Chicxulub Crater: Where the End of the Dinosaurs Began

Scientists named this unseen landmark the Chicxulub crater, after Chicxulub, Mexico, a village close to its geographic center. The offending space object that hit our planet tens of millions of years ago is called the Chicxulub impactor.

Most experts think the impactor was an asteroid. However, some studies — including a 2021 paper published in the journal Scientific Reports — have disputed this, arguing that it's more likely the object was a comet.

For those keeping score at home, asteroids are made of rocky material. Comets contain rock as well, but unlike asteroids, they're also loaded with ice and dust.

One key bit of evidence in the "asteroid versus comet" discourse regarding the Chicxulub crater is the element iridium. You'll rarely find this stuff in Earth's crust, but it's a lot more common in asteroids.

When the object that created the Chicxulub impact crater landed in the Gulf of Mexico, it didn't just leave a crater behind. It also scattered iridium all over the planet's surface.

Allow us to set the scene. Dinosaurs first evolved in the Mesozoic Era, which lasted from 252 to 66 million years ago. This was followed by the Cenozoic Era, sometimes known as the "Age of Mammals." We're still living in the Cenozoic today.

The last part of the Mesozoic is called the Cretaceous Period. And the first chunk of the Cenozoic is the Paleogene Period. (Are you with us so far?)

All over the world, rocks from the geologic layers that mark the end of the Cretaceous Period 66 million years ago contain abnormally high levels of iridium. The phenomena are a testament to one of the most catastrophic episodes in Earth's history.

Saying our planet changed when the Mesozoic ended would be a gross understatement. By killing off so many different species, the Cretaceous-Paleogene Extinction Event (or the K-Pg Event for short) allowed mammals to eventually fill in some of the niches vacated by dinosaurs and marine reptiles.

There's a lot we still don't know about the Chicxulub incident's exact role in the crisis. Volcanic activity (and the emissions it released) could have been another major driving force behind the extinction — although a 2020 study questions that idea.

The scientific community estimates the object that created the Chicxulub crater was a whopping 8.7 miles (14 kilometers) in diameter when it hit the Gulf of Mexico. According to a 2022 study, that airstrike set off one heck of a tsunami.

With powerful computers and data collected from more 100 geologic sites across the globe, a team led by scientists at the University of Michigan was able to simulate how the ocean took the blow.

One of those researchers was Michigan's own Brian Arbic, who painted a vivid picture for us in a recent email. "In the first five to 40 seconds or so after impact, our model predicts an advancing rim wave of about 25 kilometers (15 miles) high," Arbic says.

Time and distance would've caused the great wave to lose some height by the 600-second mark. But the deep blue sea was still in for a rough day.

"There were waves of about 5 meters [16.4 feet] high in the open North Atlantic and South Pacific oceans, far from the impact site," said Arbic. He adds that the episode "would have dwarfed any recent tsunamis," flooding coastlines worldwide.

After the impact event, things in the sky weren't too rosy either.

On impact, the space object vaporized rock and seawater alike. Geologic debris kicked up by the collision later rained back down, producing friction that set off a "heat pulse" through the atmosphere.

"Many papers have described the rapid changes in temperature following the impact, as well as the resulting acid rain," says Ted Moore via email. He's a co-author of the 2022 study and one of Arbic's colleagues at the University of Michigan.

"Both of these effects would have had negative impacts on life on Earth. But I believe the key element that strongly affected plant life was the 'nuclear winter' — the great decrease in sunlight," Moore says.

An epidemic of prehistoric wildfires filled the skies with dust and soot, darkening the planet for years on end.

"Without normal sunlight many plants would have not been able to survive and plants are the base of the food chain. Every animal above that base depends on them for life," he explains. Microscopic phytoplankton — plant-like organisms critical to marine ecosystems — faced the same challenge.

"In the short-term, planktonic life tends to have a fairly rapid turnover — a few days to a few weeks or months pass before some form of reproduction takes place. Without the rapid reproduction of the single cell algae that form much of the marine phytoplankton, the plant feeders would die and when they die, the animals that eat the plant feeders die and so on up the food chain," Moore says.

Simply put, large animals couldn't find enough calories to keep themselves alive. Tyrannosaurus rex, Triceratops and their cousins were done for.

Yet all was not lost. Botanical life forms had an ace up their sleeves.

"On land, plants produce seeds or spores that can lie in the soil for at least one season before germinating. In the ocean, some of the marine phytoplankton produce 'resting spores,' especially when environmental conditions are not optimal. They sink down and 'rest' long enough for conditions to change," says Moore. "Thus, some of the plant species could come back. It is a lot more difficult for animals to do the same."

Difficult, sure. But not impossible.

Many creatures who were smaller and less specialized than the bygone dinosaurs weathered the storm. Mammals diversified like crazy. Ground-dwelling birds made do in places that had lost their forests to wildfires.

And it's no exaggeration to say that without the K-Pg extinction, human beings probably never would have evolved.

As the world healed, corals and sediment slowly buried the Chicxulub crater. You might not be able to see it with the naked eye, but your very existence is a testament to the blast's long-ranging effects. From the ashes of disaster, life forged ahead.