Some scientists theorize a giant asteroid impact may be the reason dinosaurs became extinct RELATED VIDEO CNN's Rick Lockridge reports on the find Windows Media 28K 56K

LOS ANGELES (CNN) -- For years, the scientific community has theorized that a giant cosmic "impactor" slammed the Earth 65 million years ago, wiping out the dinosaurs and much of the rest of life on the planet. Now, one researcher claims he has found a piece of the rock.

UCLA scientist Frank Kyte has analyzed a small piece of a fossilized meteorite excavated from the North Pacific Ocean. He said it must have broken off from the asteroid when it shattered on impact, sending it thousands of miles from the asteroid's supposed crash site in Central America.

Kyte considers it "highly" likely that his sample is from the asteroid responsible for killing the dinosaurs. If he's correct, it would be the first piece ever found that was big enough to analyze.

The small fossilized meteorite found in the North Pacific Ocean

According to the theory, an asteroid or comet 6 miles in diameter struck the Earth near Mexico's Yucatan Peninsula, on what Kyte calls Earth's "worst day in the last billion years." The collision threw up a huge debris cloud that caused widespread environmental damage and the extinction of almost all living things.

Kyte said his analysis, published in this week's edition of the British journal Nature, points to an asteroid, not a comet. The rock was found in a sediment layer known as the Cretaceous/Tertiary boundary, where scientists have previously found unusually large amounts of the element iridium, which is rare on Earth.

Kyte says the tiny iridium-and-iron chip in his sample could only have come from an asteroid. And he said that should end the debate over what killed the dinosaurs.