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 World's End. Story by Charles E. Reineke.

 

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With his co-investigators, Donna L. Whitney of the University of Minnesota, Brian T. Huber of the Smithsonian's Museum of Natural History and Christian Koeberl of the University of Vienna, MacLeod examined a series of uniquely telling sediment samples recovered from deep within the Demerara Rise, a plateau located in one to 2-mile deep waters off the coasts of Surinam and French Guyana. Their analysis of the samples, published last January in the Geological Society of America Bulletin, provides compelling support for the idea that, for almost every species alive on that terrible day, a single asteroid brought near instantaneous extinction.

"The samples we found strongly support the single impact hypothesis," MacLeod said shortly after the study's publication. "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, 43, is a hale, square-jawed man who, by appearances, might just as easily be moving earth as studying it. He describes the expedition that led to his Demerara discovery -- eight weeks aboard the 470-foot JOIDES Resolution, a former oil exploration ship refitted for scientific use -- with the gusto of a seasoned sailor. "It's an incredible boat," he says, one that has virtually everything an ocean-going earth scientist could want.

The Resolution, named in part for its sponsor, the Texas A&M-based Joint Oceanographic Institutions for Deep Earth Sampling project, is indeed an impressive vessel. Its drilling derrick, towering some 200 feet above the waterline, allows the ship to deploy about 30,000 feet of pipe. Sixteen side-thrusters keep the vessel on site even in heavy seas. After samples are brought onboard, the Resolution's seven stories of laboratory space allow scientists to conduct detailed examinations of rock and sediment cores. On any given journey, the Resolution provides berths and board for some 100 crew members and 30 scientists working on dozens of projects. For this particular cruise, Leg 207, nobody was thinking much about single impacts and mass extinctions. Instead, MacLeod says, the chief goal was to retrieve and examine fossil-rich black shale that is found in abundance beneath the Demerara Rise.

       
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Published by the Office of Research.

©2007 Curators of the University of Missouri. Click here to contact the editor.