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These people argue that their findings show that mammoths weren't necessarily wiped out by cometary impact:
Researchers have previously suggested that the last mass extinction of animals on Earth was triggered by a comet colliding with the planet and sparking a sudden drop in temperature around 13,000 years ago.
This sudden change in climate, known as the Younger-Dryas climate reversal, saw many species of large mammals die out and also brought humans to the brink of extinction.
But scientists now claim to have disproved the controversial theory after finding a key piece of evidence used to support the comet impact idea could have been created by a more mundane process.
Another theory, which proposes that fresh water from a giant glacial lake glaciers poured into the North Atlantic, upsetting the ocean's currents which had helped keep most of the planet ice free, is now the most likely explaination for the shift in climate, which triggered the extinctions.
Scientists first put forward the idea that a comet was behind the extinctions after tiny crystals of carbon, known as nanodiamonds, were found in 12,900 year old sediment layers.
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They claimed these nanodiamonds were formed by the massive forces and temperatures created by an impact strike.
Experts said the presence of these nanodiamonds were evidence of a devastating impact by a comet or meteor, which threw millions of tonnes of dust into the atmosphere, causing the planet to cool.
However, researchers at Washington University in St Louis, Missouri, and Royal Hollway University of London, have found that these carbon crystals are not diamonds at all and are in fact clumps of another form of carbon known as graphene which commonly forms in sediments.
Professor Andrew Scott, one of the authors of the research at Royal Holloway University's earth sciences department, said: "Our results cast doubt upon one of the last widely discussed pieces of evidence supporting the Younger-Dryas impact hypothesis."
The Younger-Dryas climate reversal came at the end of a period known as the Pleistocene around 12,900 years ago.
During this period some of the largest mammals to have ever lived on land were spread throughout the globe, including mammoths, giant bears, mastodons – a large elephant-type creature – and sabre-toothed tigers.
Humans were also spreading into North America, but following the sudden shift in climate which triggered the onset of the last ice age, many of these species became extinct and humans are thought to have reduced to just a few thousand individuals.
Hunting by humans is often thought to have hurried the extinction of some of the giant mammals including mammoths, but scientists increasingly believe the main culprit was the sudden shift in climate.
Three years ago scientists at the University of Oregon found evidence of exotic materials, including nanodiamonds, in the 12,900 year old sediments that they claimed had come from a comet impact with the Earth.
Professor Scott and Tyrone Daulton, a materials expert at Washington University, believe that these diamonds were misidentified and they could find no evidence for a comet collision.
Dr Douglas Kennett, who led the University of Oregon team that first identified the nanodiamonds and suggested the comet theory, told Science magazine that Professor Scott and his colleagues had been looking in the wrong place.
"The claim that we have misidentified diamonds is false and misleading," he said.
Researchers have previously suggested that the last mass extinction of animals on Earth was triggered by a comet colliding with the planet and sparking a sudden drop in temperature around 13,000 years ago.
This sudden change in climate, known as the Younger-Dryas climate reversal, saw many species of large mammals die out and also brought humans to the brink of extinction.
But scientists now claim to have disproved the controversial theory after finding a key piece of evidence used to support the comet impact idea could have been created by a more mundane process.
Another theory, which proposes that fresh water from a giant glacial lake glaciers poured into the North Atlantic, upsetting the ocean's currents which had helped keep most of the planet ice free, is now the most likely explaination for the shift in climate, which triggered the extinctions.
Scientists first put forward the idea that a comet was behind the extinctions after tiny crystals of carbon, known as nanodiamonds, were found in 12,900 year old sediment layers.
Related Articles
How forests wiped out mammoths 16 Dec 2007
Woolly mammoths ate their own dung 08 Jul 2008
Woolly mammoth killed off by climate change 18 Aug 2010
'Super sized lions' roamed UK in ice age 30 Mar 2009
Mammoth task of reversing history 24 Oct 2006
Paw prints and poo could save the tiger05 Sep 2010
They claimed these nanodiamonds were formed by the massive forces and temperatures created by an impact strike.
Experts said the presence of these nanodiamonds were evidence of a devastating impact by a comet or meteor, which threw millions of tonnes of dust into the atmosphere, causing the planet to cool.
However, researchers at Washington University in St Louis, Missouri, and Royal Hollway University of London, have found that these carbon crystals are not diamonds at all and are in fact clumps of another form of carbon known as graphene which commonly forms in sediments.
Professor Andrew Scott, one of the authors of the research at Royal Holloway University's earth sciences department, said: "Our results cast doubt upon one of the last widely discussed pieces of evidence supporting the Younger-Dryas impact hypothesis."
The Younger-Dryas climate reversal came at the end of a period known as the Pleistocene around 12,900 years ago.
During this period some of the largest mammals to have ever lived on land were spread throughout the globe, including mammoths, giant bears, mastodons – a large elephant-type creature – and sabre-toothed tigers.
Humans were also spreading into North America, but following the sudden shift in climate which triggered the onset of the last ice age, many of these species became extinct and humans are thought to have reduced to just a few thousand individuals.
Hunting by humans is often thought to have hurried the extinction of some of the giant mammals including mammoths, but scientists increasingly believe the main culprit was the sudden shift in climate.
Three years ago scientists at the University of Oregon found evidence of exotic materials, including nanodiamonds, in the 12,900 year old sediments that they claimed had come from a comet impact with the Earth.
Professor Scott and Tyrone Daulton, a materials expert at Washington University, believe that these diamonds were misidentified and they could find no evidence for a comet collision.
Dr Douglas Kennett, who led the University of Oregon team that first identified the nanodiamonds and suggested the comet theory, told Science magazine that Professor Scott and his colleagues had been looking in the wrong place.
"The claim that we have misidentified diamonds is false and misleading," he said.
