Deadly impact

A series of comet collisions with the Earth may have led to the extinction of many species

Published: Sunday 30 November 1997

studies reveal that a comet crashed into the Earth 370 million years ago, blasting a huge crater into the sea floor. Charles Sandberg, a geologist emeritus with the us Geological Survey, says this triggered 304 m waves that resulted in the extinction of many species. He feels that the crash may have been the first of the series of comet strikes that changed life on the Earth forever. It may also include the extinction of dinosaurs millions of years later.

The site of the collision is said to be 210 km northwest of Las Vegas in southern Nevada, whose area was covered by ocean. The blast created a crater on the sea floor that was 50-80 km in diameter. The impact of the blast was so intense that it ripped apart a reef on which continental shelf was present. Pieces of reef as large as 0.8 km wide scattered in southern Nevada in 190 km of diameter.

Sandberg conducted studies for several years in the area and found blocks of reef, turned into a kind of rock called Alamo Breccia.

His other two colleagues, John Warme at the Colorado School of Mines and Jared Morrow at the University of Colorado, usa , say that the mass destruction stretching nearly 96 km farther than earlier thought. The crash took place three million years before one of the five greatest extinctions of life in the Earth's history. At that time, most species lived in the ocean.

Researchers have also found other evidence to substantiate their findings. They have located crystals of shocked quartz that are sand grains shattered by the force of the impact, a rock layer rich in iridium that is a rare element on the Earth but common in asteroids and comets.

In recent years, they have discovered a crater similar rocks in other countries, suggesting that the Devonian extinction was triggered by a series of crashes.

Sandberg does not rule out the possibility of other comet crash into the Earth in future. He say that scientists will have to investigate for such possibilities.

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