Where Life Found Refuge During Mass Extinction Michael Reilly, Discovery News
Oct. 3, 2008 -- During the worst apocalypse the planet has ever known, somehow, life found a way to survive. But how? Scientists now think they have an answer: a nurturing refuge in the shallow continental shelf waters of northwestern Pangea. During the end of the Permian era 250 million years ago, global warming ran rampant on Earth, extinguishing 95 percent of life in the ocean, and 70 percent of life on land. Through the darkest days, the planet was a barren wasteland. Ocean circulation, so vital to our modern climate, had shut off. Huge algal blooms sucked the seas dry of oxygen. Poisonous hydrogen sulfide built up to lethal concentrations in the water and may have even been belched into the atmosphere, suffocating organisms on shore. The fossil record of the Permian-Triassic extinction is a stark one -- rocks go from teeming with life to nearly empty in the geologic blink of an eye. But searching through deposits left at the height of the extinction event, Tyler Beatty of the University of Calgary discovered something nobody ever expected to see: an almost fully-intact marine ecosystem. Amid the barren, empty sedimentary rocks Beatty found tracks left by hard-shelled arthropods, teeth from small fish, and the burrows of ancient crustaceans that would rival their modern descendants, lobsters, in size. "We see as many as 23 different genera of animals in some of these rocks. You'd be lucky to see that if you went out and scooped up a piece of the ocean floor today," Beatty said. How could such a lively ecosystem hang on while the rest of the world was dead or dying? Beatty thinks wave action and storms near the shore aerated the waters, mixing life-giving oxygen into the first 50 meters (160 feet) of ocean. "There's a pretty sharp break between where life is and isn't," Beatty said. Just a few meters deeper in the ancient ocean, and the number of genera (a category of life one level broader than species) plummets from 23 to one -- lethal conditions are back in full effect. "This is a healthy community living right next door to a very unhealthy one." Beatty calls this narrow band between the pounding surf of the shoreline and the noxious deep ocean the "habitable zone." He thinks he's seen evidence of it in several places outside the rocks of the Canadian Arctic, and believes life may have fled to the zone repeatedly in Earth's past to weather mass extinctions. "People have certainly had the thought that there would be refuges during mass extinctions," David Bottjer of University of Southern California said. "This is really the first time someone has made a good piece of science out of it." Juan Cole suggests: >So if humans do unalterably again poison the planet by digging oil and coal up out of the ground and pumping carbon dioxide into our atmosphere, apparently it will be we who get boiled and the lobsters that laze about all day snapping their pincers. < -- Jim Devine / "Nobody told me there'd be days like these / Strange days indeed -- most peculiar, mama." -- JL. _______________________________________________ pen-l mailing list [email protected] https://lists.csuchico.edu/mailman/listinfo/pen-l
