A portion of the carbon is the radioactive isotope carbon-14.
At death, the exchange stops, and the carbon-14 then decays with a known half-life, which enables scientists to calculate the time of death.
‘Dating is absolutely crucial, it underpins everything,’ says Michael Walker.
Based at the University of Wales Trinity St David, he has devoted his career to studying the Quaternary period – the last 2.6 million years and the so-called ‘age of humans’.
It was developed right after World War II by Willard F.
Familiar to us as the black substance in charred wood, as diamonds, and the graphite in “lead” pencils, carbon comes in several forms, or isotopes.
One rare form has atoms that are 14 times as heavy as hydrogen atoms: carbon-14, or C ratio gets smaller.
Working with several collaboraters, Libby established the natural occurrence of radiocarbon by detecting its radioactivity in methane from the Baltimore sewer.
In contrast, methane made from petroleum products had no measurable radioactivity.