66 million years ago a 15km-wide asteroid hit the earth just off the coast of Mexico’s Yucatan Peninsula. The aftermath of this event is thought to have driven the extinction of many creatures, most famously – the dinosaurs. Earthquakes that would top the Richter scale, several-kilometer-high tsunamis and raging forest fires wreaked havoc upon the earth. Debris from the impact was thrown into the sky and blocked sunlight for months, perhaps years, causing the earth’s climate to cool drastically.
Chicxulub Crater – ground zero of the impact – is now mostly buried under ocean sediments. Earlier this year Professor Joanna Morgan, a geophysicist of Imperial College London, and her team drilled into the crater’s rim to study the composition and depth of specific rocks in an attempt to confirm the dynamic collapse model of crater formation.
When the ancient asteroid hit the side of the Yucatan peninsula it tore a 100km-wide, 30km-deep hole in the earth’s crust. The sides fell in on themselves, widening the crater, and the center rebounded as a mountain taller than Everest was briefly pushed up, before crumbling back down to create a ‘peak ring’ of basement rock. This entire process took no longer than 10 minutes. In this model the peak ring should contain the rocks that moved the farthest.
Drilling into the peak ring they found pink granite that had been raised from 10km down to just a few hundred meters below the surface – the crust had been effectively turned inside-out. Finding this basement rock from the depths of the earth’s crust so close to the surface was astounding and complemented the dynamic collapse model. Analysis of the rocks showed they were fractured as if they had experienced extreme pressure. Amazingly, the power of the impact caused the rocks to temporarily lose cohesion so that they ‘flowed’ – acted like a semi-molten liquid.
The data from this expedition will be important for modelling the composition of the interior of other planets and moons. By drilling into the peak rings of craters on other planets we will be able to determine the make-up of their crusts without the need to drill down for several kilometers – an exciting step for geophysics.