Splosh! How the dinosaur killer asteroid created his crater

It's hard to imagine billions of tons of rock suddenly splashing like a liquid – but that's what happened when an asteroid hit the Earth 66 million years ago.

The scientists have now gathered a detailed picture of the minutes that followed the giant impact.

Remember that it is the colossal event that wiped out the dinosaurs.

The analysis of the drilled rocks in 2016 from the remains of crater shows that they have undergone a fluidization process.

The sprayed material literally began to behave as if it was a substance like water.

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• Dinosaurs suffered a catastrophic "winter"
• The asteroid strike makes the "instant Himalayas"

The models had predicted what should happen when a stony object of space, with a width of 12 km, struck the ground.

Initially, an almost instantaneous bowl would have been created about 30 km deep and up to 100 km wide.

Then, the instabilities would have seen the sides collapse inward and the base of the hole bounce to the sky, reaching briefly higher than the Himalayas.

Once everything was installed, there would remain a crater about 200 km wide and 1 km deep.

This is now buried beneath the sediments in the Gulf of Mexico, near the port of Chicxulub.

The description of the impact – scientists call it the model of dynamic collapse of crater formation – is only possible if the hammered rocks can, for a short time, lose some their resistance and flow without friction.

And this is the proof of this fluidization process that researchers are now reporting, after studying the rocks they drilled from what is known as the "peak circle" – that is to say a circle of hills in the center of the remaining depression of Chicxulub.

"What we found in the corer, is that the rock is fragmented." It was reduced to tiny fragments of initial size to the millimeter, which is the origin of this. fluid behavior that produces in the end the flat floor of the crater, which characterizes Chicxulub … and all these great impact structures, including those that we also see on the Moon, "explains Professor Ulrich Riller, from the University of Hamburg , in Germany.

It is not rock melting; It's rather rock that is broken by immense vibratory forces, says Professor Sean Gulick, co-director of the Drilling Team at the University of Texas in Austin, United States .

"It's a pressure effect; they are mechanical damage. The amount of energy moving through these rocks is equivalent to magnitude 10 or 11 earthquakes; the estimate for the whole impact is about 10 billion bombs for Hiroshima. "

In the end, the rocks will regain their strength. They must do it if they want to build the ring of hills.

This return of rigidity is again observed in drill core samples.

Chicxulub Crater – The impact that changed life on Earth

• A 12 km wide object dug a hole in the earth's crust 100 km deep and 30 km deep
• This bowl then collapsed, leaving a crater 200 km wide and a few km deep.
• The center of the crater bounced and collapsed again, producing an inner ring
• Today, a large part of the crater is buried offshore, under 600 m of sediment.
• On land, it is covered with limestone, but its edge is traced by an arch of sinkholes

"This is manifested by what we call shear fractures – plane discontinuities where rocks can slide over each other," added Professor Ulrich. "We see these fractures overprint the broken rocks that were formed earlier.These planar structures are proof that the rock must have found its resistance towards the end of the formation of the crater."

In addition to bringing new information on one of the most catastrophic days in the history of Earth and on the mass extinction that followed, the investigation on Chicxulub will also help scientists to study large craters impact on other planetary bodies.

"We explain a fundamental process that will occur on any rock body," says Professor Gulick.

"For the very first time, we now have rocks telling us the type of deformation they have undergone to behave temporarily like a liquid, and then back to being a rock at the end – without melting. This will be a fundamental process that will resurrect the planets, not only in our solar system, but probably in all solar systems. "

Professors Riller and Gulick participated in the Expedition 364 drilling project, which took place in April / May 2016 under the auspices of the European Consortium for Ocean Research Drilling (ECORD) and the International Ocean Discovery Program (IODP).

Their latest findings on "acoustic fluidization" in the Chicxulub Crater are published in the journal Nature.

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