Argon argon dating range
The principal materials for dating East Africa hominid sites are volcanic ashes, yet many of these ashes are not deposited as primary air fall (Greek for ash).
Prior to 1905 the best and most accepted age of the Earth was that proposed by Lord Kelvin based on the amount of time necessary for the Earth to cool to its present temperature from a completely liquid state.
Such numerical calibrations are crucial to understanding rates and timing of evolutionary change.
K-Ar dating has played a key role in unraveling the temporal patterns of hominid evolution as far back as the first significant discovery of East African australopithecines at Olduvai Gorge in 1959.
The Potassium 39 in the sample is irradiated to become Argon 39, then the ratio of the gas is compared.