Around 13,000 years ago, something dramatic happened on Earth.
Mammoths, mastodons, and many other giant animals suddenly disappeared.
At the same time, the Clovis people—famous for their distinctive stone tools—vanished from the archaeological record across North America.
Scientists have long debated what caused this sudden shift, and now new evidence adds weight to the idea that the sky itself played a destructive role.
A team of researchers led by UC Santa Barbara’s James Kennett has discovered grains of “shocked quartz” at three famous archaeological sites: Murray Springs in Arizona, Blackwater Draw in New Mexico, and Arlington Canyon on California’s Channel Islands.
Shocked quartz forms when sand grains are subjected to extreme heat and pressure—conditions that are most often linked to cosmic impacts.
The findings, published in PLOS One, strengthen a growing body of evidence for what’s known as the Younger Dryas impact hypothesis.
This hypothesis suggests that a fragmented comet exploded in the skies over Earth at the onset of the Younger Dryas, a sudden cold snap that lasted about a thousand years in what should have been a warming climate after the Ice Age.
The explosions would have created shockwaves, massive fires, and plumes of soot and dust that darkened the skies and cooled the planet. “In other words, all hell broke loose,” Kennett says.
For years, Kennett and his colleagues have been piecing together this story. They’ve identified unusual “black mat” layers in sediments across North America and Europe that point to widespread fires.
They’ve also found rare elements like platinum and iridium, which are common in comets, and minerals formed only under intense heat, such as nanodiamonds and glassy spherules. The discovery of shocked quartz now adds what Kennett calls a “crème de la crème” piece of evidence.
What makes shocked quartz so important is that it provides direct proof of extreme pressures and temperatures far beyond anything caused by volcanic eruptions or human activity. In this case, the quartz grains not only showed cracks but also melted silica, confirming the violent forces at play.
Unlike the massive asteroid that wiped out the dinosaurs 65 million years ago and left a crater in Mexico’s Yucatán Peninsula, the proposed Younger Dryas event may not have left an obvious impact crater.
That’s because the comet likely exploded in the air—what scientists call an “airburst.” Such explosions don’t always leave scars on the landscape, but they can still devastate ecosystems.
To understand this better, the team used computer models to simulate low-altitude cosmic explosions.
These showed how different pressures and temperatures could produce the range of shock patterns observed in the quartz grains. Some grains were heavily shocked, while others were only lightly affected—exactly what would be expected from a fragmented comet bursting in the sky.
Combined with other impact markers found in the same layers—soot-rich sediments, nanodiamonds, and impact spherules—the discovery of shocked quartz strengthens the case for a catastrophic cosmic event.
The researchers argue this event may have been a key driver of the megafaunal extinctions and the collapse of the Clovis culture during the Younger Dryas.
In short, the new findings suggest that when the Clovis people and mammoths disappeared, it wasn’t just the changing climate at work.
The sky itself may have exploded, reshaping the course of life in the Americas.
