The Younger Dryas Impact Hypothesis, controversial from the time it was presented in 2007, proposes that an asteroid or comet hit the Earth about 12,800 years ago causing a period of extreme cooling that contributed to extinctions of more than 35 species of megafauna including giant sloths, sabre-tooth cats, mastodons and mammoths.
It also coincides with a serious decline in early human populations such as the Clovis culture and is believed to have caused massive wildfires that could have blocked sunlight, causing an "impact winter" near the end of the Pleistocene Epoch.
In a new study published in the journal Scientific Reports, University of South Carolina archaeologist Christopher Moore and 16 colleagues present further evidence of a cosmic impact based on research done at White Pond near Elgin, South Carolina.
The study builds on similar findings of platinum spikes an element associated with cosmic objects like asteroids or comets in North America, Europe, western Asia and recently in Chile and South Africa.
"There have been numerous papers that have come out in the past couple of years with similar data from other sites that almost universally support the notion that there was an extraterrestrial impact or comet airburst that caused the Younger Dryas climate event," said Moore.
"First, we thought it was a North American event, and then there was evidence in Europe and elsewhere that it was a Northern Hemisphere event. And now with the research in Chile and South Africa, it looks like it was probably a global event," he added.
In addition, a team of researchers found unusually high concentrations of platinum and iridium in outwash sediments from a recently discovered crater in Greenland that could have been the impact point.
Although the crater hasn't been precisely dated yet, Moore said the possibility is good that it could be the "smoking gun" that scientists have been looking for to confirm a cosmic event.
Additionally, data from South America and elsewhere suggests the event may have actually included multiple impacts and airbursts over the entire globe.
While the brief return to ice-age conditions during the Younger Dryas period has been well-documented, the reasons for it and the decline of human populations and animals have remained unclear. The impact hypothesis was proposed as a possible trigger for these abrupt climate changes that lasted about 1,400 years.
The conventional view has been that the failure of glacial ice dams allowed a massive release of freshwater into the north Atlantic, affecting oceanic circulation and causing the Earth to plunge into a cold climate.
The Younger Dryas hypothesis simply claims that the cosmic impact was the trigger for the meltwater pulse into the oceans.
"We speculate that the impact contributed to the extinction, but it wasn't the only cause. Over hunting by humans almost certainly contributed, too, as did climate change," Moore noted.
( With inputs from IANS )