Scientists think that 66 million years ago, a giant asteroid struck Earth near what is now the Gulf of Mexico, devastating the planet and wiping out the dominant form of life, the dinosaurs.
But what happened next?
University of Texas geophysics professor Sean Gulick has been spending significant chunks of the last two months on a makeshift rig 15 miles from the Mexican coast trying to answer that tricky question. Scientists have several strong hypotheses about the “dino doomsday” crater but surprisingly little hard evidence to prove specifics.
The energy released by the strike doesn’t fully explain the dinosaurs’ demise. It remains unclear which forms of life survived near the crater. Even the crater’s shape isn’t fully explained by the laws of physics as we understand them.
Gulick is co-leading a team of 33 scientists from 12 countries that has nearly finished gathering samples they hope will help test various theories using geology. From atop a rig resting on 250-foot-tall pillars, the crew has been drilling through the seafloor and down into the original crater.
“We’ve got dinosaurs and space,” he said. “Who doesn’t love that?”
Arriving at 76,000 mph
Gulick and co-lead researcher Joanna Morgan, a geophysics professor at Imperial College London, hope the material that Expedition 364 collects will contribute to more than just understanding how the dinosaurs died off. They hope it yields clues about what Earth could endure if an asteroid strikes — and clues that help in the search for life on other worlds.
Gulick describes the focus of the expedition with a single word: iridium.
The hard, brittle, silvery-white metal is common in asteroids. On Earth, it’s extremely rare, save for within a deep layer of clay above rocks that date back to the end of the Cretaceous period, when dinosaurs lived. Scientists think a meteor struck the Earth around that time hard enough to spread pieces of its iridium around the globe.
In the late 1980s, scientists began hypothesizing that the crater where the asteroid struck, which is now beneath millions of years of accumulated sediment, is in the Chicxulub (pronounced CHEEK-shoo-loob) region of Mexico and a portion of the Gulf. This is now the prevailing theory, which led Gulick and the expedition’s other scientists to the Yucatan Peninsula.
One mystery they are trying to help unravel is why the crater is shaped as it is. Many people think of craters as a large bowl in the ground. But that is only the smallest kind, Gulick said. The really big ones have a ring of mountains surrounding the middle.
These formations are explained partly by the combination of size and speed with which an asteroid hits. The asteroids come in so fast – 76,000 mph – and strike with such force that they essentially liquefy the rock and hurl it outward.
“These impacts,” Gulick said, “produce pressures that nothing in our experience does.”
In the case of the Chicxulub crater, the asteroid struck with the force of roughly 100 million atomic bombs, causing a 62-mile-wide swath of rock to “splash out” in a wave and then fall back in on itself. Morgan, the team co-leader, told The Guardian that an expanding plume of red-hot vapor could have vaporized everything in a circle reaching as far as Miami and Mexico City. That, she said, was probably followed by hurricane-force winds and a cloud of sediment that blocked out the sun.
The end result was a crater 125 miles across and nearly a mile deep.
Our understanding of physics cannot fully explain why that happened, Gulick said. One objective of the expedition is to find samples that, he hopes, will yield clues. Gulick, whose favorite dinosaur is the triceratops along with the marine reptile the plesiosaur, describes the other reasons for the expedition in terms of “the negative” and “the positive.”
Writer Gregg Easterbrook argues in a 2008 issue of The Atlantic magazine that mankind has been lucky. An asteroid strike is unlikely any time soon but possible, he contends. Strikes that happened relatively recently, in geological terms, hit over the ocean, rather than land.
“Near-Earth (comets and asteroids) are more numerous than was once thought, and … their orbits may not be as stable as has been assumed,” Easterbrook wrote.
Astronomers have identified 13,500 such “near-Earth objects” but generally guess there are double that number. Every hundred years or so, a small one hurtles into Earth’s atmosphere and explodes. They generally do little harm, but if one did explode over a town, Gulick said, “it could do major damage.”
Every hundred million years or so, an asteroid on the scale of the one that killed off the dinosaurs tends to strike.
“Probabilistically speaking, it’s something we’re not likely to see,” Gulick said. But if that likelihood is weighed against the catastrophic damage one could do, “it becomes something worth paying attention to.” Understanding the physics at work during a strike could help with whatever steps people could take in preparing for one, he said.
That understanding could also help determine what people would be dealing with after an asteroid strike. The energy released from the Chicxulub strike, though devastating, cannot fully explain why 75 percent of life on Earth went extinct. The prevailing theory is that dust and sulfates from the crater rose into the atmosphere, blocking out the sun and thus hampering photosynthesis, causing a collapse of the food chain. Another “kill mechanism” could have been the sulfur and carbon dioxide released falling back into the oceans, acidifying them.
If a sizable near-Earth object ever did begin bearing down on the planet, Gulick said, knowing that a massive cloud of carbon could soon rise into the sky could be crucial.
Gulick is quick to move on from the doomsday part, though.
The expedition has a blog, a Facebook page, a Reddit page and Twitter handle (#dinodoomsday) tracking its progress. Gulick does occasional online chats about the $10 million endeavor, which is funded by the International Ocean Discovery Program and the International Continental Scientific Drilling Program. Crew members, including UT geophysics professor Gail Christeson and postdoctoral paleontologist Chris Lowery, are renting houses along the coast. Gulick flies between the coast and his teaching duties in Austin.
The expedition is renting the Myrtle, a 100-foot-long lift boat that has extended its three thick pillars downward into the sea to perch on the crater’s inner peak ring. From that rig, team has hung the kind of drill used for offshore oil exploration. The crew has drilled down nearly a mile, taking a sample every 10 feet. Half the samples will be kept at Texas A&M University. The last day of drilling was May 25, and the expedition is now wrapping up.
The composition of the samples might reveal whether notable amounts of carbon were released by the strike. Pairing that knowledge with other information could help in assessing global climate change today, Gulick said.
But the tone of Gulick, who speaks in swift declarative sentences, takes on an additional note of enthusiasm when discussing another implication of the research.
Microorganisms moved into the rocks of the peak ring after the strike, according to samples so far. Labs in other parts of the world will sequence the DNA of those organisms and add that to the geological record.
How long did it take those organisms to inhabit the peak ring? How did they survive? What are they like?
On other planets, knowing what kinds of organisms can thrive around a crater – the dominant feature on the surface of planets such as Mercury and Mars – could help future interplanetary explorers search for life.
That is why the expedition includes an astrobiologist.
“Yes,” Gulick said, “that is a real job.”