A Johns Hopkins University graduate student may have solved a problem that has been baffling marine biologists and paleontologists for years: Why do coral reefs disappear from the fossil record during the beginning of the Cretaceous period -- 120 million years ago -- only to reappear after its end 35 million years ago?
The possible answer: Ancient seawaters low magnesium-to-calcium ratio during this interval made it difficult for the marine animals -- which build their skeletons from a mineral called aragonite calcium carbonate -- to grow and flourish into vast reefs. That left few to end up in the fossil record, posits doctoral candidate Justin Ries and his advisor Steven Stanley, professor in the Morton K. Blaustein Department of Earth and Planetary Sciences at the universitys Zanvyl Krieger School of Arts and Sciences.
"Scientists have grappled with this question for years, and my research shows that the answer is that the chemistry of Cretaceous seawater did not support the secretion of the aragonite mineral from which corals construct their skeleton," said Ries, who will present his research on Nov. 10 at the 116th annual meeting of The Geological Society in Denver. "Whats more, my experiments suggest that corals from the Cretaceous period almost certainly built at least part of their skeletons from calcite. This is groundbreaking, because it was previously believed that organisms do not generally change their skeletal mineralogy over time. Now we know that they do."
Lisa DeNike | EurekAlert!
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