

Among the bestknown techniques are radiocarbon dating, potassiumargon dating and uraniumlead dating.By allowing the establishment of geological timescales, it provides a significant source of information about the ages of fossils and the deduced rates of evolutionary change.Prior to 1905 the best and most accepted age of the Earth was that proposed by Lord Kelvin based on the amount of time necessary for the Earth to cool to its present temperature from a completely liquid state.Although we now recognize lots of problems with that calculation, the age of 25 my was accepted by most physicists, but considered too short by most geologists. Recognition that radioactive decay of atoms occurs in the Earth was important in two respects: Principles of Radiometric Dating Radioactive decay is described in terms of the probability that a constituent particle of the nucleus of an atom will escape through the potential (Energy) barrier which bonds them to the nucleus.The Half Life Time is the amount of time it takes for half of the atoms in a sample to decay.Half Life is a characteristic of each radioactive isotope.To see how we actually use this information to date rocks, consider the following: Usually, we know the amount, N, of an isotope present today, and the amount of a daughter element produced by decay, D*.


Together with stratigraphic principles, radiometric dating methods are used in geochronology to establish the geological time scale. Thus, if we start out with 1 gram of the parent isotope, after the passage of 1 halflife there will be 0.5 gram of the parent isotope left. After the passage of two halflives only 0.25 gram will remain, and after 3 half lives only 0.125 will remain etc. Radiometric dating is also used to date archaeological materials, including ancient artifacts. Different methods of radiometric dating vary in the timescale over which they are accurate and the materials to which they can be applied.
