, the report states that "[t]hey were taken from a depth of 750 meters, where the temperature was measured at a constant 96°C" (DeYoung, 2005). Was the rock sample kept at the same temperature and pressure during storage as that it would have experienced had it remained in the ground? Was there any chance of helium from any other sources contaminating the sample? In order to fully quantify the rock samples they obtained, the above two questions need to be thoroughly answered to secure the quality of the rock being sampled. However, neither of these questions were answered, and the wording of the paragraph indicates that the samples that were sent to the laboratory were excavated thirty years previous and not fresh.

Even with an obvious lack of sample documentation there is other substantial criticism of the accuracy of the findings of the RATE project. One major critique was written by Kevin Henke, Ph.D (Henke, 2005). His criticisms range from using faulty standard deviation for error factors to incorrectly identifying rock samples that could lead to very serious errors in measurements to using equations that yield inconsistent dates as examples of how traditional radioisotope dating is flawed. For example, the project's final results were an age of 6,000 ± 2,000 years; the standard deviation should have been 6,000 ± 4,600 years (Henke, 2005). There are also questions about the purity of some of the rock samples that were claimed to be of high purity: in an appendix to the final report, the lead scientist expressed some confusion as to the behavior of a rock sample which can only be explained as impurities in the sample (Henke, 2005).

Another major problem is that the the diffusion measurements were taken while the samples were in a vacuum. Gases readily try to expand and fill all available space, and a vacuum acts just as one imagines: it "pulls" the gas out of the rock much faster than it would ordinarily move when confined in cubic miles of rock. The diffusion values that were measured (the amount of gas that came out of the rock in a certain period of time at certain temperatures) were used as equivalent values to the natural environment (Henke, 2005).

Another serious procedural error is that there is no distinction in the amount of Helium diffused that separates 3Helium from 4Helium. One may wonder why such a detail would matter; after all, Helium is Helium, right? Most of the 3Helium would not have been caused by decay while most-if not all-of the 4Helium would be the result of decay, so to simply state that a certain amount of Helium diffused from the rock would be inaccurately representing the facts.

Scientists usually look at the daughter product of the decay in order to determine the approximate age of a rock or mineral. The reasoning for this is that the helium release by alpha decay can too easily escape the surrounding rock. In the case of 238Uranium, the daughter product is 234Thorium. Through many decay sequences, it eventually decays to become 206Lead. Using the slope of an isochron graph, an approximate age can be calculated for the sample.


Figure 1: An example isocron. The x-axis represents the increasing amount of parent element; the y-axis represents the increasing amount of daughter product. (Stassen, 2005)

An isochron graph uses the present ratio of, in this case, 206Lead to naturally-occurring 204Lead graphically plotted against the present ratio of 238Uranium to 204Lead to determine the age. In this example, the mineral started out with a certain ratio of 206Lead to 204Lead and a certain ratio of 238Uranium to 206Lead. Over a long period of time, the parent element will decay at a calculable rate into the daughter product. With more of the parent product existing in the rock sample, more of the daughter product will have been created; with less of the parent product existing in the rock sample, less of the daughter product will have developed. The resulting plotted points should line up near a single sloping line which is then used to calculate the age.

If there are any impurities in the dated samples, the final result will not have points on a line; the points will be scattered about with very little correlation to each other. In Figure 2, one sample has been contaminated by gaining some of the parent product, and another sample has been contaminated by losing some of the parent product. These two contamination events alter the isochron line so that no accurate conclusion can be drawn.

impact of contamination on an isochron

Figure 2: The result of an isochron from contaminated samples (Stassen, 2005)

In alpha decay, two protons and two neutrons are released: a 4Helium atom. This atom is much smaller than Oxygen, Silicon, and other elements that form the earth's minerals, so it is easily able to slip between the mineral molecules to escape through rock. An element such as 206Lead cannot migrate very far through a mineral because it cannot fit between the bonds of other, smaller atoms. At higher temperatures, Helium will have an easier time escaping from rock, though higher pressures found deeper within the crust will slow the Helium down. The ability of Helium to migrate through rock makes it very hard to consider it a reliable dating source. It is much easier to use an element that has very little ability to migrate than one that has a great ability to move in and out of rock.

The major problem with using Helium as a measure of age is that alpha decay always releases a 4Helium nucleus. Uranium is only one of many radioactive elements that decay to a stable element through alpha decay. In the process of decaying to 206Lead, 238Uranium releases 8 4Helium nuclei (Lupton, 2005). 222Radon also decays through alpha decay to 206Lead. While 222Radon is a daughter product in the decay chain from 238Uranium to 206Lead, it is relatively abundant in Earth's crust and is constantly escaping through the crust into the atmosphere. This being the case, it is impossible to attribute all the helium in rock samples to a single decay sequence. The helium found in the rock RATE tested results from many different decay processes, so to attribute it to a single decay process is faulty.

While the RATE project can be commended for trying to use scientific methods for proving a young Earth, there are too many questions regarding its execution and too much ability for a false date to be calculated from the Helium amounts in the rock samples. Excess Helium in rocks may be a genuine mystery, but all possible explanations must be investigated before a true understanding can emerge. The RATE team has jumped the gun by preparing a radical model like accelerated decay, which would have a wide variety of serious consequences that have not been considered.

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