Radioactive Dating Techniques


The dating of fossils and rocks using radioactive dating techniques is considered by most to be a very reliable ‘scientific’ method. It is almost universally accepted that these procedures attribute an absolute date to rocks and therefore also to the fossils found within the rock. This results in the belief that the earth is billions of years old. The best known of these techniques is radiocarbon testing (or carbon dating). Other methods used are known as potassium-argon, rubidium-strontium and uranium-thorium-lead testing.

Radioactive substances are unstable. They decay to form new substances at a particular rate. The rate of decay is measured in terms of a ‘half life’ which is the time taken for half the amount of the original (parent) substance to become the new (daughter) substance. If you knew how much of the parent element you had to start with, the remaining amount of parent element and the known decay rate would indicate how much time had elapsed in the decay process.

Radiocarbon dating, for example, is based upon C14 (carbon) decaying to C12. Living organisms have a set C14 to C12 ratio. Scientists use this to determine how much C14 was present in the living organism. When the animal dies, C14 decays to C12 with a relatively short half life. By analysing the remains of living matter, one can make an estimate as to how long ago the organism lived.

Radiocarbon testing has proven to be quite unreliable. Scientists have observed large errors when dating something they already knew the age of. This is largely due to the fact that the object being tested was not in a closed system. Through time, carbon was added or taken away by environmental interference. The short half life of radiocarbon is also only suitable for testing fossils or other dead matter no more than a few thousand years old. It is therefore never used to determine the age of fossils in the geological column as they are considered to be millions of years old. Interestingly though, fossils submitted for radiocarbon testing yield results and fix their ages at only a few thousand years.

Other radioactive dating techniques have longer decay rates and are therefore more suitable for dating objects older than a few thousand years. The elements used in these tests are inorganic. You therefore do not know how much of the parent element you had to start with. The assumptions you need to make to use these methods are:

1. how much parent element there was originally.

2. a  constant decay rate throughout time.

3. a closed system.

Carbon dating has already shown that 2. and/or 3. are not valid assumptions.

"Thus the assumption of immense ages has not been proven."1

Yet radiocarbon dating is still used and purported as scientific proof of the earth’s magnificent age.

1. An evolutionary geologist (Dr Y.F. Zheng) recently wrote a paper in the international journal Chemical Geology to collate the claims of various mathematical techniques used to try and remove the problem of unknown initial conditions in radioactive dating. His conclusions were uncomplimentary. This is one of his quotable quotes.

Becky Conolly

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