Archaeological results from accelerator dating
Within 30,000 years, 98% of the already vanishingly small quantities of carbon-14 in bone is gone.
And carbon-14 molecules from surrounding soil start to seep into the fossils.
Libby earned the 1960 Nobel Prize in Chemistry for his work.
The clock gets less accurate as the samples age, however; cruelly, it begins to fail at one of the most interesting times of human history in Europe.
Charles then moved the family and nine-month-old Tom to New Zealand's rugged south island to start an archaeology department at the University of Otago in Dunedin.
As a teenager, Tom spent summers at Ban Na Di, a study site in northeastern Thailand, where his duties included helping with human excavations and brewing tea for the crew.
Most of the thousands of carbon dates from archaeological sites from the Middle-to-Upper Palaeolithic era are wrong, say scientists, perhaps even as many as 90%.
Tom was born in Cambridge, where his father was based until 1966.
That vision sometimes clashes with other scientists' views, but Higham makes no apologies for his interpretations as long as the dates are solid.
“I want to know the truth” is something he says a lot.
At university, he planned to study geography and glaciology, but switched to archaeology after excelling in an introductory course taught by his father that he had signed up for on a whim. “I got less and less interested in archaeology because it was so subjective and woolly.” The reasons for that woolliness were partly technical and partly historical, dating back to before the Highams' time.
Archaeology before carbon dating relied on two principles: older things are buried beneath younger things, and people with cultural ties make similar-looking objects, such as stone tools. In the early nineteenth century, the Danish historian Rasmus Nyerup wrote that most of early human history was “wrapped in a thick fog”.
Tom didn't originally plan to follow his father's path.