A team of U.S. scientists that has unearthed a layer of microscopic diamonds on a California island (USA) is calling the find a possible 'smoking gun' to prove a controversial theory that debris from a massive comet - believed to have smashed into northern Canada nearly 13,000 years ago - wiped out the woolly mammoth and dozens of other Ice Age mammals, triggered a 1,000-year period of global cooling and threatened the fragile foothold of North America's earliest human inhabitants.
     The discovery of 'shocked' nano-diamonds at Santa Rosa Island, located about 150 kilometres west of the Los Angeles shoreline, is being described as 'the strongest indicator yet' that prehistoric North America was rocked by a catastrophic cosmic explosion - with Hudson Bay the suspected epicentre of destruction. Several studies over the past few years have identified a telltale layer of charred material, hyper-radiated sediments and other traces of an extraterrestrial impact at a host of 12,900-year-old archeological sites across the U.S. and Canada, including three in Alberta and one in Manitoba. Controversy surrounds the theory that a comet blast was responsible for the Ice Age extinctions of so-called 'megafauna' species such as North American mammoths, camels and horses.
     Experts have traditionally attributed the disappearance of the creatures to climate change or over-hunting by spear-wielding 'Clovis' paleo-Indians who first settled the continent about 14,000 years ago. But the authors of the latest study argue that mounting evidence of a catastrophic impact event in Clovis-era Canada and the U.S. invites credible comparisons to the famous Chicxulub meteorite strike in Mexico - "the only previously known co-occurrence of nano-diamonds, soot and extinction," their paper states - that most scientists believe wiped out the dinosaurs 65 million years ago. The type of diamond we have found - Lonsdaleite - is a shock-synthesized mineral defined by its hexagonal crystalline structure. It forms under very high temperatures and pressures consistent with a cosmic impact," University of Oregon archeologist Douglas Kennett said. "These diamonds have only been found thus far in meteorites and impact craters on Earth and appear to be the strongest indicator yet of a significant cosmic impact."
     Earlier this year, Kennett published a study in the journal Science that identified traces of a different kind of micro-diamond and other signs of a cosmic impact at six sites in North America. In 2005, U.S. government chemist Richard Firestone and Arizona geologist Allen West - a co-author of the new paper - first proposed the idea that an exploding star sent a cataclysmic shower of debris to Earth soon after humans first migrated to North America from Siberia across the Bering land bridge. The latest study acknowledges the 'long-standing debate' between scientists over what caused the sudden demise of so many large Ice Age mammals. But the Kennett-led researchers conclude that the 'shock-synthesized' diamonds on Santa Rosa Island, along with 'soot and other wildfire indicators' there and at other Clovis sites, support the theory 'that the Earth crossed paths with a swarm of comets' 13 millennia ago, resulting in 'abrupt ecosystem disruption and megafaunal extinctions in North America.'

Sources: University of Oregon (20 July 2009), EurekAlert! (21 July 2009), Kelowna.com (22 July 2009)