Megadeath.More than 250 million year's ago, something--until now, no one knew what--wiped out more than 70 percent of Earth's land dwellers and 90 percent of its ocean species. This included trilobites trilobite (trī`ləbīt'), subphylum of the phylum Arthropoda that includes a large group of extinct marine animals that were abundant in the Paleozoic era. They represent more than half of the known fossils from the Cambrian period., soft-shelled sea creatures that crawled on the ocean floor--perhaps the most populous species of the time. Earth's worst mass extinction mass extinction, the extinction of a large percentage of the earth's species, opening ecological niches for other species to fill. There have been at least ten such events. The five greatest were those of the final Ordovician period (approximately 435 million years ago), the late Devonian period (357 million years ago), the final Permian period (250 million years ago), the late Triassic period (198 million years ago), and the final Cretaceous was so catastrophic it's dubbed "the Great Dying." For years scientists have puzzled over the disaster's cause. Many suspected a high-speed comet or asteroid collision with Earth as the culprit. But unlike the space object that probably annihilated dinos 65 million years ago--and left a huge crater hidden beneath the Gulf of Mexico--there was no evidence to support the theory for the earlier extinction. That is, until University (if Washington researcher Luann Becker found the "smoking gun Smoking Gun Something that serves as indisputable evidence or proof, especially of a crime.Notes: Here is an example used in everyday language from CNN.com on Feb 6, 2002:"Maybe there was no proof before, but there is now a secret memo - personally handed to [U.S. Vice-President Dick] Cheney by Ken Lay [ex-Enron chairman and CEO], which helps explain why the White House is so skittish about Enron and why Cheney and [U.S.." Last February, Becker and her team announced evidence linking a giant asteroid or comet to the extinction. Embedded in 250-million-year-old rock samples found in China and Japan are soccer ball-shaped molecules called buckyballs A molecule of carbon expected to have use in a variety of applications, especially in the medical field. Also known as "Fullerines" because the 60 atoms that make up their spherical molecule resemble Buckminster Fuller's geodesic domes, they are lighter than plastic and stronger than steel. They can also conduct heat and electricity. Buckyballs were identified in 1985 by three scientists who later received a Nobel prize for the discovery. (named after scientist Buckminister Fuller, who discovered them). Trapped inside the molecules are vital clues to the mystery: two extraterrestrial gases, rare forms of helium and argon. What do buckyballs and trapped gas have to do with asteroids and mass extinction? "We know these structures were formed outside our solar system," Becker says. "The extreme temperature and pressure needed to forge these gases don't exist on Earth." The buckyball gases also match those found in meteorite samples, as well as gases found in deep soil layers linked to periods of extinction. Far from gloom and doom, Becker believes comet collisions with Earth lend a helping hand to evolution, the process by which living things adapt to their environment. "It's as if life learns a lesson from what happened and comes back much more prepared to handle extreme conditions," she says. 5 WORST MASS EXTINCTIONS YEARS AGO (in millions) Cretaceous-Tertiary (dinosaurs) 65 End Triassic 199 to 214 Permian-Triassic (the Great Dying) 251 Late Devonian 364 Ordovician-Silurian 439 Source: Smithsonian Institution's National Museum of Natural History |
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