Tree 'marks onset of Anthropocene Epoch'

A remote spruce planted on Campbell Island in the Southern Ocean holds a defining record of humans, scientists argue. Chris Turney, from the University of New South Wales, Australia, and colleagues, say the tree's wood contains a sharp peak in radiocarbon, the result of the A-bomb tests in the 1950s and 1960s. As such, it could be used to define the onset of a new geological age known as the Anthropocene Epoch. Prof Turney has been speaking to our science correspondent Jonathan Amos.