The dinosaur-killing asteroid that struck Earth around 66 million years ago was huge — around 7 miles (12 kilometers) wide. So where are its remains? (Image credit: Sven Bachström via Alamy)
Around 66 million years ago, the reign of the dinosaurs came to a fiery end. An asteroid about 7 miles (12 kilometers) wide, flying at 27,000 mph (43,000 km/h), slammed directly into Earth. The impact triggered a cascade of deadly events that led to the fifth mass extinction that eliminated dinosaurs, with the exception of some birds.
But what happened to the Mount Everest-size asteroid?
When it smashed into Earth “with the energy of about 8 billion times a World War II-era nuclear bomb, the asteroid basically vaporizes,” Sean Gulick, research professor and co-director of the Center for Planetary Systems Habitability at the University of Texas at Austin, told Live Science. The asteroid became “a fine dust that ends up in the upper atmosphere and rains down” over the entire planet.
Decades of asteroid dust rained down to form what is now known as the iridium anomaly, a thin layer of rock that has 80 times more iridium than anywhere else in Earth’s crust, Gulick said. While iridium is highly concentrated in asteroids, it’s almost nonexistent in Earth’s outer shell — a key piece of evidence linking the 66 million-year-old layer to the dinosaur-killing asteroid.
Perhaps the only chunk of the asteroid known to exist is a sesame-seed-size fragment found by Frank Kyte, a geochemist at UCLA. The rock bit was discovered in a core sample drilled off Hawaii, Kyte reported in the journal Nature in 1998. More tiny shards were allegedly discovered in 2022, but that claim was not backed by peer review.
“We would have to get pretty lucky to find a larger chunk,” Gulick said. But if we did, scientists could learn more about the “process of shock” experienced by the asteroid itself and make even more precise estimates about the pressures and temperatures it experienced, for example.
The asteroid left behind a number of additional clues about its journey, including the huge crater it created when the giant rock collided with Earth. Roughly 110 miles (180 km) wide and about 12 miles (20 km) deep, the Chicxulub crater in what is now Mexico bears the massive scar of the asteroid. Named after a town near the center of the impact, the crater has been covered by rock and sediment that shifted over tens of millions of years and a major portion is hidden under the Gulf of Mexico. But still visible from the surface is an arc of sinkholes along part of its rim that formed in weakened limestone.
Related: What if a giant asteroid had not wiped out the dinosaurs?
The impact also generated a nearly mile-high tsunami that moved through the entire ocean, moving water as fast as 89 mph (143 km/h). The massive waves caused marks on the seafloor — called “megaripples” — that were as tall as five-story buildings and are preserved deep beneath Louisiana. A seismic survey revealed that the water that formed the ripples came from the direction of the Chicxulub crater.
Besides killing the unlucky creatures in the immediate area of the asteroid’s landfall and subsequent tsunami, the impact triggered a series of other devastating effects, including deadly acid rain and a global firestorm. But perhaps most destructive was the massive cloud of debris that shrouded Earth, drastically cooling the planet, blocking sunlight and photosynthesis, and collapsing the food chain (although the length of this “nuclear winter” is debated). The asteroid and its aftermath are widely agreed to be the cause of the nonavian dinosaurs’ extinction and ultimately wiped out about 75% of species on Earth.
“The energy release was like fighting total nuclear war, over and over again, 10,000 times,” said Alan Hildebrand, a planetary scientist and associate professor at the University of Calgary. Hildebrand co-authored the paper that published the discovery of the Chicxulub crater in 1991, and that work provided major evidence linking the crater’s connection to the death of the dinosaurs.
It’s no surprise to Hildebrand that the asteroid wiped out the majority of life on Earth.
In Alberta, where he was during the time of the interview, Hildebrand marveled at the sheer power of the impact. The nearby layer from the Chicxilub impact is 0.4 to 0.8 inches (1 to 2 cm) thick, “and that material was blasted up here from the Yucatán Peninsula,” he said.
