The successive layers of rock represent successive intervals of time.
Everything Worth Knowing About ... Scientific Dating Methods
However, the archaeologist can detect bioturbation and allow for its effects. It is clear that carbon dates lack the accuracy that traditional historians would like to have. By using the accelerator mass spectrometer, possible interference from nitrogen is avoided, since it does not form negative ion beams, and interfering molecules are destroyed by stripping electrons away by operating at several million volts. They include potassium-argon dating, that's useful for rocks overyears old. For all other nuclides, the proportion of the original nuclide to its decay products changes in a predictable way as the original nuclide decays over time. This dating system is called tephrochronology. Archaeology has been the chief beneficiary of radioactive-carbon dating, but late glacial and postglacial chronological studies in geology have also been aided greatly.