For the first time a team of Dartmouth researchers has linked an extraterrestrial impact in Canada to the dramatic change in Earth's climate and the dawn of the human civilization about 12,900 years ago.

The younger Dryas Stadial also known as the Big Freeze was a brief geological period of drought and cold conditions.  This near glacial condition was named after a flower that flourished in the cold conditions. Until today, a theory claimed that this event occurred due to the collapse of the North American ice sheets.

The theory suggests that a large quantity of water was held gathered behind an ice dam that eventually went into the Atlantic Ocean when the dam broke suddenly. This sudden entry of the water into the Atlantic Ocean was thought to shut down ocean currents that head tropical water northward producing cold and dry climate of the Younger Dryas.

But  Dartmouth University geochemist Mukul Sharma along with his colleagues opposes the previous theories that explain the rise in the meltwater from the North American ice sheet by providing conclusive evidence stating that the dramatic shift in climate occurred due to an object from space, either a comet or an asteroid.

The event took place some 12,900 years ago and triggered a colder and dryer climate across the world. The impact of the space object caused all big animals like camels, giant ground sloths and saber toothed cats to vanish in North America and also a group of human hunters referred to as Clovis people stopped hunting and turned into gatherers eating roots, smaller animals and berries.

"The Younger Dryas cooling is a very intriguing event that impacted human history in a profound manner," Sharma, a professor in the Department of Earth Sciences and one of the authors of a new paper said in a statement. "Environmental stresses may also have caused Natufians in the Near East to settle down for the first time and pursue agriculture."

In this study the researchers focused on spherules, droplets of solidified molten rock  released by the comet as it crashed into the Earth's atmosphere. The researcher obtained the spherules from boundary layers of Younger Dryas at various sites in Pennsylvania and New Jersey deposited at the beginning of the period. They then compared the geochemistry and mineralogy profiles of these spherules to the rocks  found in southern Quebec and discovered that both the samples matched.

"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," says Sharma, "even though we have not yet found its crater."

The study was published in the Proceedings of the National Academy of Sciences (PNAS).