Tag Archives: extinction

Are We Causing the Sixth Extinction?

30 Jul

Elizabeth Kolbert in The New Yorker, 2009:

Over the past half-billion years, there have been at least twenty mass extinctions, when the diversity of life on earth has suddenly and dramatically contracted. Five of these—the so-called Big Five—were so devastating that they are usually put in their own category. The first took place during the late Ordovician period, nearly four hundred and fifty million years ago, when life was still confined mainly to water. Geological records indicate that more than eighty per cent of marine species died out. The fifth occurred at the end of the Cretaceous period, sixty-five million years ago. The end-Cretaceous event exterminated not just the dinosaurs but seventy-five per cent of all species on earth.

The significance of mass extinctions goes beyond the sheer number of organisms involved. In contrast to ordinary, or so-called background, extinctions, which claim species that, for one reason or another, have become unfit, mass extinctions strike down the fit and the unfit at once. For example, brachiopods, which look like clams but have an entirely different anatomy, dominated the ocean floor for hundreds of millions of years. In the third of the Big Five extinctions—the end-Permian—the hugely successful brachiopods were nearly wiped out, along with trilobites, blastoids, and eurypterids. (In the end-Permian event, more than ninety per cent of marine species and seventy per cent of terrestrial species vanished; the event is sometimes referred to as “the mother of mass extinctions” or “the great dying.”)

Once a mass extinction occurs, it takes millions of years for life to recover, and when it does it generally has a new cast of characters; following the end-Cretaceous event, mammals rose up (or crept out) to replace the departed dinosaurs. In this way, mass extinctions, though missing from the original theory of evolution, have played a determining role in evolution’s course; as Richard Leakey has put it, such events “restructure the biosphere” and so “create the pattern of life.” It is now generally agreed among biologists that another mass extinction is under way. Though it’s difficult to put a precise figure on the losses, it is estimated that, if current trends continue, by the end of this century as many as half of earth’s species will be gone.

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Nearly one-tenth of hemisphere’s mammals unlikely to outrun climate change: study

15 May

It’s not just about us. It’s about all the animals and plants in the biosphere.

For the first time a new study considers whether mammals will actually be able to move to those new areas before they are overrun by climate change. Carrie Schloss, University of Washington research analyst in environmental and forest sciences, is lead author of the paper out online the week of May 14 in the Proceedings of the National Academy of Sciences.

“We underestimate the vulnerability of mammals to climate change when we look at projections of areas with suitable climate but we don’t also include the ability of mammals to move, or disperse, to the new areas,” Schloss said.

Indeed, more than half of the species scientists have in the past projected could expand their ranges in the face of climate change will, instead, see their ranges contract because the animals won’t be able to expand into new areas fast enough, said co-author Josh Lawler, UW associate professor of environmental and forest sciences.

via Nearly one-tenth of hemisphere’s mammals unlikely to outrun climate change: study.