To understand radioactive dating, a person must have some knowledge of chemistry, which is the study of the structure and properties of matter. Matter is made up of elements (pure substances, of which there are slightly over one hundred), compounds (chemical combinations of the elements) and mixtures of the above. The atomic theory describes the atom as the smallest particle of an element that still has the property of that element. An atom consists of electrons and a nucleus made up of protons and neutrons. For example, an ordinary carbon atom has six protons, six neutrons and six electrons. It is known as carbon-12 because the sum of the protons and neutrons equals twelve. Elements can have isotopes, which are atoms with the same number of protons but a different number of neutrons. Carbon, for example, has another isotope known as carbon-14 because it has six protons and eight neutrons. A radioactive isotope is one that is not stable and decays by giving off some form of radiation. Carbon-14 is a radioactive isotope.
The radiocarbon dating method utilizes the fact that, in the upper atmsphere, cosmic rays react with nitrogen to from carbon-14. Also, in the upper atmosphere, carbon reacts with oxygen to form carbon dioxide. Thus, some carbon dioxide contains carbon-12 and some contains carbon 14. Plants and, indirectly, animals ingest this radioactive carbon dioxide along with normal carbon dioxide. Carbon-14 decays to carbon-12. The time for which carbon-14, which is estimated to be 5,760 (plus or minus 30) years. The longer the plant or animal has been dead, the less will be the ratio of carbon-14 to carbon-12. If one analyzes the amount of radioactive substance in a sample and compares it to the amount of radioactive substance it originally was assumed to have, one can attempt to calculate the age of the substance using the half-life.
1. One must assume knowledge of the original amount of both the radioactive isotope and the decay produt. The ratio of carbon-14 to carbon-12 for carbon dioxide is not yet in equilibrium. Who knows what the ratio of carbon-14 to carbon-12 was thousands of years ago? The cosmic ray influx would have had to remain constant in order to estimate the amount of carbon-14 originally present. In the uranium-lead dating method, it is assumed that there was no lead in the original sample.
2. Changes in these concentrations can only occur by radioactive decay, i.e., none of these changes can occur by leaching or any other process but radioactive decay. Could not some of the substance be washed in or out by the liquids in the soil or decomposed due to other factors? As much as 90% of the total radioactive elements of some granites could be removed by leaching the granulated rock with weak acid.
3. The ratio of decay is constant regardless of external conditions. Who knows that the rate of decay has remained constant over thousands of years? Could teperature, pressure and other factors have affected this raate?
Carbon dating often arrives at dates much different from those determined by archaelolgical studies or other methods. For example:
1. Shells of snails living in southern Nevada gave an apparent age of 27,000 years.
2. A shell from a live clam was dated thousands of years old.
3. Dried seal carcasses less than 30 years old were dated as old as 4,600 years, and a freshly-killed seal was dated at 1,300 years old.
The potassium-argon radiometric dating method was used on some volcanic rocks off Hualalai in the Pacific Islands of Hawaii. These rocks were erroneously dated as being 160 million and 3 billion years old. Actually, these rocks were formed during a volcanic eruption in the year 1801. Also, radiometric dating methods used on volcanic rock on Reunion Island in the Indian Ocean gave results varying from 100,000 to 4.4 billion years.
Thus we can conclude that dates obtained by radiometric methods are interesting geo-physical exercises, but they do not provide accurate information as far as the age of the earth is concerned.