Academic journal article The Science Teacher

Researchers Say a Comet-Not an Asteroid-Killed the Dinosaurs

Academic journal article The Science Teacher

Researchers Say a Comet-Not an Asteroid-Killed the Dinosaurs

Article excerpt

About 66 million years ago, something killed off almost all the dinosaurs and some 70% of all other species living on Earth. Only those dinosaurs related to modern birds appear to have survived. Most scientists agree that the culprit was extraterrestrial with the prevailing opinion that the party crasher was an asteroid.

Not so, say Dartmouth Earth science professors Jason Moore and Mukul Sharma. They assert that a high-velocity comet caused the extinction.

The asteroid impact theory of extinction began with discoveries by the late physicist Luis Alvarez and his son, Walter. In 1980 they identified extremely high concentrations of the element iridium in a layer of rock known as the K-Pg (formerly called K-T) boundary. The layer marks the end of the Cretaceous period (abbreviated "K"), the epoch of the dinosaurs, and the beginning of the Paleogene period, with its notable absence of the large lizards.

While iridium is rare in the Earth's crust, it is a common trace element in rocky space debris such as asteroids. Based on the elevated levels of iridium found worldwide in the boundary layer, the Alvarezes suggested that this signaled a major asteroid strike around the time of the K-Pg boundary. Debate surrounded their theory until 2010, when a panel of 41 scientists published a report confirming it.

The scientific community today looks to the deeply buried and partially submerged, 110-mile-wide Chicxulub crater in Mexico's Yucatan as the place where the death-dealing asteroid hit. The 66-million-year age of Chicxulub, discovered in 1990, coincides with the K-Pg boundary, leading to the conclusion that what caused the crater also wiped out the dinosaurs.

Moore and Sharma agree that Chicxulub was the impact zone but dispute the characterization of the object from space as an asteroid. In a paper presented to the 44th Lunar and Planetary Conference in March, they described their controversial findings.

Moore notes that in the past geochemists toiled apart from their geophysicist colleagues. "There hadn't been a concerted synthesis of all the data from these two camps," Moore said. …

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