A Comet Exploded Above North America 12,800 Years Ago, Say Scientists

Scientists have found evidence for the so-called Younger Dryas Impact hypothesis that a comet exploded in Earth’s atmosphere 12,800 years ago, causing temperatures on Earth to dip.

A paper published in the journal Airbursts and Cratering reveals hints of an ancient cosmic airburst in three separate sites in New Jersey, Maryland and South Carolina. The evidence includes platinum, meltglass and shock-fractured quartz, all suggesting the kinds of forces and high temperatures associated with “airburst” comets.

This is similar to what happens during atomic detonations near Earth’s surface.

‘Touchdown’ Airbursts

Though massive asteroids and comets strike Earth, causing craters, most explode in the air as fireballs or airbursts. “What we’ve found is that the pressures and temperatures were not characteristic of major crater-forming impacts but were consistent with so-called “touchdown” airbursts that don’t form much in the way of craters,” said James Kennett, emeritus professor at the University of California, Santa Barbara.

It’s thought that the burning caused by the comet airburst may also have killed off megafauna in North America, such as mammoths and giant ground sloths.

Thousands Of Pieces

During the event, a comet around 62 miles (100 kilometers) wide probably fragmented into thousands of pieces. That would explain the sediment layer across much of the northern hemisphere that contains materials associated with impacts, such as iridium, platinum, melt-glass and nano-diamonds.

Similarly fractured quartz grains and melt-glass have been found at the Trinity atomic bomb test site in New Mexico, where a 20-kiloton bomb was detonated in July 1945 atop a 100-foot (30.5-meter) tall tower.

Tunguska Event

One of the most famous cosmic airbursts was the so-called “Tunguska Event” of 1908, when a shockwave from a 130-foot (40-meter) asteroid or comet fragment exploded about six miles (120 kilometers) above Siberia. It destroyed 830 square miles (2,150 square kilometers) of forest.

This isn’t the only comet strike thought to have significantly affected Earth’s climate and biodiversity. It’s known that an asteroid or comet hit Earth close to Mexico’s Yucatán Peninsula 66 million years ago, causing the 110-mile (180 kilometers) wide Chicxulub crater. The strike is thought to have caused an impact winter lasting decades that killed the dinosaurs.

Cosmic Companion

In 2022, scientists announced that they had found a suspected second asteroid impact crater of a similar age below the North Atlantic Ocean off the coast of Guinea, West Africa, that measures five miles (nine kilometers) wide. It suggests that the space rock that killed the dinosaurs may have had a smaller cosmic companion or have been part of a cluster.

Only 200 impact craters have been discovered on Earth’s surface so far—about a tenth of them on the seabed—despite asteroids striking for its entire existence.

Wishing you clear skies and wide eyes.

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