 |
|
 |
 advertisement
| |
|
|
|
|
|
Mass Extinction & Rise of Dinosaurs Tied to Cosmic Collision
By Robert Roy Britt
Senior Science Writer
posted: 02:00 pm ET
22 February 2001
|
Calling card: ET Buckyballs
The key to the new finding lay inside odd molecules known as Buckyballs, which scientists describe as looking somewhat like tiny soccer balls.
Buckyballs are complex carbon molecules more scientifically known as fullerenes. They are named after Buckminster Fuller, who invented the geodesic dome (which also looks like a soccer ball). Buckyballs have a unique characteristic: They can trap helium and argon gas inside their cage-like structures.
The research team studied Buckyballs found in exposed soil layers known to be 251 million years old, from sites in China and Japan. Inside these fullerenes, the scientists found gases with a particular structure that could not have formed in our solar system. So these molecules are not only from beyond Earth, but from beyond our solar system, having formed in some distant primordial environment unlike the one created by our Sun. They would have then been incorporated into a comet when our solar system formed.
| Death of the Dinos | | Beginning in the 1980s, researchers found evidence that a giant impact caused a mass species die-off 65 million years ago, known as the Cretaceous-Tertiary extinction, that led to the demise of most dinosaurs. In 65 million-year-old soil around the world, researchers found up to 100 times the amount of iridium -- a signature of asteroids and comets -- than what occurs normally. | 
Later, a 120-mile- (200-kilometer-) wide crater was found mostly buried under eons of sediment in Mexico"s Yucatan Peninsula, near the village of Chicxulub. Aerial photographs reveal only a hint of the crater"s rim. Learn more. |
Scientists say the object that slammed into Earth 251 million years ago, which may have been a comet, likely had a different composition than the presumed asteroid that hit the Yucatan Peninsula 65 million years ago, and hence left behind only small quantities of iridium. Comets travel at greater speeds, and if it were a comet, it may have been on the small end of the size estimate in the report. A small, fast-moving comet could generate the same destruction as a larger, slower asteroid.
Quick end
Researchers suspect that the Permian-Triassic Boundary event, as the 251 million-year-old extinction is known, happened very quickly. Previous fossil evidence has shown a sharp reduction in the number of certain species at the boundary between the Permian and Triassic periods in history. The entire die-off is thought to have taken place in less than 100,000 years.
"That's a microsecond in geologic time," Becker said. She and her colleagues say the newly proposed scenario, in which species would have toppled one after the other going up the food chain, fits that short time frame.
Becker and her colleagues plan to apply the new technique to other known mass extinctions, including one in the Devonian period, 364 million years ago, and another at the end of the Jurassic period roughly 200 million years ago. This latter event coincided with the breakup of Pangaea and the birth of the Atlantic Ocean.
Death and life
Scientists say the new discovery, funded by NASA and the National Science Foundation, is further evidence that comets and asteroids are both killers and master chefs in the grand recipe of life. Comets may have delivered the water that transformed a dry early Earth into a watery orb, and comets and asteroids both have been found to pack some of the molecules needed to seed life.
The field of astrobiology has burgeoned in recent years as researchers scramble to confirm whether life on Earth originally came from space.
Meanwhile, the findings should not change our view of the potential fragility of our own species, said Theodore Bunch, a geologist at NASA's Ames Research Center in California who also worked on the study. Estimates of potentially devastating impacts have already been worked out based on other factors, Bunch said, including impact evidence on the Moon and Mars, which preserve craters better than Earth.
Asteroids or comets big enough to cause global destruction are estimated to come around every 100 million years or so. Smaller space rocks -- still big enough to destroy a city or generate a deadly tsunami in the ocean -- are thought to hit the planet every 1,000 to 10,000 years.
The most recent scare was the Tunguska event in 1908, which flattened some 1,200 square miles (3,108 square kilometers) of Siberian forest. The suspected asteroid involved was never found -- it didn't even reach the ground. The object, thought to be about 60 yards (55 meters) wide as it sped into Earth's atmosphere, exploded 3 or 4 miles (5 kilometers) from the surface, experts now believe.
The explosion was like several tons of TNT. It broke windows and knocked people to the ground 37 miles (60 kilometers) away in the sparsely populated area, says William K. Hartmann of the Planetary Science Institute in Tucson, Arizona. A fiery cloud was seen up to a distance of 300 miles (500 kilometers), where witnesses reported hearing "deafening bangs." The explosion sent a rush of hot wind that felled and burned the trees.
Chyba, of the SETI Institute, said there's no need to panic, and no need right now to spend money to defend Earth against any potential species-ending impact.
"Even if one of these objects is likely to hit Earth [anytime soon], and that's very unlikely, we would almost certainly have decades, if not centuries, to go before that impact would happen," Chyba said. "So we'd have a long time to think about what to do about it."
Meanwhile, researchers are working to catalogue asteroids and comets that could pose a threat. Of the 1,000 or so expected to exist, each more than a kilometer wide, about 400 have been found. Chyba said 90 percent of them should be detected by the year 2015.
Click here for more news and information about asteroids and astrobiology.
| | | |
