The Next Species: The Future of Evolution in the Aftermath of Man Read Online Free Page B

the asteroid that got the dinosaurs at the Cretaceous extinction may have produced a better fireworks display and spectacular tsunamis, in terms of pure raw killing power, the Permian extinction can’t be beat. Its witch’s brew of toxins poisoned the land for several hundred thousand years. Doug Erwin says that the eruption of the Siberian Traps caused global cooling from the erupted dust, global warming from the CO 2 , and acid rains from billowing clouds of sulfur. Couple this with ocean acidification and the death of oxygen in the deep seas due to the melting of polar ice and the loss of ocean currents, and you have a lethal force that far exceeded the destruction caused by the falling asteroid during the Cretaceous.
    The resulting excess CO 2 entered the ocean, making the water acidic enough to prevent animals from forming exterior skeletons and destroying most of the reef-making organisms of the Permian seas and most of the reefs. The acidic nature of the seawater, coupled with the lack of oxygen in the deep oceans, wreaked havoc on marine plants and animals. The sulfates that emerged from the volcanoes reached the upper atmosphere, to be carried afar as sulfuric acid and lethal acid rains. These rains may have been strong enough, suggests Erwin, to kill off many of the terrestrial plants. This totally denuded landscapes over much of the earth’s surface. Scientists have found evidence that much of the rain that followed the Permian extinctions rolled off the land in flash floods, since there was no vegetation to contain the flow of water.
    Floods skipped across the earth like oil does on a hot skillet, moving in every direction, leaving braided gullies in the rock record. I’ve witnessed fast-moving desert flash floods that carved out chunks of road like butter, but desert rains are meager. Imagine flash floods raging in plant-free tropical or coastal environments where annual rainfalls are twenty, fifty, one hundred inches, or more, racing in full and furious force across landscapes stripped of vegetation, and you’ll get an idea of what the floods that followed the Permian extinction must have been like.
    But despite the evidence of multiple causes for the Permianextinction, some scientists still champion their favorite antagonists. Andrew Knoll, a paleontologist at Harvard, thinks that many of the catastrophes—their causes and their results—can be boiled down to one chemical compound, CO 2 , the biggest villain of the day, and perhaps our greatest threat as well.In a 2007 paper in Earth and Planetary Science Letters , Knoll and colleagues tried to work backwards from the extinction event, doing a computerized autopsy of the victims to see if the massacre matched the typical scenario caused by oxygen depletion, a breakdown of the food web, and acid rains, but none of them quite matched the autopsy except for CO 2 . He highlighted a gas that so many today ignore. “Only30 percent of the species of plants and animals were tolerant of massive doses of CO 2 . But after the Permian extinction, that 30 percent suddenly becomes 90 percent of all living animals.”
    Estimates vary on how long this extinction lasted. MIT’s Sam Bowring sets the duration at about sixty thousand years. The tiny chewing apparatuses of small eel-like animals are some of the first fossils to appear in layers of earth laid down after the Permian extinction. Fossils of Lystrosaurus , a mammal-like reptile that looked like a bulldog with tusks, but which survived the extinction and proliferated, mark the beginning of the Triassic recovery.
    The irony of the Permian extinction is that though it devastated large portions of the planet, it created opportunities in newly emptied terrain. From the resurrection of life after the mass annihilation of the Permian came more-adaptive species, changes in ecosystems, and a world more diverse than the one before it. Perhaps these improvements could be in our future—if we survive the extinction.
    The