WASHINGTON (AP) — Researchers have found evidence that a comet or space rock smashed into Earth 56 million years ago, perhaps setting off a massive warming that began around that time.
It's a suggestion that is causing much debate among scientists, many of whom question the link. Researchers study the mysterious ancient warming to better understand current man-made climate change and Earth's future.
About 56 million years ago Earth warmed by about 9 to 14 degrees (5 to 8 degrees Celsius) and then returned to normal, all in about 100,000 years. This helped lead to some extinctions and the rise of mammals. Theories about the cause have pointed to increased carbon in the atmosphere from many erupting volcanoes; a Greenland volcano that cooked a huge coal deposit; and sudden methane releases from underwater. But a new study in the journal Science suggests a link to a cosmic crash.
At the same time Earth started getting hotter, it seems to have been hit by a space object that sent debris flying around North America and maybe around the world, according to an examination of soil cores in New Jersey and Florida. The scientists didn't find the space rock or comet or a crater; instead, they found what they said were nearby rocks super-heated by the crash.
Study lead author Morgan Schaller, an Earth sciences professor at Renssalaer Polytechnic Institute, isn't quite saying the crash caused the massive carbon jump and the warming, but it's awfully suspicious timing, he said.
"We're saying this is really a remarkable coincidence," Schaller said. "We need to look into this much more closely."
However, study co-author Dennis Kent, a professor of at geological sciences at Rutgers University and Columbia University, wrote in an email that there could be, somewhere, an impact crater that he called the "ground zero" of the warming event.
Schaller's team was looking at sediment cores from two spots in New Jersey and one off Florida from 56 million years ago, looking for a certain small fossils, when they kept seeing tiny glass and crystal objects. They are about .004 inches long (100 microns), sometimes in spheres and sometimes in teardrops. They all showed signs of having the unique chemical signature of quartz that was shocked by a super-hot event.
It's the tell-tale signature of debris from a comet or asteroid vaporizing just as hits Earth, Schaller said. And they come from the exact same time period as sediment cores of the massive warming — known as the Paleocene-Eocene Thermal Maximum or PETM.
Schaller said so far his team hasn't found where the crater would be, or even how big an object it was or what kind of crater it would have caused.
Somehow the cosmic collision was strong enough to throw lots of carbon in the atmosphere, Schaller said. And scientists know that carbon dioxide and methane act as heat-trapping blankets, said Mark Boslough, a physicist at Sandia National Lab who studies both asteroid collisions and climate change but wasn't part of the study.
Several scientists said the study is off base, while quite a few others praised it.
Bruce Simonson at Oberlin University called study "new and exciting" with Schaller making a strong case that the spheres and teardrops are from an impact that hadn't been known before.
But four other experts said there was no way that a crash like this could be responsible for the carbon in the air and the heating that followed. They said other work contradicts Schaller's findings.
Carbon could not have gotten in the air as rapidly as needed under the Schaller scenario and the amount of carbon released into the air from a crash is "not even a small fraction" of the huge amount needed to trigger warming, said James Zachos at University of California, Santa Cruz.
A simpler and more reasonable explanation is that a massive number of volcanoes erupted, including ones in Greenland that heated up a coal field and released a lot of carbon dioxide, said Andy Ridgwell at the University of California, Riverside and the University of Bristol in England.
Follow Seth Borenstein at http://twitter.com/borenbears and his work can be found at http://bigstory.ap.org/content/seth-borenstein