The enormous meteor that smashed into Mexico's Yucatan peninsula 65 million years ago didn't deal a death blow to the dinosaurs, a new study declares. Based on a close examination of sediment layers from that epoch, a team of researchers led by Gerta Keller has previously argued that the Chicxulub impact happened 300,000 years before the mass extinction known as the Cretaceous-Tertiary extinction event. Now, Keller has found supporting evidence that the impact had little immediate effect on the planet's biome. Says Keller:
"It didn't kill the dinosaurs. In fact, it didn't cause much damage that we can determine from the geological record" [The Scientist].
Since the 112-mile-wide Chicxulub crater was discovered in 1978, many researchers have come to believe that the massive impact caused clouds of dust to shroud the earth, cooling the planet and killing the dinosaurs along with many other species. But Keller's new study, to be published in the
Journal of the Geological Society,
offers a serious challenge to that theory. The researchers examined sandstone layers at a Mexico site about 750 miles from the crater, focusing on the fossilized plankton species present in the rock directly below and above a thin layer of iridium. The layer of that mineral, which is common in asteroids, marks the time of the impact. They found 52 species of plankton below the line--
and above the line after the impact the same 52 species were abundant. “We found not a single species went extinct as a result of the Chicxulub impact,” says Keller. This means the Chicxulub impact couldn’t have been the sole event causing the extinction, she says [Nature blog].
These
species samplings are not, of course, conclusive, and plenty of other surveys since 1978 do tie the extinctions closely to the asteroid. But since the new digs were so close to ground zero, the immediate species loss ought to be have been — if anything — greater there than anywhere else in the world. Instead, the animals seemed to escape unharmed [Time].
Still, many researchers are not convinced by Keller's findings, and some suggest that the ocean could have buffered the impact's effect on marine species like the plankton that Keller studied, causing a delay of several thousand years (a blink of an eye, in geological time) before extinctions began to occur. Keller, however, is already moving on to the next question: If an asteroid strike didn't kill the dinosaurs, what did? Her team believes that some
kind of atmospheric haze might indeed have blocked the sun, making the planet too cold for the dinosaurs — it just didn't have to have come from an asteroid. Rather, they say, the source might have been massive volcanoes, like the ones that blew in the Deccan Traps in what is now India at just the right point in history [Time].
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