At the end of the Pleistocene era around 13,000 years ago, North America lost most of its megafauna—including mastodons, giant ground sloths, saber-toothed cats, and short-faced bears. Some researchers think the mass extinction was caused by climatic changes or maybe even humans; others think it was the abrupt environmental changes resulting from a comet collision with Earth that led to the Younger Dryas period of global cooling just a couple centuries later.
In a new study published in the Journal of Geology, researchers argue for the latter hypothesis. They suggest that the same cosmic impact that took out the Pleistocene megafauna may have also created tiny diamonds across at least three continents around 12,800 years ago.
Cosmic collisions such as these produce a type of material called nanodiamonds. To date, the only other layer where more than one nanodiamond has been found is the Cretaceous-Tertiary boundary (now known as the Cretaceous-Paleogene boundary) from 65 million years ago, famous for the extinction of dinosaurs.
Now, a large international team working at 32 sites in 11 countries have found an abundance of nanodiamonds distributed over 50 million square kilometers across the Northern Hemisphere at the Younger Dryas boundary (YBD)—a carbon-rich layer that appears as a thin black line just a few meters below the surface.
“We conclusively have identified a thin layer over three continents, particularly in North America and Western Europe, that contain a rich assemblage of nanodiamonds, the production of which can be explained only by cosmic impact,” says James Kennett from the University of California, Santa Barbara. The strewnfield of this major cosmic impact covers at least 10 percent of the planet.
The nanodiamonds in the YDB were found in several forms, including cubic (the kind used in jewelry) and hexagonal crystals. These different types are the result of large variations in temperature, pressure, and oxygen associated with the chaos of an impact. “These are exotic conditions that came together to produce the diamonds from terrestrial carbon,” Kennett says in a news release. “The diamonds did not arrive with the incoming meteorite or comet,” he adds. A cubic nanodiamond from Murray Springs, Arizona, is pictured to the right.
The team also found many other YDB material, some of which formed at temperatures in excess of 2,200 degrees Celsius and that “could not have resulted from wildfires, volcanism or meteoritic flux, but only from cosmic impact,” Kennett explains.
Images: UC Santa Barbara