Single impact killed the Dinosaurs

Via Drudge here:

A new study provides compelling evidence that "one and only one impact" caused the mass extinction, according to a University of Missouri-Columbia researcher.

"The samples we found strongly support the single impact hypothesis," said Ken MacLeod, associate professor of geological sciences at MU and lead investigator of the study. "Our samples come from very complete, expanded sections without deposits related to large, direct effects of the impact – for example, landslides – that can shuffle the record, so we can resolve the sequence of events well. 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. 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 his co-investigators studied sediment recovered from the Demerara Rise in the Atlantic Ocean northeast of South America, about 4,500 km (approximately 2,800 miles) from the impact site on the Yucatan Peninsula. Sites closer to and farther from the impact site have been studied, but few intermediary sites such as this have been explored.