Thursday, June 19, 2008

The size of the ocean can determine Earth’s biology

For years scientists have been trying to find explanations for some of the world’s most mysterious extinction events. Since life began on Earth some 3.5 billion years ago, there have been as many as 23 mass extinction events. Over the past 540 million years, there have been five well-documented mass extinctions, primarily of marine plants and animals, with a stunning 75-95 percent loss of species. Sometimes scientists have been able to pin down the likely culprits for these dramatic events, but often, no clear answer has ever been determined…at least not until now.

Recent research suggests that the size of the ocean itself has been one of the most constant and relentless decider of fates over the last 500 million years. Shanan Peters, lead author of the study, says that sea level has been, and will continue to be, one of the most influential factors in determining Earth’s biology.

Peters' research, which recently appeared in the journal Nature, provides an intriguing perspective on one of nature’s most pervasive mysteries. Most of us correlate Earth's periodic mass extinctions with dramatic and sudden events like a blazing asteroid or a sky-blackening super volcano—the kind of things that have been linked to the demise of the dinosaurs. While dramatic events like these do appear to have played major roles in some extinction periods, they certainly haven’t accounted for all of them. Peters says that is where sea level comes into play. His research provides evidence that convincingly fills in the gaps.

“The oceans might seem to be rather static, but sea levels, in fact, change quite dramatically over geological time. In fact, the rocks right here in Madison, Wisconsin—pretty much in the center of our continent—were in fact deposited in one of these shallow seas that covered much of the present day land area almost 500 million years ago…My results show that the expansion and contraction of these sea waves had a big impact on controlling which animals lived and which animals died…When these seas expand and contract, many of the animals that lived in them were forced to deal with all sorts of environmental changes, and many of those changes caused some animals to go extinct.”

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