The most commonly used chronometic method is radiocarbon analysis.
It measures the decay of radioactive carbon (14C) that has been absorbed from the atmosphere by a plant or animal prior to its death.
But, even when the scientific methods of absolute dating are available, this method of dating has not lost its importance, as many a time we have to depend solely on relative dating.
Even when the absolute dates are available, we have to supplement the information with relative dating.
This number is usually written as a range, with plus or minus 40 years (1 standard deviation of error) and the theoretical absolute limit of this method is 80,000 years ago, although the practical limit is close to 50,000 years ago.
The earliest-known hominids in East Africa are often found in very specific stratigraphic contexts that have implications for their relative dating.This also works with stone tools which are found abundantly at different sites and across long periods of time.Stratigraphic dating is based on the principle of depositional superposition of layers of sediments called strata.The most common relative dating method is stratigraphy.Other methods include fluorine dating, nitrogen dating, association with bones of extinct fauna, association with certain pollen profiles, association with geological features such as beaches, terraces and river meanders, and the establishment of cultural seriations.They do not, however, give "absolute" dates because they merely provide a statistical probability that a given date falls within a certain range of age expressed in years.Chronometric methods include radiocarbon, potassium-argon, fission-track, and thermoluminescence.But, for a single culture site the method is quite reliable.Quite convincing dates are sometimes arrived at by importing parallels from other contemporaneous cultures.Cultural seriations are based on typologies, in which artifacts that are numerous across a wide variety of sites and over time, like pottery or stone tools.If archaeologists know how pottery styles, glazes, and techniques have changed over time they can date sites based on the ratio of different kinds of pottery.