地质年代是指地壳上不同年代的岩石在形成过程中的时间和顺序。测定化石的地质年代,现在主要用放射性同位素的方法。放射性同位素以自己恒定的速度进行衰变,不受外界温度和压力的影响,跟它是以单质存在或以化合物状态存在都没有关系。它遵循一定的规律,即指数衰变规律。假如某种放射性同位素最初共有N_0个原子,经过时间i以后,只剩下N个,则N和N_0之间的关系为: Geological age refers to the time and sequence of rock formation in different ages on the Earth’s crust. The geochemical age of fossils has been measured, and radioisotope methods are now mainly used. The radioisotope decays at its own constant rate and is not affected by outside temperatures and pressures. It does not matter whether it exists as a simple substance or exists as a compound. It follows a certain law, that is, exponential decay. If a radioactive isotope initially has N_0 atoms, after the time i has elapsed, there are only N, then the relationship between N and N_0 is: