Massive impact led to Big Freeze, researchers say
About 12,900 years ago, a massive asteroid or comet landed in Quebec, Canada. Shortly thereafter, the climate drastically changed around the globe, kicking off a period commonly called the Big Freeze. Now, scientists out of Dartmouth College say the two events are linked.
Scientists long believed that the climate changed so drastically because the North American ice sheet melted. It was previously thought that a massive dam in the North American ice sheet ruptured, causing loads of fresh meltwater into the Atlantic Ocean. The blast of freshwater was thought to have interrupted ocean currents, thereby impacting the weather patters and cutting off the northern flow of tropical waters. But the Dartmouth-led team says the impact of the comet or asteroid spurred the global climate shift.
In a study published this week in the journal Proceedings of the National Academy of Sciences (PNAS), the researchers challenge the idea that the Younger Dryas, or Big Freeze, had anything to do with rising meltwater.
"It may well have taken multiple concurrent impacts to bring about the extensive environmental changes of the Younger Dryas," lead researcher Mukul Sharma said in a press release. "However, to date no impact craters have been found and our research will help track one of them down."
The period featured abrupt cooling and long periods of drought. It takes its name from the Dryas octopetala flower, which blooms in cold conditions and thrived in Northern Europe through the Big Freeze. The frozen conditions led to the extinction, at least in North America, of animals such as camels, saber-toothed cats, giant ground sloths and mastodons. It led early humans to abandon hunting in exchange for a nomadic lifestyle and a diet featuring more berries, roots and smaller animals.
"The Younger Dryas cooling is a very intriguing event that impacted human history in a profound manner," Mukul Sharma, a professor in the Department of Earth Sciences and one of the authors, said in a press release. "Environmental stresses may also have caused Natufians in the Near East to settle down for the first time and pursue agriculture."
In reaching their conclusion, the scientists studied fragments of molten rock that were released by the comet or asteroid when it struck the Earth. They are continuing to look for the exact site of impact, where they expect to find a crater.
"What is exciting in our paper is that we have for the first time narrowed down the region where a Younger Dryas impact did take place," Sharma said, "even though we have not yet found its crater."
