http://www.newyorker.com/reporting/2009/05/25/090525fa_fact_kolbert http://archives.newyorker.com/?i=2009-05-25#folio=053">Elizabeth Kolbert, A Reporter at Large, “The Sixth Extinction?,” The New Yorker, May 25, 2009, p. 53
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http://archives.newyorker.com/?i=2009-05-25#folio=053">Read the full text of this article in the digital edition. (Subscription required.)
ABSTRACT: A REPORTER AT LARGE about the sixth mass extinction. Describes how graduate student Karen Lips observed the mysterious disappearance of large numbers of local golden frogs, in the nineteen-nineties, at several locations in Panama and Costa Rica. Whatever was killing Lips’s frogs moved east, like a wave, across Panama. Of the many species that have existed on earth, more than ninety-nine per cent have disappeared. Yet extinction has been a much contested concept. Throughout the eighteenth century, the prevailing view was that species were fixed. Charles Darwin believed extinction happened only slowly, but he was wrong. Over the past half billion years, there have been at least twenty mass extinctions. Five of these—the so-called Big Five—were so devastating that they’re usually put in their own category. The fifth, the end-Cretaceous event, which occurred sixty-five million years ago, exterminated not just the dinosaurs but seventy-five per cent of all species on earth. Once a mass extinction occurs, it takes millions of years for life to recover, and when it does it’s generally with a new cast of characters. In this way, mass extinctions have played a determining role in evolution’s course. It’s now generally agreed among biologists that another mass extinction is under way. If current trends continue, by the end of this century as many as half of earth’s species will be gone. The writer went frog collecting in Chagres National Park with Edgardo Griffith, the director of EVACC (the El Valle Amphibian Conservation Center). About two decades ago, researchers first noticed something odd was happening to amphibians. It’s difficult to say when the current extinction event—sometimes called the sixth extinction— began. Its opening phase appears to have started about fifty thousand years ago, when the first humans migrated across Australia and America. The main culprit in the wavelike series of amphibian crashes is a chytrid fungus, known as Bd. At this point, Bd appears to be unstoppable. Mentions Don Nichols, Allan Pessier, Joyce Longcore, and Rick Speare. In the fossil record, mass extinctions stand out. Mentions Walter Alvarez and the Alvarez hypothesis, which wreaked havoc with the uniformitarian idea of extinction. In 2007, biologist Al Hicks, of the New York State D.E.C., and the National Wildlife Health Center started investigating a series of mysterious bat deaths. Many of the dead bats were discovered with a white substance on their nose, which was cultured and found to be an unidentified fungus. Mentions White-Nose Syndrome (W.N.S.). The writer visited an abandoned mine to study bats with Hicks. One of the puzzles of mass extinction is why, at certain junctures, the resourcefulness of life seems to falter. Just in the last century, carbon dioxide levels in the atmosphere have changed by as much as they normally do in a hundred-thousand-year glacial cycle. In the end, the most deadly aspect of human activity may simply be the pace itself.
http://www.motherjones.com/environment/2007/05/gone Gone: Mass Extinction and the Hazards of Earth's Vanishing Biodiversity
By the end of the century, half of all species on Earth may be extinct due to global warming and other causes. Who will survive the world's dwindling biodiversity, and why?
—By Julia Whitty
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IN THE FINAL STAGES OF DEHYDRATION the body shrinks, robbing youth from the young as the skin puckers, eyes recede into orbits, the tongue swells and cracks. Brain cells shrivel and muscles seize. The kidneys shut down. Blood volume drops, triggering hypovolemic shock, with its attendant respiratory and cardiac failures. These combined assaults disrupt the chemical and electrical pathways of the body until all systems cascade toward death.
Such is also the path of a dying species. Beyond a critical point, the collective body of a unique kind of mammal or bird or amphibian or tree cannot be salvaged, no matter the first aid rendered. Too few individuals spread too far apart or too genetically weakened are susceptible to even small natural disasters. A passing thunderstorm. An unexpected freeze. Drought. At fewer than 50 members, populations experience increasingly random fluctuations until a kind of fatal arrhythmia takes hold. Eventually, an entire genetic legacy, born in the beginnings of life on Earth, is smote from the future.
Scientists recognize that species continually disappear at a background extinction rate estimated at about one species per million species per year, with new species replacing the lost in a sustainable fashion. Occasional mass extinctions convulse this orderly norm, followed by excruciatingly slow recoveries as new species emerge from the remaining gene pool until the world is once again repopulated by a different catalog of flora and fauna. From what we understand so far, five great extinction events have reshaped Earth in cataclysmic ways in the past 439 million years, each one wiping out between 50 and 95 percent of the life of the day, including the dominant lifeforms, the most recent event killing off the non-avian dinosaurs. Speciations followed, but an analysis published in Nature showed that it takes 10 million years before biological diversity even begins to approach what existed before a die-off.
Today we're living through the sixth great extinction, sometimes known as the Holocene extinction event. We carried its seeds with us 50,000 years ago as we migrated beyond Africa with Stone Age blades, darts, and harpoons, entering pristine Ice Age ecosystems and changing them forever by wiping out at least some of the unique megafauna of the times, including, perhaps, the saber-toothed cats and woolly mammoths. When the ice retreated, we terminated the long and biologically rich epoch sometimes called the Edenic period with assaults from our newest weapons: hoes, scythes, cattle, goats, pigs.
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You probably had no idea. Few do. A poll by the American Museum of Natural History finds that 7 in 10 biologists believe that mass extinction poses a colossal threat to human existence, a more serious environmental problem than even its contributor, global warming, and that the dangers of mass extinction are woefully underestimated by most everyone outside of science. In the 200 years since French naturalist Georges Cuvier first floated the concept of extinction, after examining fossil bones and concluding "the existence of a world previous to ours, destroyed by some sort of catastrophe," we have only slowly recognized and attempted to correct our own catastrophic behavior.
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