Word: fossils
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Dates: during 1980-1989
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Around the time of the mass extinction, the fossil site was apparently in a 300-mile-long rift valley fringed with high mountains. The climate swung between wet and dry spells every 20,000 years or so, leaving telltale alternating layers of lake sediments and sandstone visible on the present-day cliffs. "When it rained," says Olsen, "chunks of rock and mud raced down the mountainsides and buried large swaths of ground." Many of the now fossilized animals escaped the slides, only to be trapped in cracks that opened as the mud flow dried and shrank. Olsen believes the animals...
...fossil find may have implications for the controversial theory proposed by a team headed by Physicist Luis Alvarez and his son Geologist Walter Alvarez, both of the University of California, Berkeley. In their view, at least some of the great extinctions, especially the one that wiped out the dinosaurs 65 million years ago, were caused by the effects of giant comets or asteroids smashing into the earth. The impacts, they suggest, spewed debris into the atmosphere, obscuring the sun, causing temperatures to drop and bringing on a long "winter" that killed much of the life on earth. But, at least...
...Triassic-Jurassic extinction, however, that evidence may exist. Less than 500 miles northwest of the Nova Scotia fossil find is the enormous Manicouagan impact crater, its outermost ring--clearly visible in satellite photographs--measuring more than 90 miles in diameter. Given the margins of error in dating, the age of the crater (about 214 million years) makes it suspect in the 200 million-year-old extinction...
...works with the Alvarez team, is methodically examining rock samples from the Nova Scotia site, looking for evidence of shocked quartz--grains with their normal crystalline pattern distorted by the kind of shock wave the Manicouagan impact would have produced. If he finds the mineral clues below the fossil deposits, he says, the impact probably preceded and could have caused the extinction, thus strengthening the Alvarez hypothesis...
Whether or not Anders is successful, the fossil trove is already providing fresh insights about the evolution of life on earth. Says Shubin: "The find is like a Rosetta stone. This period was one of tremendous geological upheaval. The continents were beginning to split apart, and there was a turnover among the animals. The modern world was basically set during this time...