The controversial idea that space impacts may have wiped out woolly mammoths and early human settlers in North America has received new impetus. Nano-diamonds and other exotic impact materials have been unearthed in thin sediments, Science magazine reports.

The age of these materials coincides with the start of a millennium-long climate cooling event known as the Younger Dryas – some 13,000 years ago. Many large animals vanish from the archaeological record at this time. It is also the period in Earth history that sees the demise of Clovis culture – the prehistoric civilisation that many regard as the first human occupation of North America…

Doug Kennett doubts the theories of over-hunting, climate change and disease used to account for their extinction. There are not enough Clovis kill sites to suggest that the animals were over-hunted, for example, he said.

The animals’ disappearance coincides with that of Clovis artefacts in the archaeological record 12,900 years ago. Prehistoric Clovis Indians lived broadly across North America for a few hundred years. They were big game hunters, who introduced a sophisticated new Stone Age technology – the fluted spear point, known today as the Clovis Point.

The Paleo-Indians vanish at the onset of the post-Ice Age Younger Dryas, or Big Freeze, that snapped Earth back to near glacial conditions, where it lingered for about 1,200 years. The causes of the woolly mammoth extinction, the collapse of Clovis culture and the onset of the cold snap have long been debated. But only the impact theory accounts for the simultaneous occurrence of all three, said Doug Kennett.