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Scientists find evidence of Argentine asteroid

graphic

Collision 3.3 million years ago changed climate

December 11, 1998
Web posted at: 8:17 p.m. EST (0117 GMT)

WASHINGTON (Reuters) -- Scientists said Thursday they have evidence a killer asteroid smashed to Earth in southeastern Argentina 3.3 million years ago, possibly causing climate changes that wiped out 36 species of animals.

Glassy fragments found in the soil in this part of Argentina's vast pampas suggest intense heating that could only have come from an asteroid impact. The glass resembles similar materials found in known craters.

"It's clearly an asteroid that hit," said Peter Schultz, a planetary geologist at Brown University who led the study. "The Earth does get hit just as the moon gets hit."

The study, published in the journal Science, adds evidence to the theory that asteroids have struck the Earth throughout history, sometimes causing extreme changes in the climate.

While this asteroid did not devastate the globe like the one scientists think killed off the dinosaurs 65 million years ago, it was deadly locally, probably bringing on cooler temperatures and distinct seasons.

Giant armadillos, ground sloths and a large-beaked carnivorous bird were unable to adapt to the colder environment and soon died out.

The big asteroid 65 million years ago, known as K-T to geologists, is believed to have kicked up dust that sent the planet into many years of year-round winter.

"K-T was a killer -- this was a wound," said Schultz. The K-T asteroid would have been 10 to 15 miles across, while this smaller one measured only about 1 mile in diameter, he said.

The greenish-colored glassy material in the area, called escoria, was the main clue that an asteroid hit, Schultz said. Scientists had been aware of the materials for a long time but thought either a fire or volcanic eruption had left the fragments in the Earth.

But in analyzing the deposits found across a broad area, the researchers discovered unusually high levels of magnesium oxide, iridium and chromium, and they also found that the mineral zircon had been broken down by the heat. This was something neither a volcano nor campfire could have done.

"Without the escorias, we would not have any idea," Schultz said in a telephone interview. "You don't get this naturally, and this is one of the key signatures of an impact."

Soon after the asteroid landed, local air and water cooled, and some animal species disappeared.

"These coincidences suggest that the impact may have directly induced regional faunal extinctions or triggered broad environmental changes leading to ecosystem collapse in Argentina," Schultz's team wrote in their report.

"We were surprised to find that the appearance of the glasses and the turnover of the fauna coincided with a temperature drop," Schultz added in a statement.

The impact from the speeding asteroid, 25 times faster than a rifle bullet, could have roiled the ground and sent dust and water particles up into the atmosphere, cooling it, Schultz said.

"When you toss materials into the Earth's atmosphere, it can cause change," he said.

The international team of scientists has not located the crater where the asteroid landed. This could be because the coast has eroded inland.

But further study of the asteroid impact is helpful in understanding other natural events, like El Nino and volcanic eruptions, that can also cause climate change and sudden stress on the Earth, Schultz said.

"This is one of those events that is another type of tweak in our Earth's system," he said.

Copyright 1998 Reuters Limited. All rights reserved.

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