Radioactivity and The Age of the Earth
An introduction to radioactive decay and the assumptions of radiometric dating methods.
Taken from the September 2004 Creation Answers Newsletter.
by Wayne Spencer
Radioactive Decay is a term referring to a variety of processes in which the nucleus of an atom changes. These changes are spontaneous and random, for any given atom. That means an atom that can decay can change at any time and there is no way to predict when. But, for a sample that we can measure in a laboratory (which has many many atoms in it), the overall rate that the radioactive atoms change is known from experimental measurements. How the atom changes is something that can be determined and measured very precisely.
Radioactive age dating techniques begin with very carefully separating the radioactive elements from the sample. Then the concentrations of several isotopes related to the decay process are measured very precisely. (Isotopes are different forms of the same element, such as Carbon-12 and Carbon-14. The numbers 12 and 14 in this notation are the total of the number of protons plus the number of neutrons in the nucleus of the atom. Isotopes have the same number of protons but vary in how many neutrons they posses in the nucleus.) After the amounts of the various isotopes are determined a mathematical extrapolation is made that gives an age figure for the sample. The age is determined based on the assumption that radioactive elements would have decayed at the same rates in the past as they do in the present, when studied in today’s laboratories.
Most radioactive decay involves one of four processes: 1) alpha decay, 2) beta decay, 3) electron capture, or 4) positron emission. In alpha decay, the atomic nucleus gives off what is called an alpha particle, which consists of two protons and two neutrons. An atomic nucleus is essentially Helium without its electrons, so it quickly turns into Helium as it picks up electrons from other atoms. In beta decay, one of the neutrons in the nucleus comes apart, and this ejects an electron out of the nucleus. In the process, the nucleus gains one proton from the neutron that came apart. In electron capture, an electron orbiting the nucleus gets “captured” by the nucleus. In positron emission, the nucleus ejects a positron, which is a small particle like an electron except that it is charged positively and it spins opposite an electron. Positron emission involves a proton being changed into a neutron, a positron, and a neutrino.
Radioactive decay can be harmful to living things because the charged particles given off by the radioactive material ionizes matter and can cause chemicals in the body to break down. All matter has a small proportion of radioactive atoms in it. The energy given off by the charged particles and the concentration of the radioactive substances determine how dangerous they are to living things.
To give one example of a radioactive “clock,” let us look at Potassium-Argon decay (or K-Ar decay using symbols from the Periodic table). This process is used frequently in dating basalt rock, from lava flows. Potassium exists in three isotopes, K-39, K-41, and K-40. It turns out that 93% of Potassium is K-39, 7% of it is K-41, and these isotopes are both stable, so they do not undergo radioactive decay. But, a small percentage, 0.0117% of Potassium is K-40. K-40 decays by three different processes, beta decay, positron emission, and electron capture. The last two of these produce Argon-40. This is what is referred to in Potassium-Argon dating (or K-Ar dating). In this process, Potassium-40 is referred to as the parent isotope and Argon-40 is referred to as the daughter isotope.
In the case of Potassium-40 decay, the half-life of K-40 is 1.25 billion years. The half-life is not an age figure, though it is measured in years. The half-life is the time for half of the Potassium-40 atoms to break down into Argon-40 and the other particles that come from the process. No matter how much of it there is, it will take 1.25 billion years for half of the K-40 atoms to decay. This means that the decay process is very slow for K-40. K-Ar dating is often used in dating lava flows. There are a number of radioactive isotopes used to date rocks. These include Uranium-Lead, Samarium-Neodymium, Rubidium-Strontium, as well as Potassium-Argon.
There are some important questions to ask about radioactive dating methods. Geologists and planetary scientists take radioactive dating techniques as reliable and accurate. They are also understood to give confirmation that Earth’s rocks are millions and billions of years old. Note that assuming evolution, the age of the Earth and solar system is believed to be 4.6 billion years. To understand what is reliable and what is not reliable about these dating techniques, we must ask the following questions:
1) Are the assumptions valid?
2) Are the equations and theories correct?
3) Are the laboratory procedures adequate?
4) Are the results reliable?
Constant Decay Rate
First of all, we will consider the assumptions of radioactive (or radiometric) dating. A primary assumption is that the decay rate is a never-varying constant for each radioactive isotope. This is widely believed because the decay rate can be measured with great precision and it is very repeatable. There have been attempts to cause the decay rate to vary in laboratory experiments. Experiments have been able to show minor variations in the decay rate of some isotopes. But as a rule, the decay rate is very constant and predictable. Recent Research from a team of creationist scientists is beginning to call this assumption into question, however. This research effort is known as RATE, which is an acronym which stands for Radioactivity and the Age of The Earth.
Unusual times in history such as the Creation week and the time of Noah’s Flood may have involved accelerated radioactive decay. Though I have felt reluctant to accept this idea, I am now becoming more open to it as a result of the recent research results. More will be said about accelerated decay in future newsletters. Though in laboratory measurements we find radioactive decay rates constant, there now appears to be evidence suggesting they were not constant at all times in the past. This new evidence may be very helpful in reconciling many facts with a Biblical view of history.
The second major assumption of radioactive dating techniques is that the materials undergoing radioactive decay are a closed system. This means that to do the age calculation you assume no natural processes other than radioactivity was occurring that would throw off the calculation. To understand how this is a problem, imagine a large hour glass with sand in it. Say that you turn over an hour glass to start the sand running down to the bottom, then leave the room. When you come back, you see half of the sand in the top and half in the bottom so you assume that one-half hour has passed (assuming we have a true 1-hour hour glass). But what if someone you didn’t see came in while you were out of the room and they took the top off of the hour glass and took some sand out of the top, then placed the top back on before you came back in? This would make it look like more time had gone by than had actually transpired. You might see the top part of the hour glass and think more time had gone by than was actually the case.
This illustration is similar to what happens sometimes with radioactive dating techniques. It turns out that there are a variety of geological processes that can remove some of the parent isotope or add to the daughter, thus making the age results too large. Note that geologists are very careful about where they get samples for radioactive dating analysis. Some types of rock formations would never be dated with radiometric dating techniques because geologists know they would not get meaningful results. The problems come when there are geological processes affecting the samples that are not known or are not accounted for in the age calculation. For instance, in the decay of Uranium to Lead, the Uranium mineral can dissolve in water (from rain or ground water) and so rain can remove some of the parent isotopes, making the rock age come out too large. Though it also is possible for processes to make the age results too small, that problem appears to be easier to detect and relatively unusual. Another example is in K-Ar decay. Argon gas is often trapped in molten rock that comes up from the Earth’s mantle. This gas can throw off K-Ar age calculations since Argon from the mantle is a nonradioactive source of an element that would be assumed to only come from radioactive decay. Creationist geologist Andrew Snelling has written technical papers demonstrating this.
I believe that the assumption of a closed system is the biggest problem with radioactive dating methods. Though scientists are aware of many processes that can interfere with the results, there are still others that creationist research is elucidating. Assuming an old age for Earth (and the planets) sometimes leads scientists to fail to look for certain types of processes. Young age creationist scientists are bringing new perspectives to the research and are discovering very surprising things. I think this greatly strengthens the case for a young Earth and solar system.
Initial Concentrations Known
Radioactive dating calculations have to make some assumptions about the initial concentrations of the radioactive isotopes that are being studied (such as the parent and daughter). This has to do with when the radioactive “clock” started. For instance, the time when a rock hardened containing radioactive Potassium would be the start of the age “clock” for K-Ar decay. This problem also becomes important in dating organic materials from living things with Carbon dating. In a Biblical view of history, there was a world-wide Flood. Noah’s Flood drastically reduced the amount of carbon in the Earth that was found in living things due to all the living things that died in the Flood (plant and animal). This and other effects would drastically change the concentration of radioactive Carbon-14 on the Earth in Noah’s Flood. This has led scientist John Baumgardner to calculate a young age for the Earth and in the process show how Carbon-14 ages can be corrected. (See the June 2004 issue of this newsletter for more on Carbon-14 dating.)
The assumptions inherent in radioactive dating methods are sources of systematic error that lead to age calculation results that are too large. The second question to ask about radiometric methods is “Are the equations and theories correct?” I do not feel there is any significant problem with our understanding of the physics of radioactive processes. There is some controversy among physicists about why radioactive decay occurs in the first place. This is something we don’t really know, but we do know how to describe how it happens, and we know what the effects of it are. As Christians we should respect the good science even in this subject, even though some inconsistent and inaccurate results are obtained from it.
The third question to ask is about the laboratory procedures. Are they adequate to provide valid results? I think they are, as long as the results are interpreted properly. In the past there have been claims by some who worked in radioactive dating laboratories that there were improprieties in what age results were published. Some have claimed that though actual age results obtained varied over a wide range of ages, only the ages that were believed to be correct from old age assumptions were published. There are times when the pressure to publish values accepted by the scientific community has probably outweighed proper procedure, though I have found it difficult to find real documentation of these claims.
On the other hand, the chemical and other processing procedures in radiometric dating laboratories has been much refined over the years. The experimental procedures in this work are extremely precise. So, I think we should have a degree of respect for the careful work in these laboratories. In the laboratories, it is actually ratios of concentrations of the various isotopes that is measured. Then the age is calculated, based on certain assumptions. Rather than just dismissing these age results, we should bring a new approach that explains the data better. I believe creationists are beginning to accomplish this.
The fourth question to ask about radioactive dating is “Are the results reliable?” This can be viewed from several different angles. In some cases, the dates from the radiometric age completely contradicts what is known from historical information or what is known from the geological setting. Creationists have documented some dramatic examples of this in the Grand Canyon, for instance. In other cases, when multiple radioactive dating methods are used on the same samples, using different isotopes, the results can be totally inconsistent.
Over the years young age creationists have documented many examples of radioactive methods giving inconsistent results. On the other hand, it is also true that there are cases where three or four radioactive methods all agree with each other very well. Note that four radiometric dates can agree and all be wrong if there is a systematic error that affects them all.
Evolutionist scientists and geologists have long challenged young age creationists by bringing up many technical issues related to radioactive dating methods. Though there has long been reason to question radioactive dating results, creationists are now coming to new answers that are exciting for Christians. The young age point of view is often seen as irrational and those who believe it are considered ignorant by people in the sciences. It is time for Christians to become more aware of the excellent research from young age creationists on this important topic. This research is confirming a Biblical view of history, making the Earth about 6 to 8 thousand years old. Future newsletters will have more on radioactive dating methods.
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