Iridium in undersea crater confirms asteroid wiped out the dinosaurs – Physics World - physicsworld.com

An international team has measured an abundance of the rare element iridium in the crater and similarly high concentrations of the element are known to occur in sediments laid down at the time of the Cretaceous–Paleogene boundary (K–Pg) extinction event, which saw many species on Earth vanish.

The crater was discovered in the 1990s, but the idea that the K–Pg extinction was caused by an asteroid impact was proposed a decade earlier by a team that included the physics Nobel laureate Luis Alvarez.

Iridium is much more abundant in asteroids, leading Alvarez and colleagues to conclude that the vaporization of an asteroid released large amounts of iridium into the atmosphere, which then fell to the ground as dust as the dinosaurs disappeared.

However, the evidence linking the Chicxulub impact to the K–Pg extinction is not conclusive.

The iridium could have been put into the atmosphere by another asteroid impact or impacts; and some scientists have suggested that increased volcanic activity, rather than an asteroid, could have caused the extinction.