So how do we investigate the development of human evolution if it’s outside the radiocarbon timescale?
To get a clearer picture, scientists are exploiting diverse physical phenomena, from uranium’s radioactivity to life’s preference for l-amino acids.
Yet cave paintings are generally considered to be physical traces of early modern behaviour, because the creation of art requires abstract thought. ‘The reason we started to look at dating cave art was because we had this slight conundrum,’ says Alistair Pike, an archaeologist at the University of Southampton in the UK.
‘When we look at genetics, they suggest that modern humans become anatomically modern between 150,000 and 200,000 years ago in Africa.
well, us.‘The great breakthrough in Quaternary archaeology was radiocarbon dating,’ Walker says.
Developed by Willard Libby in the 1940s – and winning him the Nobel prize in chemistry in 1960 – the basic principle of radiocarbon dating is simple: living things exchange carbon with their environment until they die.
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’.
The first excavations in the 1950s and 1960s revealed a hub of ancient human activity, spanning thousands of years’ worth of artefacts.
Unfortunately much of it originates from outside radiocarbon dating’s timescale. was almost non-existent,’ says Geoff Duller, a geochronologist from the University of Aberystwyth in Wales.
[but] if you haven’t got organic pigment in there, you can’t use radiocarbon and you’d be destroying the art, which is very valuable.
To take a normal radiocarbon sample would be unduly disruptive,’ he explains.