Frank Kyte, a geochemist from University of California at Los Angeles (UCLA), presents his analysis of the fossil meteorite in the November 19 issue of the journal Nature.

Some scientists believe that this particular worldwide extinction, which ended the Cretaceous period 65 million years ago, was caused by the destructive impact of a comet or asteroid. Kyte found the fossil meteorite while studying the sediment boundary layer between the Cretaceous and Tertiary eras.

Hidden in mud and buried beneath the Pacific Ocean for 65 million years, the fossil is no longer composed of all of its original minerals, yet has retained its original shape and texture.

"The fossil is a record of the original rock," said Richard Lane, program manager in NSF's earth sciences division, which funds Kyte's research, "much like fossilized traces of dinosaur skin, or, more appropriately, like casts made from the victims of Mt. Vesuvius at Pompeii whose imprints were preserved in the volcanic ash."

According to Kyte, it is likely that the fossil depicts the remains of a colossal asteroid, some six miles wide, which collided with the earth near Mexico's Yucatan peninsula. His findings suggest that the original meteorite had a rocky composition that corresponds with the makeup of asteroids, as opposed to the porous materials that would more likely be found in a comet.

Although the fossil itself is only a tenth of an inch long, Kyte was able to deduce its origins using instruments from UCLA's electron microprobe and neutron activation laboratories. These instruments, which can identify the chemical components of a given substance, found the fossil to be high in iridium, an element found in relative abundance in asteroid meteorites.

In our solar system, asteroids are found orbiting the sun in a belt between Mars and Jupiter. This rocky belt of space debris is thought to be a leftover from the time when the planets first formed.

Kyte notes that this particular asteroid moved out of the belt towards Earth at about 40,000 miles per hour. The resulting impact is thought to have had devastating consequences for the world's climate and could have led to the extinction of the dinosaurs and many other forms of life.

"Studies like Kyte's show that celestial impacts have had a profound effect on the history of the earth," said Lane. "One begins to think that such catastrophic events played at least as important a role in shaping the earth as did more gradual processes."

Note: If no author is given, the source is cited instead.

• Asteroids, Comets and Meteors
• Solar System

• Near-Earth Object Impacts
• Earth Science

• Paleontology
• Dinosaurs

• Trace fossil
• Cretaceous-Tertiary extinction event
• Extinction event
• Meteorite
• Impact event
• Chicxulub Crater