New evidence that a comet explosion caused Earth's last mass extinction just 13,000 years ago

About 13,000 years ago, Earth faced sudden chaos. Ice was retreating, animals were thriving, and human groups carved out new lives. Then everything shifted for the Clovis people, possibly due to a comet explosion that resulted in Earth’s last mass extinction.

Mammoths and mastodons vanished. The Clovis people, known for their stone tools, disappeared from the record. At the same time, the climate flipped back into an icy phase called the Younger Dryas period.

Scientists have long argued about what triggered this change. Some point to overhunting. Others blame shifting climate patterns. A third idea reaches beyond Earth.

According to the Younger Dryas impact hypothesis, fragments of a comet exploded above the planet, unleashing fire, shockwaves, and a darkened sky.

Comet fragments at Clovis sites

To test this theory, a team led by Professor James Kennett of UC Santa Barbara searched for evidence of a comet impact at three classic Clovis-era sites: Murray Springs in Arizona, Blackwater Draw in New Mexico, and Arlington Canyon in California’s Channel Islands.

“These three sites were classic sites in the discovery and the documentation of the megafaunal extinctions in North America and the disappearance of the Clovis culture,” Kennett said.

Within the sediment layers, the researchers found quartz grains scarred by extreme heat and pressure.

Some carried fractures filled with melted silica, a feature that doesn’t form from volcanoes or campfires. Similar patterns exist at nuclear test sites and known impact craters.

The findings match what happens when a comet explodes low in the atmosphere. “In other words, all hell broke loose,” Kennett put it bluntly.

The blast would have lit fires across continents, filled the air with soot, and blocked sunlight.

Temperatures would have dropped quickly, creating an “impact winter.”

Ice sheets melted rapidly, adding more instability. Survival for giant animals and the Clovis people became unlikely under those harsh conditions.

Destruction across two continents

Other evidence supports this picture. Across North America and Europe, a mysterious black mat layer appears in sediments. It is rich in carbon, suggesting widespread burning.

Scientists have also found microscopic spherules, nanodiamonds, and meltglass. Rare elements like platinum and iridium show up in unusual amounts.

Each of these markers points to processes that occur during cosmic impacts, not ordinary Earth events.

The Younger Dryas boundary layer is now documented on five continents, covering millions of square miles. That scale rules out local causes and strengthens the case for a planetary event.

Shocked quartz and the Clovis comet

The strongest new clue comes from shocked quartz. Quartz is everywhere on Earth, but only extraordinary forces create the telltale parallel cracks and molten-filled fractures that researchers observed.

The Clovis sites contained these grains in the same sediment layers as other impact markers. Unlike the asteroid strike that created the Chicxulub crater, this event left no obvious scar.

A fragmented comet bursting above ground would have caused destruction and extinction without leaving a single giant crater. The signature of this comet survives only at the microscopic level.

Simulating cosmic destruction

To see if such an explosion could create the observed damage, the team ran computer simulations. They modeled a comet fragment about 328 feet (100 meters) wide hurtling into the atmosphere at 67,000 miles an hour (30 kilometers per second).

The fragment began breaking up high above Earth. The cascade ended in a massive fireball exploding just a few hundred meters above the surface.

The simulated blast released nearly 58 megatons of energy, far beyond any human weapon. Ground-level temperatures reached more than 30,000 K (53,540°F), enough to melt sediments and fracture quartz. Shockwaves traveled outward, creating the very patterns now seen in grains from the Clovis sites.

“There are going to be some very highly shocked grains and some that will be low-shocked. That’s what you would expect,” Kennett said.

Airbursts don’t deliver force evenly. Some quartz grains absorbed enormous pressures. Others felt less intense stresses. This variation matches what scientists actually found under the microscope.

Linking comet impact to extinction

Together, these discoveries make the comet airburst explanation harder to dismiss. Shocked quartz joins nanodiamonds, soot, meltglass, and rare elements in telling the same catastrophic story.

The Younger Dryas impact hypothesis links a sudden climate shift, the collapse of the Clovis culture, and the extinction of North America’s great animals to one catastrophic event in the sky.

The past continues to argue with itself as scientists weigh competing explanations for what happened at the onset of the Younger Dryas. Some point to hunting, others to shifting climates, and still others to something far more dramatic in the sky.

Yet with every fractured grain of quartz examined under the microscope, with every nanodiamond or layer of soot uncovered in the sediment, the case for a cosmic trigger grows stronger and more difficult to ignore.

The study is published in the journal PLOS One.

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