Study: Single impact killed the dinosaurs

COLUMBIA, Mo., Nov. 30 (UPI) -- A U.S. researcher says he's obtained compelling evidence that one and only one meteor impact caused the mass extinction of the dinosaur.

Dinosaurs -- along with the majority of all other animal species on Earth -- became extinct approximately 65 million years ago. Some scientists believe the impact of a large meteor in the Yucatan Peninsula caused the mass extinction, while others argue there must have been additional impacts or other stresses about the same time.

Now University of Missouri-Columbia Associate Professor Ken MacLeod and colleagues say their research strongly supports the single impact hypothesis.

"What we see is a unique layer composed of impact-related material precisely at the level of the disappearance of many species of marine plankton that were contemporaries of the youngest dinosaurs," said MacLeod. "We do not find any sedimentological or geochemical evidence for additional impacts above or below this level, as proposed in multiple impact scenarios."

MacLeod and co-investigators Donna Whitney of the University of Minnesota, Brian Huber from the Smithsonian National Museum of Natural History, and Christian Koeberl of the University of Vienna recently reported their findings in the online version of the Geological Society of America Bulletin.