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Radiometric Dating

Unstable atomic isotopes of an element have a nucleus that will spontaneously change to another element, called a daughter element, releasing radiation. This decay happens at a set rate, at any given moment there is a set probability that the nucleus will decay into daughter elements. For example, Carbon-14 decays into stable Nitrogen-14. The half-life, or amount of time for half of a sample to decay, of 14C is about 5700 years.

Radioactive decay using 14C is used to date samples organic material with a limit to about 50,000 years and other radioactive elements are used to date samples of rock with years ranging from about 200,000 years to hundreds of millions of years. Many Christian creationists feel the Bible indicates the Earth was created no later than 10,000 years ago, so radiometric dating poses a potential problem. The dates are typically consistent, so that deeper down rocks are generally given older dates than rocks higher up in the earth. However, radiometric dating is more complicated than using the simple exponential decay formula. For radiometric dating, there are some assumptions that are used and adjustments are made because of these assumptions.

  1. The amount of daughter elements of the original sample is known.
  2. None of the radioactive element or the daughter element has been added to, or taken away from, the sample.
  3. The decay rate has not changed since the sample was formed.

Let us look at each assumption more closely.

  1. For some types of radioactive dating, scientists claim that the amount of the daughter element in the sample is known to be zero such as in Potassium-Argon dating of volcanic rock. However, it has been shown that some Argon can become trapped in the rock when it is formed, thus making the dating wrong (link retrieved 2017). For Carbon-14 dating, the amount of 14C is not really known. Carbon-14 enters organic material when plants absorb carbon dioxide from the atmosphere when they photosynthesize, and animals get the 14C from eating the plants. As long as the plant or animal is alive it will maintain the same ratio of Carbon-12 to Carbon-14 as is in the atmosphere, but when it dies, it takes in no more carbon. The 14C decays and the ratio increases. The problem is that the amount of 14C in the atmosphere has not been constant. As humans burned more and more fossil fuels, the amount of carbon dioxide in the atmosphere has increased. So to try to account for this, scientists have dated historical artifacts with known dates to create a calibration curve for Carbon-14 dating. This calibration curve is also sometimes created using tree-ring data, but the dates of the tree rings are sometimes found through Carbon-14 dating which leads to circular logic.

  2. The second assumption is that no radioactive or daughter elements have been added to or taken away from the sample. Going back to the Potassium-Argon dating method, pressure can force excess argon into solid rock and pre-formed crystals. This led to dating issues in the Alps (link retrieved 2017)

  3. The third assumption is that the decay rates stay constant. While this seems to be true, there are small slight variations probably due neutrinos emitted by the sun (link retrieved 2017). These variation are so small that they should not affect the dating methods, but what if the decay rates were different in the past. Also consider that in the right conditions radioactive decay can happen very quickly such as in a nuclear reactor.

There are other things to consider with radiometric dating.

  1. The dating methods are calibrated with other methods. These are in turn, fixed to the age of the earth and rocks as developed by geologists before radiometric dating was developed. (link retrieved 2017).
  2. Different dating methods can give different dates for the same set of samples (link retrieved 2017).
  3. Soft tissues, proteins, and DNA have been found in dinosaur fossils. Proteins and DNA have decay rates similar to radioactive isotopes and studies have shown that there should not be any detectable DNA after about 100,000 years (or 6.4 million years under ideal conditions) (link retrieved 2017). Nevertheless, some scientists claim to have found dinosaur DNA (link). Also, Carbon-14 dating can only measure to about 50,000 years ago (link), but has been found in fossils (link retrieved 2017) indicating they are not millions of years old.

Radiometric and radiocarbon dating is a controversial subject. Secular scientists would like everyone to believe it is a foolproof method with no substantial problems. Carbon-14 dating does seem to work well for the historical time period where the method has been calibrated using historical artifacts. Before that is extrapolation which may or may not be accurate. Creation scientists would like to point out the shortcomings and possible issues with the methods because each person should understand both sides of the issue and encourage further open-minded research.

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