Archaeologists dating methods

Another promising site is a South African cave called Swartkrans, where archaeologists in the ’80s found burned bones in a section dating between 1 million and 1.5 million years ago.

In 2004, Williams College chemist Anne Skinner analyzed the bones using electron spin resonance, which estimates the temperature to which an artifact has been heated by measuring molecular fragments called free radicals.

The “eureka” moment came later, as the slices were examined under a microscope at Israel’s Weizmann Institute. The bones’ sharp edges, and the excellent preservation of the plant ash, indicated that neither wind nor rain had ushered in the burnt material. Then team member Francesco Berna subjected the sample to a test called Fourier transform infrared microspectroscopy (FTIR), which analyzes a material’s composition by measuring the way it absorbs infrared waves.

Often used in crime labs to identify traces of drugs and fibers, FTIR can also determine the temperature to which organic matter has been heated — and Berna is among the first to adapt it for archaeology.

At the base of a brush-covered hill in South Africa’s Northern Cape province, a massive stone outcropping marks the entrance to one of humanity’s oldest known dwelling places.

Humans and our apelike ancestors have lived in Wonderwerk Cave for 2 million years — most recently in the early 1900s, when a farm couple and their 14 children called it home.

Until the Wonderwerk Cave find, Gesher Benot Ya’aqov, a lakeside site in Israel, was considered to have the oldest generally accepted evidence of human-controlled fire.

Firelight could ward off nighttime predators, allowing hominins to sleep on the ground, or in caves, instead of in trees.No longer needing huge choppers, heavy-duty guts or a branch swinger’s arms and shoulders, they could instead grow mega-craniums.The altered anatomy of , Wrangham wrote, indicates that these beings, like us, were “creatures of flame.” There was one major problem with this hypothesis, however: Proving it would require evidence of controlled fire from at least 1.8 million years ago, when the first appeared.The Cooking Hypothesis When the team announced its findings in April 2012, it added fuel to a controversy that’s been smoldering since 1999.That year, influential primatologist Richard Wrangham proposed a theory of human origins called the “cooking hypothesis.” Wrangham aimed to fill a gap in the story of how early hominins like Australopithecus — essentially, apes that walked upright — evolved into modern Homo sapiens.

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