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 This list of trilobites is a comprehensive listing of all genera that have ever been included in the class Trilobita, excluding purely vernacular terms. The list includes all commonly accepted genera, but also genera that are now considered invalid, doubtful (nomina dubia , 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. 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." 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 (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 argon (är`gŏn) [Gr.,=inert], gaseous chemical element; symbol Ar; at. no. 18; at. wt. 39.948; m.p. −189.2°C;; b.p. −185.7°C;; density 1.784 grams per liter at STP; valence 0. . What do buckyballs and trapped gas have to do with asteroids This is a list of numbered minor planets, nearly all of them asteroids, in sequential order. As of late September 2007 there are 164,612 numbered minor planets, and many more not yet numbered. Most asteroids are ordinary and not particularly noteworthy. and mass extinction? "We know these structures were formed outside our solar system solar system, the sun and the surrounding planets, natural satellites, dwarf planets, asteroids, meteoroids, and comets that are bound by its gravity. The sun is by far the most massive part of the solar system, containing almost 99.9% of the system's total mass. ," Becker says. "The extreme temperature and pressure needed to forge these gases don't exist on Earth." The buckyball buckyball, colloquial term for buckminsterfullerene, a roughly spherical fullerene molecule consisting of 60 carbon atoms. Buckytube is a generic term for cylindrical fullerenes. gases also match those found in meteorite meteorite, meteor that survives the intense heat of atmospheric friction and reaches the earth's surface. Because of the destructive effects of this friction, only the very largest meteors become meteorites. 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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