Geologists have unearthed new evidence that a massive asteroid or comet smashed into the planet some 12,900 years ago during a period called the Younger Dryas, a time marked by unusual cold temperatures and the extinction of many large animals in North America, including mammoths, mastodons and saber-tooth cats.

ANALYSIS: Why the Younger Dryas Matters

The telltale clues are embedded in a thin layer of 13,000-year-old sediment buried beneath Lake Cuitzeo in central Mexico. The impact hypothesis for the cause of the Younger Dryas boundary layer, seen in several locations in North America, Greenland, and Western Europe has come under repeated scrutiny over the years. This is the first time evidence has extended into Mexico and the tropics.

The sediment contains an exotic assortment nanodiamonds, impact spherules and other materials, some of which could only have been formed through a cosmic impact, the new analysis shows.

Based on the findings, authors of the study say it is likely that an asteroid or comet bigger than several hundred meters in diameter skimmed through the atmosphere and crashed into the ground, burning vegetation, melting rocks and disrupting the environment on impact. The impact hypothesis tied to the Younger Dryas event is often referred to as the Clovis comet hypothesis, after the Clovis culture that existed in North American during this time at the end of the last glacial period.

"We have examined multiple hypotheses to account for these observations and find the evidence cannot be explained by any known terrestrial mechanism," the authors write. "It is, however, consistent with the Younger Dryas boundary impact hypothesis postulating a major extraterrestrial impact involving multiple airbursts and/or ground impacts at 12,900 years ago," they conclude.

NEWS: As Mammoths Died Out, Earth Chilled

“These results are consistent with earlier reported discoveries throughout North America of abrupt ecosystem change, megafaunal extinction, and human cultural change and population reduction,” James Kennett, professor of Earth science at the University of California at Santa Barbara, said in a statement.

The research appears in the Proceedings of the National Academy of Sciences.


Map of Lake Cuitzeo: Upper image is a digital elevation model of Lake Cuitzeo in the Mexican State of Michoacán. The lower map shows the lake’s location within Mexico with the drainage basin in white area and the coring site in yellow. (PNAS)

A cosmic impact is believed to be responsible for making one spherule collide into another. (University of California, Santa Barbara)

Images of single and twinned nanodiamonds. Each dot represents a single atom. (University of California, Santa Barbara)