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. link:http://www.telegraph.co.uk/earth/earthnews/7981798/Comet-impact-did-not-cause-mammoths-to-die-out-say-scientists.html added by: Kristena
