Many rocks and organisms contain radioactive isotopes, such as U235 and C14. These radioactive isotopes are unstable, decaying over time at a predictable rate. The latest hightech equipment permits reliable results to be obtained even with microscopic samples. Radiometric dating is selfchecking, because the data (after certain preliminary calculations are made) are fitted to a straight line (an "isochron") by means of standard linear regression methods of statistics. Halflife is the amount of time it takes for half of the parent isotopes to decay. In another 5,730 years, the organism will lose another half of the remaining C14 isotopes. This process continues over time, with the organism losing half of the remaining C14 isotopes each 5,730 years. Familiar to us as the black substance in charred wood, as diamonds, and the graphite in “lead” pencils, carbon comes in several forms, or isotopes.
