Main techniques dating hominids
Over time, potassium-40 changes, or decays, into a different material, called argon-40.
By comparing the ratio of potassium to argon, scientists gauge how long this natural clock has been ticking.
"Relative" dating involves comparing one object to others to build a chronology.
Scientists currently don't have a technique for dating fossils like Lucy directly, but they can assign these fossils relative dates based on the age of layers of volcanic ash found above and below them.
Virchow described it as the skeleton of a diseased Cossack cavalryman.
And even once the antiquity of the remains was established, many scientists refused to accept that Neandertals could be closely related to modern humans, depicting them instead as brutish and apelike.
"Absolute" dating means finding a specific age for an object.
A sample of volcanic ash, for instance, can be given an absolute date of 3.18 million years old.
If during K-Ar analyses these detrital grains are not recognized and eliminated then they can cause the measured ages to be systematically too old.
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).
Rather, most are reworked by stream action and are redeposited into the sedimentary environment.
Even during the time this manuscript was written, new hominid discoveries in Ethiopia and Kenya were announced that trace our earliest ancestors further back into the Pliocene.
The ages assigned to these fossils have been obtained through radiometric dating of volcanic rocks interbedded with the fossiliferous sediments.
Lucy and other members of her species, Australopithecus afarensis, lived between 3.9 and 3.0 million years ago.