Prehistoric climate change due to cosmic crash in Canada: Team ...

Prehistoric climate change due to cosmic crash in Canada: Team reveals cause of global climate shift 12,900 years ago
An artist's rendition of mastodons, camels and a ground sloth before the environmental changes of the Younger Dryas led to their extinction. Credit: Barry Roal Carlsen, University of Wisconsin
For the first time, a dramatic global climate shift has been linked to the impact in Quebec of an asteroid or comet, Dartmouth researchers and their colleagues report in a new study. The cataclysmic event wiped out many of the planet's large mammals and may have prompted humans to start gathering and growing some of their food rather than solely hunting big game.
The findings appear next week in the online Early Edition of the Proceedings of the National Academy of Sciences.
The impact occurred about 12,900 years ago, at the beginning of the Younger Dryas period, and marks an abrupt global change to a colder, dryer climate with far-reaching effects on both animals and humans. In North America, the big animals all vanished, including mastodons, camels, giant ground sloths and saber-toothed cats. Their human hunters, known to archaeologists as the Clovis people, set aside their heavy-duty spears and turned to a hunter-gatherer subsistence diet of roots, berries and smaller game.
"The Younger Dryas cooling impacted human history in a profound manner," says Dartmouth Professor Mukul Sharma, a co-author of the study. "Environmental stresses may also have caused Natufians in the Near East to settle down for the first time and pursue agriculture."
The high temperatures of the meteorite impact 12,900 years ago produced mm-sized spherules of melted glass with the mullite and corundum crystal structure shown here. Credit: Mukul Sharma
It is not disputed that these powerful environmental changes occurred, but there has long been controversy over their cause. The classic view of the Younger Dryas cooling interlude has been that an ice dam in the North American ice sheet ruptured, releasing a massive quantity of freshwater into the Atlantic Ocean. The sudden influx is thought to have shut down the ocean currents that move tropical water northward, resulting in the cold, dry climate of the Younger Dryas.
But Sharma and his co-authors have discovered conclusive evidence linking an extraterrestrial impact with this environmental transformation. The report focuses on spherules, or droplets of solidified molten rock expelled by the impact of a comet or meteor. The spherules in question were recovered from Younger Dryas boundary layers at sites in Pennsylvania and New Jersey, the layers having been deposited at the beginning of the period. The geochemistry and mineralogy profiles of the spherules are identical to rock found in southern Quebec, where Sharma and his colleagues argue the impact took place.
"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." There is a known impact crater in Quebec—the 4-kilometer wide Corossal crater—but based on the team's mineralogical and geochemical studies, it is not the impact source for the material found in Pennsylvania and New Jersey.
Using a binocular microscope, Dartmouth geochemist Mukul Sharma examines impact-derived spherules that he and his colleagues regard as evidence of a climate-altering meteor or comet impact 12,900 years ago. Credit: Eli Burakian
People have written about many impacts in different parts of the world based on the presence of spherules. "It may well have taken multiple concurrent impacts to bring about the extensive environmental changes of the Younger Dryas," says Sharma. "However, to date no impact craters have been found and our research will help track one of them down."
Citation:
Prehistoric climate change due to cosmic crash in Canada: Team reveals cause of global climate shift 12,900 years ago (2013, September 2)
retrieved 15 August 2023
from https://phys.org/news/2013-09-prehistoric-climate-due-cosmic-canada.html
This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no
part may be reproduced without the written permission. The content is provided for information purposes only.
Let us know if there is a problem with our content
Use this form if you have come across a typo, inaccuracy or would like to send an edit request for the content on this page.
For general inquiries, please use our contact form.
For general feedback, use the public comments section below (please adhere to guidelines).
Please select the most appropriate category to facilitate processing of your request
Your message to the editors
Your email (only if you want to be contacted back)
Thank you for taking time to provide your feedback to the editors.
Your feedback is important to us. However, we do not guarantee individual replies due to the high volume of messages.
E-mail the story
Prehistoric climate change due to cosmic crash in Canada: Team reveals cause of global climate shift 12,900 years ago
Note
Your email address is used only to let the recipient know who sent the email. Neither your address nor the recipient's address will be used for any other purpose.
The information you enter will appear in your e-mail message and is not retained by Phys.org in any form.
Your message
Newsletter sign up
Get weekly and/or daily updates delivered to your inbox.
You can unsubscribe at any time and we'll never share your details to third parties.
Your Privacy
This site uses cookies to assist with navigation, analyse your use of our services, collect data for ads personalisation and provide content from third parties.
By using our site, you acknowledge that you have read and understand our Privacy Policy
and Terms of Use.