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Dr. Jay L. Wile, Exploring Creation with Physical Science (Chelsea, MI: Sheridan Books, Inc., 1999, 2000), pp. 337-340. [Brian Merrill.]

The fact that radioactive isotopes decay at a measurable rate allows scientists to use radioactive decay as a means of dating objects whose age we do not know. This is known as radioactive dating. Although radioactive dating can be accurate under certain circumstances, it is important to note that it has some serious weaknesses as well. As a result, radioactive dating techniques must be viewed rather critically. Despite the fact that some scientists will try to convince you that radioactive dating is an accurate means of determining the age of an object, the scientific facts tell quite a different story.

The best way of examining the strengths and weaknesses of radioactive dating is to examine one of the radioactive dating methods in detail. Since 14C [carbon 14] is probably the best known radioactive dating technique, I will discuss that one. As I have already mentioned, 14C decays by beta decay with a half-life of 5,730 years. It turns out that all living organisms contain a certain amount of 14C, making all living organisms somewhat radioactive.

Interestingly enough, living organisms continually exchange 14C with their surroundings. Human beings, for example, exhale carbon dioxide, some of which contains 14C. In addition, human beings eat other organisms (plant and animal), which contain 14C as well. Finally, as you learned way back in Module #2, part of the air that we inhale is made up of carbon dioxide, some of which contains 14C. Thus, organisms are continually exchanging 14C with their environment. The practical result of all of this exchange is that, at any time when an organism is alive, it contains the same amount of 14C as does the atmosphere around the organism.

This changes when the organism dies, however. At that point, the 14C exchange ceases. Thus, the organism cannot replenish its supply of 14C, and the amount of 14C in the organism begins to decrease. Every 5,730 years, half of the 14C in the organism will decay away. In general, then, organisms that have been dead a long time tend to have less 14C in them as compared to those that have been dead for only a short time.

Now if you think about it, this fact can be used to measure the length of time that an organism has been dead. After all, if we know how much 14C was in an organism when it died, and if we measure the amount of 14C in it now, the difference will be the amount of 14C that has decayed away. Since we know how quickly 14C decays, this can tell us how long the organism has been dead. Pretty simple, right?

Well, it would be simple, if we knew how much 14C was in the organism when it died. The problem is, how do we figure that out? After all, no one was around to measure the amount of 14C in the organism when it died; thus, we must make an assumption about how much 14C would have been measured if someone had been there to measure it. As I have said before, there is nothing wrong with making assumptions in science. The trick is that we have to know our assumptions are accurate.

In the case of 14C dating, scientists assume that, on average, the amount of 14C in the atmosphere has never really changed that much. They assume that the amount of 14C in the atmosphere today is essentially the same as it was 100 years ago, 1,000 years ago, etc. Thus, when the age of a dead organism is being measured with 14C dating, we assume that the amount of 14C it had when it died was the same as the amount of 14C that is in the atmosphere now. That gives us a value for how much 14C was initially in the dead organism. We can measure the amount of 14C that is in the organism now and then determine how long the organism has been dead.

Notice, however, that the age we get from this process is completely dependent on the assumption that we made about how much 14C was in the organism when it died. If that assumption is good, the age we calculate will be accurate. If that assumption is bad, the age we calculate will not be accurate. So the question becomes, "Is the assumption accurate?" In short, the answer is "no."

Through a process involving tree rings, there is a way we can measure the amount of 14C in the atmosphere in years past. When a tree is cut down, the rings in the tree's trunk can be counted to determine how old the tree is [or how many growth cycles it has been through]. Each ring represents a year in the life of the tree. [?] We know which rings corresponds to which year by simply counting the rings from the outside of the trunk to the inside. Well, it turns out that through a rather complicated process, we can actually measure the amount of 14C in a tree ring, and use it to determine how much 14C was in the atmosphere during the year in which the tree ring was grown. As a result, scientists have determined the amount of 14C in the atmosphere throughout a portion of the earth's past.

Scientists have studied the 14C content in tree rings that are as many as 3,000 years old. From these measurements, scientists have determined the amount of 14C in the atmosphere over the past 3,000 years. What they have seen is that the amount of 14C has varied by as much as 70% over 5that time period. The variation is correlated to certain events that occur on the surface of the sun. As a result, we know that the amount of 14C in the atmosphere has not stayed constant. Instead, it has varied greatly. Thus, we know that the initial assumption of 14C dating is wrong. Thus, one must take most 14C dates with a grain of salt. After all, we know that the assumption used in making those dates is wrong. Consequently, we cannot up too much trust in the results!

Notice that I said we must take "most" 14C dates with a grain of salt. Why "most"? Why not "all"? It turns out that since we can determine the amount of 14C in the atmosphere during the past using tree rings, we can actually use that data to help us make our initial assumption. As a result, the assumption becomes much more accurate. The problem is, however, that we don't have 14C measurements for tree rings older than 3,000 years. Thus, we can only make an accurate assumptions [sic] for organisms that have died within the last 3,000 years. As long as the organism died in that time range, we can use tree ring data to help us make an accurate assumption of how much 14C was in the organism when it died. For organisms that have died longer than 3,000 years ago, we have no tree ring data, so we have no way to make an accurate assumption. As a result, we cannot really believe the 14C date.

In the end, the, the 14C dating method can be believed for organisms that have been dead for 3,000 years or less. Thus, it is a great tool for archaeology. If an archaeologist finds a manuscript or a piece of cloth (both cloth and paper are made from dead plants), the archaeologist can use 14C dating to determine its age. As long as the result is about 3,000 years or younger, the date can be believed. If the date turn out to be older than 3,000 years, it is most likely wrong.

So you should see that radioactive dating involves a pretty important assumption. If the assumption is good, the date obtained from radioactive dating is good. If the assumption is bad, the result obtained from radioactive dating will be bad. Now there are a lot of other radioactive dating techniques besides 14C dating. Unfortunately, they all suffer from a similar malady. In every radioactive dating technique, we must make assumptions about how much of a certain substance was in the object originally. Such assumptions are quite hard to make accurately.

The difficulty of making these assumptions can be seen in the fact that radioactive dates have been demonstrated to be wrong in many, many instances. John Woodmorappe, in his book Studies in Flood Geology, has compiled more the 350 radioactive dates that conflict with one another or with other generally accepted dates. These erroneous dates demonstrate that the assumptions used in radioactive dating cannot be trusted. As a result, the dates that one gets from radioactive dating cannot be trusted, either.

Unfortunately, many in the scientific community are unwilling to admit to the inadequacies of radioactive dating because many scientists like its results. Because certain radioactive decay schemes have long, long half-lives, the dates that one calculates from these methods can be breathtakingly large. For example, there are rocks on the planet that radioactive dating techniques indicate are more than 4 billion years old. It turns out that many scientists want the earth to be that old because they believe in the discredited hypothesis of evolution. This hypothesis requires a very old earth, and radioactive dating techniques provide dates that indicate the earth is very old. As a result, they turn a blind eye to the inadequacies of radioactive dating because it gives them an answer that they want! Hopefully, as time goes on, this unfortunate situation will change!