By measuring the C concentration or residual radioactivity of a sample whose age is not known, it is possible to obtain the number of decay events per gram of Carbon.By comparing this with modern levels of activity (1890 wood corrected for decay to 1950 AD) and using the measured half-life it becomes possible to calculate a date for the death of the sample. As a result of atomic bomb usage, C ages of objects younger than 1950.The Potassium-Argon dating method is the measurement of the accumulation of Argon in a mineral.It is based on the occurrence of a small fixed amount of the radioisotope Ar with a half-life of about 1,300 million years.The New Zealand physicist Ernest Rutherford, suggested in 1905 that the exact age of a rock could be measured by means of radioactivity.For the first time he was able to exactly measure the age of a uranium mineral.Willard Libby and his colleague Ernest Anderson showed that collected from sewage works had measurable radiocarbon activity whereas methane produced from petroleum did not.
U-Pb geochronology of is used for determining the age of emplacement of igneous rocks of all compositions, ranging in age from Tertiary to Early Archean.By determining the number of tracks present on a polished surface of a grain and the amount of uranium present in the grain, it is possible to calculate how long it took to produce the number of tracks preserved.As long as the mineral has remained cool, near the earth surface, the tracks will accumulate.This half-life (t 1/2) is the name given to this value which Libby measured at 556830 years. After 10 half-lives, there is a very small amount of radioactive carbon present in a sample.At about 50 000 to 60 000 years, the limit of the technique is reached (beyond this time, other radiometric techniques must be used for dating).
The original atom is referred to as the parent and the following decay products are referred to as the daughter.