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


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As he talks, MacLeod holds up a bag of the shales, each 2- to 3-inch piece looking something like a misshapen barbecue briquette. "The motivation for the leg was actually to investigate the Late Cretaceous greenhouse climate," he says, "the warmest conditions the Earth has seen for the last 150 200 million years. These are actually some samples right here. They are really organic rich, and contain micro-fossils that are beautifully preserved. So the idea was to get samples that were so well preserved that you could, in effect, do chemical analyses of the ancient ocean."

MacLeod freely admits his chief area of expertise is not directly involved with asteroid strikes and their geological imprints. He's more into a group of giant clams, an ancient mollusk that, MacLeod discovered early in his career, actually faded from the fossil record well before the mass extinction, an episode known to geologists and paleontologists as the "K/T boundary event."

The boundary represents the 65-million-year-old line in the geological record indicating a dramatic break between an abundance of plant and animal species living during the Cretaceous (K) Period, and the disappearance of most of these same species during Tertiary (T) Period. It was the anomalous abundance of a rare element, iridium, at the K/T boundary that led a father-and-son team of scientists to surmise that an asteroid seeded the Earth with iridium during a mass extinction event.

"I was asked to sail because, to get to these rocks that are 90 million years old, you need to drill through the rocks that are 75 to 65 million years old, which goes right through my area of expertise and interest," MacLeod says. "There is a rule on these expeditions that, if an area hasn't been cored before, you have to core it and describe it. You're not allowed to just blow off everybody else's interests to get to the rocks you are interested in."

Because sediment cores from an earlier journey to Demerara had failed to show the K/T boundary, organizers of Leg 207 didn't bother to invite researchers specializing in the boundary event. The shock was palpable, MacLeod recalls, when the Resolution's drills yielded what is arguably the most pristine K/T boundary core ever recovered.

"We thought there would be a 3- to 5-million-year missing interval," MacLeod says. "As the core kept coming up we were all saying, 'Boy, we should be hitting that hiatus pretty soon.' Then it was, 'Oh, my goodness, we're within a million years of the boundary,' and then, 'It should be in the next core!'"

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Published by the Office of Research.

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