The massive asteroid impact that killed the dinosaurs also triggered mega-earthquakes that lasted months.
Around 66 million years ago, an asteroid approximately 6.2 miles (10 kilometers) across smashed into Earth near the Yucatan Peninsula, plunging the planet into darkness and causing a mass extinction that wiped out 80% of animal life — including all the non-avian dinosaurs.
The tremendous mega-quake caused by the collision left its mark in rocks around the Gulf of Mexico, according to new research presented Sunday (Oct. 9) at the annual meeting of the Geological Society of America (GSA).
Hermann Bermúdez, a geology doctoral student at Montclair State University in New Jersey, discovered rock layers in Colombia, Mexico, Texas, Alabama and Mississippi that are deformed and cracked as a result of the quake, and some that are filled with rubble left behind by giant tsunamis generated by the impact.
Some of these twisted and rumpled layers also hold evidence of pollen — a sign that vegetation began to recover at least six months after the impact, Bermúdez told Live Science. The fact that these layers are deformed even as plants were making a comeback shows that the quakes triggered by the impact lasted months.
Dino-killing power
The Chicxulub impact — named for the community on the Yucatán Peninsula near the crater left by the space rock — was mind-bogglingly powerful. When the chunk of asteroid slammed into Earth about 66 million years ago, it released the energy equivalent to 10 billion Hiroshima bombs and left a 110-mile-wide (180 km) crater, Bermúdez said. The seismic energy was 50,000 times greater than that produced by the devastating 2004 Sumatra earthquake. The impact triggered earthquakes with magnitudes over 11; for comparison, the most powerful quake on the human record was 9.5 magnitude in Chile in 1960. The Chicxulub impact also triggered tsunamis with waves over a mile high.
There have been scattered reports of scars that the cataclysmic event left in the rock record, Bermúdez said, but most of these descriptions are relatively sparse. In 2014, he discovered a layer of rock on Colombia's Gorgonilla Island speckled with tiny glass beads called tektites and microtektites, which formed when melted rock was flung into the atmosphere by the impact and then rained down in a cooled, spherical form after the event.
The Gorgonilla discovery spurred Bermúdez to look for other evidence of that disastrous day using what he called "old-school geology," or on-the-ground fieldwork using just "a hammer, a map, our boots, a hat, et cetera," he said in his GSA presentation in Denver on Sunday.
Evidence of ruin
In northeastern Mexico, at the Brazos River in Texas, and at several sites in Alabama and Mississippi, Bermúdez, guided by local geologists, investigated rock layers dating to around the time of the impact, known as the Cretaceous-Paleogene (K-Pg) boundary. He found the fingerprints of the impact: faults, fractures, mixtures of debris and mudstone that indicate the passage of a tsunami. Some layers showed signs of liquefaction — a phenomenon that can occur in waterlogged sediments during large earthquakes, when the shaking essentially causes the ground to lose its strength and behave as a liquid.
All of the rocks studied by Bermúdez were on the seafloor when the impact occurred. Evidence on Gorgonilla Island revealed that the upheaval lasted a long time after the initial impact: Fern spores that gradually drifted to the seafloor days to weeks after being released by the plants appear in a layer just 0.4 inch (1 centimeter) above the K-Pg boundary. That layer is rumpled and deformed.
"It was shaking when these deposits were settling on the seafloor," Bermúdez told Live Science. Because ferns didn't recover for six months to a year after the Chicxulub impact, the finding indicates that the planet kept shuddering for months after the asteroid slammed into it.
Bermúdez will return to Mexico this week to conduct more fieldwork, he said. He hopes to estimate the magnitude of the post-Chicxulub megaquake from the rock record.
