At the end of the Cretaceous era, a large meteorite ploughed into what is now Mexico's Yucatan Peninsula. The collision set off a chain reaction of environmental calamities that likely contributed to the demise of the dinosaurs. New research is now adding to the list of ensuing catastrophes, suggesting the collision cracked our planet's seafloor like an egg, forcing magma to pour out along the ocean's tectonic ridges.
New research published this week in Science Advances suggests the impact of the Chicxulub meteor spawned large seismic waves that coursed through the planet, reaching mid-oceanic ridges where tectonic plates rub against each other. This triggered intense volcanic activity across the Earth's ocean floor, and the release of magma trapped beneath the crust. This happened around the globe, extending for tens of thousands of kilometres along the mid-ocean ridges. The lead authors of the new study, Joseph Byrnes and Leif Karlstrom from the University of Oregon, say the ensuing global volcanism was likely a contributing factor to the mass extinction that followed.
During a short span of time some 66 million years ago, three out of every four species of plants and animals disappeared off the face of our planet. This event, known as the Cretaceous-Tertiary (KT) mass extinction, happened around the same time that the 15km-wide Chicxulub meteor smashed into Earth. Naturally, many scientists say the collision contributed to the demise of the dinosaurs, in which a prolonged "impact winter" made it difficult for animal and plant life to survive.
But it just so happens that another catastrophic event was going on elsewhere at the same time: The volcanic Deccan Traps of India. Gases released by these eruptions may have altered the Earth's climate, resulting in the mass extinction.
So we have some scientists saying it was the asteroid that made the dinos go extinct, some saying it was caused by these massive lava flows, and some saying it was a combination of the two. But what if the two were somehow related? This latest research from the University of Oregon suggests a possible link in the form of severely disturbed tectonic systems.
Byrnes and Karlstrom aren't the first to link the Chicxulub meteor to the Deccan Traps. Back in 2015, a team led by professor Paul Renne from the University of California at Berkeley concluded that seismic waves produced by the meteorite impact influenced volcanoes far away, including those in the Deccan Traps. The collision didn't create the Deccan Traps - these volcanic eruptions began long before the asteroid struck - but it could have accelerated and amplified the lava flows and outpouring of gases. In other words, it may have made a bad thing much worse. The new study expands upon this research, showing that other tectonic systems were affected by the Chicxulub event.
Global spread of mid-ocean ridges. Colours indicate maximum gravity anomalies. (Credit: Joseph Byrnes)
Using publically available datasets, Byrnes and Karlstrom used gravity to track changes in ancient crust deep beneath the seafloor. These findings were corroborated by looking at maps of ocean floor topography and tectonic spreading rates. But it was the gravitational anomalies that served as the smoking gun.
The researchers chopped up the seafloor into one million-year-old sections that date back 100 million years. At the 66 million year mark - when the meteorite struck - the researchers documented evidence of short-lived magma bursts along ancient ocean ridges. The presence of these magma bursts coincided with "free-air gravity" anomalies shown in the data. Free-air gravity anomalies are variations in gravitational strength that can be detected from satellites. It's a neat way of detecting differences in mass, which in this case was used to detect chunks of excess matter buried under the ocean floor. The elevated marine gravity weirdness, say the authors, was caused by the new magma swelling up after the Chicxulub collision, and that there was heightened volcanic activity at the mid-ocean ridge at the time of the impact. Byrnes and Karlstrom aren't saying this increase in volcanism is what killed the dinosaurs, but it should be considered a factor in future investigations.
Credit: Joseph Byrnes
"This study is important because it validates the implicit prediction we made in 2015, that the Chicxulub impact affected not only the existing Deccan Traps magma system, but would have affected other existing magma systems as well," Paul Renne, who wasn't involved with the new study, told Gizmodo. "Byrne and Karlstrom very cleverly decided to test this by looking at the globe-encircling mid-ocean ridge system, which is always volcanically active at fairly consistent rates. This means that any short-term anomalies would really stand out if you know what to look for. What they found is pretty clear evidence that there was a sudden surge in undersea volcanism right at the same time as the impact."
Sankar Chatterjee, a professor of geosciences at the Museum of Texas Tech University, said the paper "is very well-written" and that the authors "suggest an interesting geodynamic correlation during the [Cretaceous-Tertiary (KT) mass extinction] event". But Chatterjee doesn't buy the connection between the observed rise in volcanism to the Chicxulub impact.
"Unfortunately, around the Chicxulub crater, the volcanic activity is practically absent except the impact melt rock in the target rock of the crater basin," he told Gizmodo. "One should expect massive volcanism in the Gulf of Mexico, if Chicxulub was the culprit for far away volcanism."
Chatterjee pointed to the work of Renne and others who have suggested that intense Deccan volcanism in India around the time of the KT mass extinction was caused by the Chicxulub impact. But he believes another asteroid, one that formed the Shiva crater off the west coast of India, contributed to the Deccan Traps.
"Are these events coincidental or causal? We don't know," he said. "To me, the Shiva impact we proposed earlier at the western shelf of India may be a better candidate to explain both of these volcanic phenomena because of geographic proximity. The Shiva was larger and much more catastrophic than the Chicxulub. The authors built their case meticulously, but to me the impact and mid-ocean volcanism looks tenuous at best."
To be fair, the Shiva crater is not recognised as an official crater by scientists, and it remains a controversial possibility. But Chatterjee's point about the connection between the Chicxulub impact and the apparent increase in global volcanism not being very well established (aside from it happening at roughly the same time) is valid. In future, it would be good to see researchers explore and model the ways in which a large asteroid could create the effects described in the new study.