Chicxulub Crater: The Beginning of the End for the Dinosaurs

Around 66 million years ago, the last of the dinosaurs (aside from birds) were wiped out.

The pterosaurs, flying reptiles closely related to dinosaurs, also went extinct. Alongside them, the giant marine reptiles of the era, such as plesiosaurs and the mosasaurs made famous in 'Jurassic World,' also perished.

This was part of a global mass extinction event. During this dark period in Earth's history, about 75 percent of all species alive at the time were wiped out.

So, what exactly happened? This question has sparked debates for decades. However, in 1978, an important clue was uncovered along the Mexican Gulf Coast.

At the time, geologists from the Pemex petroleum company were conducting a magnetic survey in the Caribbean. Using their instruments, they detected something hidden from the naked eye: a mysterious arc buried beneath the seabed, just to the north of Mexico's Yucatán Peninsula.

Further investigation revealed that this arc was actually part of a colossal underground crater.

The crater, which stretches across the northern coastline of the Yucatán Peninsula and some of the surrounding ocean floor, is enormous, with an estimated diameter ranging from 112 to 124 miles (180 to 200 kilometers).

Even after all these years, we are still coming to terms with the consequences of that groundbreaking discovery.

The 1978 survey provided scientists with their first glimpse of the signature left by a massive extraterrestrial object. It could have been caused by an asteroid impact or possibly even a comet. Whatever the cause, we now know that the object collided with Earth around 66 million years ago — precisely at the time when non-avian dinosaurs vanished from the fossil record.

It's Known as the Chicxulub Impact Crater

The hidden landmark was dubbed the Chicxulub crater, named after the nearby village of Chicxulub in Mexico, which lies near its center. The space object that collided with Earth millions of years ago is referred to as the Chicxulub impactor.

The majority of experts believe the impactor was an asteroid. However, some research — such as a 2021 study published in the journal Scientific Reports — has challenged this, suggesting that the object was more likely a comet.

Asteroids are composed of rocky materials, while comets contain rock as well, but they also carry ice and dust, distinguishing them from asteroids.

A critical piece of evidence in the ongoing "asteroid vs. comet" debate regarding the Chicxulub crater is the element iridium. This rare substance is seldom found in Earth's crust but is much more abundant in asteroids.

When the object that formed the Chicxulub crater struck the Gulf of Mexico, it didn't just create a crater. It also dispersed iridium across the Earth's surface.

Let's set the stage. Dinosaurs emerged during the Mesozoic Era, which spanned from 252 to 66 million years ago. This was followed by the Cenozoic Era, often referred to as the "Age of Mammals." We continue to live in the Cenozoic today.

The final part of the Mesozoic is known as the Cretaceous Period. In contrast, the first segment of the Cenozoic is called the Paleogene Period. (Are you still following along?)

Across the globe, rocks from the geologic layers marking the end of the Cretaceous Period, 66 million years ago, contain unusually high concentrations of iridium. These phenomena serve as a reminder of one of the most catastrophic events in Earth's history.

The Chicxulub Impact Was Devastating

It would be an understatement to say that the planet transformed at the end of the Mesozoic era. The Cretaceous-Paleogene Extinction Event (K-Pg Event) wiped out numerous species, creating opportunities for mammals to eventually occupy ecological roles once filled by dinosaurs and marine reptiles.

While there is still much uncertainty about the precise impact of the Chicxulub event on the crisis, volcanic activity and the emissions from it might have also played a significant role in the extinction. However, a study conducted in 2020 casts doubt on this theory.

The scientific consensus suggests the object that formed the Chicxulub crater was around 8.7 miles (14 kilometers) wide when it struck the Gulf of Mexico. According to a 2022 study, this massive impact likely triggered an enormous tsunami.

Using advanced computer models and data gathered from over 100 geological sites worldwide, a team led by researchers from the University of Michigan successfully simulated the ocean's response to the catastrophic impact.

Brian Arbic, a researcher from Michigan, shared an enlightening description with us in a recent email. He explained, "Within the first 5 to 40 seconds after impact, our model suggests a rising rim wave approximately 25 kilometers (15 miles) tall," Arbic notes.

By the 600-second mark, the great wave would have lost some of its height due to time and distance. However, the vast ocean was still in for a turbulent day.

"Waves reaching about 5 meters [16.4 feet] were present in the open North Atlantic and South Pacific oceans, far from the point of impact," Arbic mentioned. He further added that the event "would have overshadowed any recent tsunamis," potentially flooding coastlines worldwide.

The Chicxulub Impact Also Triggered Acid Rain and Wildfires

Things in the sky weren’t looking much better after the impact event either.

Upon impact, the space object caused both rock and seawater to vaporize. The resulting geological debris was thrown into the atmosphere, later falling back to Earth and generating enough friction to trigger a "heat pulse" throughout the atmosphere.

"Numerous studies have outlined the swift temperature changes following the impact, as well as the ensuing acid rain," says Ted Moore in an email. Moore is a co-author of the 2022 study and one of Arbic's colleagues at the University of Michigan.

"Both of these effects would have been detrimental to life on Earth. However, I believe the most significant factor affecting plant life was the 'nuclear winter' — the dramatic reduction in sunlight," Moore adds.

A surge of ancient wildfires swept across the planet, filling the atmosphere with ash and smoke, plunging the Earth into darkness for prolonged periods.

"In the absence of natural sunlight, many plants would have struggled to survive, and plants form the foundation of the food web. All creatures above this base rely on them for sustenance," he clarifies. Microscopic phytoplankton — plant-like organisms essential to marine ecosystems — faced a similar predicament.

The Aftermath

"In the short run, planktonic organisms typically undergo rapid turnover — within days, weeks, or a few months, reproduction occurs. Without the swift reproduction of the single-celled algae that constitute much of marine phytoplankton, the herbivores would perish. And when those plant feeders die, the animals that feed on them die as well, continuing up the food chain," explains Moore.

Simply put, large animals couldn't gather enough energy to survive. Tyrannosaurus rex, Triceratops, and their relatives were doomed.

However, not everything was lost. Plants had a secret weapon.

"On land, plants generate seeds or spores that can remain dormant in the soil for at least one season before sprouting. In the ocean, some marine phytoplankton produce 'resting spores' when conditions are unfavorable. These spores sink and 'rest' until conditions improve," Moore says. "As a result, certain plant species could make a comeback. It's much harder for animals to do the same."

Challenging, yes. But not beyond possibility.

Many creatures that were smaller and less specialized than the extinct dinosaurs managed to survive the cataclysm. Mammals exploded in diversity. Ground-dwelling birds adapted to environments where forests had been destroyed by wildfires.

It's not an overstatement to say that without the K-Pg extinction event, humanity might never have emerged.

As the planet recovered, corals and sediments gradually buried the Chicxulub crater. Although it may not be visible to the naked eye, your very existence stands as proof of the long-lasting effects of that cataclysmic event. Life persevered from the wreckage.