Sixty-eight million years ago, an asteroid the size of a small city hit the earth. This impact, which was to lead to the end of the dinosaurs, left a scar several miles underground and more than 115 miles wide.
Chicxulub, located beneath the Mexican peninsula of Yucatán, is the best preserved large impact crater on earth, though it is buried under half a mile of rock. It is also the only crater on the planet with a mountainous ring of shattered rocks within its outer edge, called a top ring. How these traits develop has long been debated, but a new study in Nature shows that they are a product of extremely strong vibrations in the earth that cause stone to flow like liquid for a few minutes after impact. 1
"For a while, the broken rock behaves like a liquid," said Jay Melosh, a professor of Earth, Atmospheric and Planetary Sciences at Purdue University. "There are a lot of theories about what mechanism this fluidization allows, and now we know that it's really strong vibrations that constantly shake the stone to make it flow."
This mechanism, known as "acoustic fluidization," is the process that allows the ring of mountains in the center of the crater to rise within a few minutes of the impact of the asteroid. (This idea was first proposed by Melosh in 1979). Craters are essentially the same on all terrestrial planets (Earth, Mercury, Venus, Mars and Moon), but for obvious reasons they are hard to study in space: we can not look at them with the same details we can rely on Earth
The Chicxulub Crater is not easily accessible even by traditional standards; It was buried in the last 66 million years. Thus, the International Ocean Discovery Program (a group within the International Continental Scientific Drilling Program) has done the only thing they could – they dug. The team drilled a six-inch diameter core and a mile into the earth, collecting rocks that were shattered and partially melted by the impact that wiped out the dinosaurs.
In the study of fracture zones and patterns in the core of international research The team found an evolution in the vibrational sequence that would allow the flow of debris.
"These results help us to understand how impact craters collapse and how large rock masses behave fluid under other circumstances such as landslides and earthquakes," Melosh said. "Cities were wiped out by massive landslides where people thought them safe, but then they discovered that rocks flowed like liquid when a disturbance sets a sufficiently large mass in motion."
The extinction of the dinosaurs themselves was probably not directly influenced by the internal collapse of the crater – other, external effects of the impact they did, said Melosh. Regardless, it is important to understand the consequences of a major asteroid impact on Earth. Since crater formation is the same on all terrestrial planets, these results also confirm the mechanisms of effects throughout the solar system.
Header Image – A kilometer-long sediment core drilled by the International Ocean Discovery Program helped researchers discover how the Chicxulub crater was formed. Credit: International Ocean Discovery Program