It’s official: Yucatan asteroid killed the dinosaurs
More than 65 million years ago, an asteroid 10 kilometers in diameter slammed into the Yucatan Peninsula in Mexico with an explosive force one billion times more powerful than the atomic bomb at Hiroshima. Tsunamis up to 300 meters high and earthquakes that would have scored more than 10 on the Richter scale tore through the area. Impact temperatures alone would have killed every living thing for thousands of miles, but was this terrible event enough to trigger the KT extinction, one of the three largest mass extinctions in the history of the planet?
A team of more than 30 scientists, including UAF’s Michael Whalen, have concluded that it did. They reported their findings in the March 5 issue of “Science”. The researchers studied more than 20 years of data to see if the massive asteroid impact, known as the Chicxulub impact, could have caused the mass extinction of the dinosaurs. The extinction is believed to have occurred quickly at the end of the Cretaceous period.
For 30 years, scientists have debated the cause of the KT extinction. That the asteroid collision happened at about the same time is not disputed but many have argued that a single event would not have had such a dramatic worldwide impact. Some scientists have hypothesized that the extinction was the result of long-term volcanic eruptions in India.
Whalen’s team looked at the geologic rings of drilled core samples from the side of the crater and elsewhere. One ring in particular, the boundary between the Cretaceous and Paleocene periods, marked the change in sedimentation from before and after the extinction event. They compared this to what the boundary might look like in different catastrophic scenarios.
“It’s the single most studied stratigraphic boundary anywhere in the world,” said Whalen, an associate professor of geology who studies sedimentation.
Although some scientists believe long-term volcanic eruptions caused the extinction event, Whalen’s team found that the boundary contained high levels of iridium. This substance is more common in space than in volcanoes. According to Whalen, much of the debate stems from a reluctance to believe that “something outside of the Earth could have this big of an effect on the Earth.”
Scientists have long wondered why so few dinosaur species survived the impact. Patrick Druckenmiller, the curator of earth sciences at the UA Museum of the North, said one thing we don’t know is whether the dinosaurs were thriving when they went extinct, or whether their populations were already declining.
Druckenmiller studies high latitude reptiles, which, he said, should have been able to adapt to the asteroid’s aftermath. But he said the conditions would have been challenging for even the hardiest of species. Atmospheric gases would have acidified oceans. Dust kicked up by the impact would have blocked sunlight, hampering the photosynthesis that sustains food chains.
Some species did survive, of course, and went on to repopulate the planet. Druckenmiller said that one group of dinosaurs, the Therapods, eventually evolved into modern birds. Lemming-sized mammals also survived. Although bird ancestors and mammals were both small, size was not the only factor in surviving the extinction. Dinosaurs such as the velociraptor, only a couple feet tall, also did not survive. Lizards and turtles survived, so warm blood was not the only factor. Druckenmiller said there might not have been clear groups that were more suited for survival. “Sometimes, things have to do with pure chance,” he said.