Earth-shattering, deadly asteroid strikes might also create safe harbour for life. An expedition to the Chicxulub crater has drawn a new timeline of how the cataclysmic impact that probably killed the dinosaurs happened – and how it may have carved out new niches in which life could flourish, even in the face of utter destruction.
About 65 million years ago, a giant asteroid plummeted through Earth’s atmosphere and punched through the planet’s crust in what is now Chicxulub, in Mexico’s Yucatan peninsula. That makes it one of the youngest and most accessible craters in the solar system – others are too distant or have had the story of their origins eroded by time and plate tectonics.
So Joanna Morgan, a geophysicist at Imperial College London, and her colleagues boarded an offshore platform in the Gulf of Mexico this April and May and drilled into the crater’s edge, which lies beneath the sea and about a kilometre of limestone.
Now, they have a detailed picture of exactly what happened to the rock as the crater formed – and the details are surprising.
“It’s absolutely crazy, but it tells us absolutely fundamentally how craters are formed,” Morgan says.
Max Alexander/B612 Foundation/Asteroid Day
The team retrieved samples from between 506 metres and 1335 metres beneath the seafloor, says Sean Gulick, a geophysicist at the University of Texas at Austin and an expedition leader. The samples from 506 metres down turned out to be sediments that were laid down long after the impact, between 56 and 34 million years ago.
But the deeper they dug, the more they found so-called basement rocks, representing granites from the depths of Earth’s crust. Finding old granite so close to the surface, just a kilometre below the seafloor, it was like the crust was upside down, Morgan says.
By analysing the depths and compositions of the rocks, the team reconstructed a timeline for the impact.
First the asteroid blasted through almost all of Earth’s crust, propelling rocks from the bottom of the crust and lifting them 25 kilometres within 10 minutes. At the rim of the newly forming crater, a mountain range higher than the Himalayas lifted and collapsed within three minutes, leaving a halo of basement rock in a geological feature called a peak ring. At the centre, a massive peak of rock splashed upward, fluid-like, before collapsing again – much like the splash of a sugar cube in a cup of hot tea.
About 10 minutes after that, the rocks stabilised and stopped flowing like a liquid. The titanic forces of impact sent shockwaves through the planet and caused earthquakes that would top the 10-point Richter scale, rattling the ground with greater force than any existing fault is capable of producing.
Despite flowing as if they were fluid, the rocks did not melt entirely. We’re not sure how this works, Gulick says.
“The vast majority of the rocks that we pulled up from the peak ring were never melted,” Gulick says. “But they obviously flowed to get there. Somehow, the shock wave, and all the fracturing and faulting, allows the rock to lose all its cohesion and actually be able to temporarily flow.”
“It is a great surprise that the rocks found in this drilling program are recognizably crystalline granite basement rocks showing much of the original structure,” writes Penny Barton at the University of Cambridge in an editorial accompanying the new work.
The findings are good news for studying the interiors of other planets – all we have to do to see inside them is check out the rims of craters.
“If you look at large impact craters on the rocky planets and you see these peak rings, those bits of topography are actually windows into the mid-crust,” Gulick says.
And the calamity may have had a silver lining here on Earth, Morgan says. Rocks in the asteroid’s path were riven by new cracks and pores, which made them less dense and would have allowed water to flow through them more readily.
“In these fractured, porous rocks, it’s possible for microbes to enter,” Morgan says. “Maybe things came back into the crater that were a bit exotic.”
Journal reference: Science, DOI: 10.1126/science.aah6561