Main techniques dating hominids
The Laetoli footprints are rare treasures in the record of human ancestry.
They are fossils captured in volcanic rock that can be given an absolute date.
In the past two decades, particularly, discoveries of our fossil ancestors have been made in unprecedented numbers and diversity.
Detailed studies of these fossils provide new insights into human evolution, such as the origin of locomotion and cultural activity, and the evolution of the brain, among many other complex features that have come to define humanity.
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.
Volcanic rock -- like the trail at Laetoli -- can be dated by a method called potassium-argon dating.
Hot, newly erupted lava and ash contain a form of the chemical element potassium (called potassium-40) that is radioactive.
Rather, most are reworked by stream action and are redeposited into the sedimentary environment.This interpretation reflected the prevailing prejudices about human ancestry, and was supported by misinterpretation of the remains of the "Old Man of La Chapelle", whose skeleton was warped by arthritis.Even when the idea that apes and humans shared a common ancestor became more widely accepted, the concept of an African origin was not.Now we know, through a combination of new fossil finds and molecular biology, that humans and chimpanzees diverged as little as 7 million years ago, and that our own lineage is "bushy", with many different species in existence at the same time.Our view of our evolutionary past has changed as social attitudes have changed.