Radioisotope Dating and Circular Logic

Circular logic

Trying to prove that the earth is extremely old

by Curt Sewell

Circular logic is a logical error, caused by first making some assumption that can’t be proven true, then, on the basis of that assumption, deriving some result that is then used to “prove” that the first assumption is true.

We’ll see that radiogenic dating, used to try to prove that the earth is extremely old, is a prime example of circular logic. It’s often quoted as being an accurate measurement, but we’ll show that many errors are quietly discarded, and blamed on some unknown contamination in the rock sample that was measured.

The process (as used by secular scientists) goes something like this:

1) Assume that the early parts of the Bible are not literally true.

2) Therefore, God didn’t really create the world and its inhabitants in only six days.

3) Thus, we can try to find a way to explain the world without relying on a supernatural cause.

4) Now assume that the world developed slowly, by natural processes similar to those we see working today. This is called the theory of uniformitarianism.

5) It’s obvious that this would take a long time, but how do we prove how long that would take?

Notice that points #1 and #4 contain assumptions that we can’t prove. But let’s go on and see what happens if we “temporarily” assume that they’re both true.

6) We know that certain radioactive metals have extremely long half-life (that is, they decay very slowly). Maybe they could be used to show that the earth is very old.

7) When these metals decay (at a rate determined by their long half-life) they are transformed into other kinds of metals. For example, Uranium-238 changes into Lead-206. This reaction has a 4.55-billion-year half-life.

8) Therefore, if a certain mineral contains both Uranium-238 and Lead-206, and if we assume that most of the Lead-206 was derived radiogenically, the ratio of these two isotopes should allow an estimate of the fraction of Uranium-238 that had decayed, and since we know the half-life of Uranium-238, we can therefore find how long it took for this process to take place.

Notice another assumption in point #8 –no one can prove that one either.

9) If all of these steps are correct, then we can show an ancient age for many rocks. After many such rocks are dated, if they seem to agree with each other, we can say the earth must be older than they are, and come up with an estimate of the earth’s age. The current guess is some 4-1/2 billion years.

10) This line of reasoning is used by the majority of scientists to “prove” that God didn’t create the earth in a very short time (the Bible says six days), since this “proves” that the earth is very ancient.

Now, what’s wrong with this picture? It sounds reasonable, if all of the assumptions in all of the above steps are true and correct. But suppose that steps 1) and 2) are bad assumptions, and that God really did create the world in a very short time, as the Bible says (in many places other than just early Genesis). Suppose that, in step 8), the Lead-206 got there some other way than by radioactive decay. Is there anything in the above process that could adequately contradict these suppositions? Not at all! Here’s a good example of circular logic.

Let’s look at some actual scientific evidences and see how they apply to the above discussion. Radiogenic dating is not the primary way that paleontologists determine the date of most fossils. It can’t always be used, because the material surrounding the fossil often doesn’t contain the right isotopes, and the measurement for radiogenic dates is destructive and thus the fossil itself can’t be dated. Usually there are other fossils located nearby, and often these have been determined to be index fossils — that is, fossils of creatures that only lived during certain times of earth history before they became extinct. But this process also involves a number of assumptions, including the assumption of an evolutionary development of those creatures! …


image credit: Yiran Ding