Chicxulub: The asteroid that killed the dinosaurs

A crater at the edge of the Yucatán peninsula in Mexico was created by a massive asteroid that hit Earth 66 million years ago

The Chicxulub impactor

At the end of the Cretaceous Period 66 million years ago, an asteroid the size of a city collided with Earth. The Chicxulub impactor, as it is called, was somewhere between 10 and 15 kilometres in diameter.

The collision was devastating: rocks from deep within Earth’s crust were raised 25 kilometres high and a rim of mountains taller than the Himalayas formed around the crater’s edge.

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The asteroid hit at 20 kilometres per second from an angle of 60 degrees above horizontal – just right for sending the maximum amount of vaporised rock into the atmosphere. Plumes of sulphur-based gases and fine dust blocked out the sun, causing an “impact winter” that lasted for 15 years.

Sun-blocking dust from asteroid impact drove the dinosaur extinction

The Chicxulub impact 66 million years ago filled the sky with fine silicate dust, which blocked out sunlight and lingered for 15 years

At the time, Earth was populated by dinosaurs, who had been the dominant life form for nearly 200 million years. The Chicxulub impactor is widely thought to have changed all that, leading to the dinosaur’s eventual extinction (and the evolution of surviving dinosaurs into today’s birds).

The impact hypothesis was first proposed to explain this mass extinction (called the Cretaceous–Palaeogene extinction event) by Nobel prize-winning physicist Luis Alvarez and his son Walter Alvarez in the 1970s, but not everyone agrees that the story is so simple. Others think the dinosaurs were already on their way out, a journey accelerated – but not caused – by this visitor from outer space.

Chicxulub crater

The asteroid left a crater over 150 kilometres wide, centred just off the coast of the Yucatán peninsula in Mexico. It was named after Chicxulub Pueblo, a small town close to this point. The crater was first discovered by scientists working for the Mexican state-owned oil company Pemex in the 1960s, but it wasn’t until 1990 that researchers linked it to the Cretaceous–Palaeogene extinction event.

In 2022, a 9-kilometre-wide crater, made at about the same time as the Chicxulub crater, was found near the coast of West Africa. Researchers have speculated that it might have been made by a piece that broke off the Chicxulub asteroid.