4/21/2016

Drilling Into Crater

A joint UK-US-led expedition has got under way to drill into the Chicxulub Crater off the coast of Mexico.

This is the deep scar made in the Earth's surface 66 million years ago by the asteroid that scientists believe hastened the end of the dinosaurs.


Today, the key parts of the crater are buried beneath 600m of ocean sediment. 

But if researchers can access its rocks, they should learn more about the scale of the impact, and the environmental catastrophe that ensued.

They are particularly interested in a feature called the "peak ring".

This was created at the center of the impact hole where the Earth rebounded after being hit by the city-sized object.
  • An 18km-wide impactor punched a hole in the Earth's crust some 100km across and 30km deep
  • This bowl then collapsed in on itself, leaving a crater about 200km across and a few km deep
  • The central zone of the crater rebounded and collapsed again, leaving an inner "peak ring"
  • Today, much of the Chicxulub Crater is buried offshore in the Gulf, under 600m of sediments
  • On land, the crater is covered by limestone deposits, but its rim is traced by an arc of sinkholes
In geophysical surveys that can sense beneath the ocean bed, the ring looks like an arcing chain of mountains.

"We want to know where the rocks that make up this peak ring come from," explained Prof Joanna Morgan, the co-lead investigator from Imperial College London.

"Are they from the lower, mid or upper crust? Knowing that will help us understand how large craters are formed, and that's important for us to be able to say what was the total impact energy, and what was the total volume of rock that was excavated and put into the Earth's stratosphere to cause the environmental damage," she told BBC News.

The cataclysm that occurred at the end of the Cretaceous Period doomed many species, not just the dinosaurs. All the material hurled upwards would have darkened the sky and cooled the planet for months on end.

But even as it took life away, the event also opened up new opportunities for those species that survived. 

And the expedition team wants to know if the impact zone itself became a life cradle. 

Because the asteroid hit what was back then a shallow sea area, it is likely the newly created crater was quickly filled with water. 

This water would have infused the hot and fractured rocks, leaching chemicals that could then sustain micro-organisms. 

Very similar conditions are seen today along the volcanic ridge that runs down the center of the Atlantic Ocean. 

"So it's possible we may encounter some exotic life in the fractured rocks we drill," said Prof Morgan. 

"This is very interesting for Chicxulub, but it's also fascinating to consider in terms of the early Earth or even Mars. 

On the early Earth, there would have been many more, larger impacts. 

We think life may well have originated in impact craters."
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