iridium anomaly

But he said the iridium anomaly was "a pretty minimal signal" that required more research.

"In many cases there is no iridium anomaly" in the global rocks of the period, he said.

But no such sharp iridium anomaly has been found in sediments coinciding with any of the other mass extinctions.

The type locality of this iridium anomaly is near Raton, New Mexico.

Further, an iridium anomaly - often an indicator of extraterrestrial impact - observed in Spain is far too small to denote a comet impact.

It is very important because the readily recognized iridium anomaly and primitive Danian planktonic foraminifers define the base of the Danian.

The base of the Danian is defined at the iridium anomaly which characterized the Cretaceous-Paleogene boundary (K-T boundary) in stratigraphic sections worldwide.

Others said the geology of the Permian extinction event lacked the iridium anomaly and other features that tended to support the impact explanation in the case of the Cretaceous extinction.

But no such iridium anomalies associated with the Permian extinction have been found, and there is wide agreement that the Permian "great dying," which wiped out nearly all ocean life and took a heavy toll on land animals, was caused by something different.

Verneshots have been proposed as a causal mechanism explaining the statistically unlikely contemporaneous occurrence of continental flood basalts, mass extinctions, and "impact signals" (such as planar deformation features, shocked quartz, and iridium anomalies) traditionally considered definitive evidence of hypervelocity impact events.

Asaro is best known as the nuclear chemist who discovered the iridium anomaly that led to the development of the asteroid impact theory to explain the mass extinctions, including the demise of the dinosaurs, that occurred at the end of the geological era known as the Cretaceous period in Earth's history.

An iridium anomaly has been discovered at the base of the cap carbonate formations, and has been used to suggest that the glacial episode lasted for at least 3 million years, but this does not necessarily imply a global extent to the glaciation; indeed, a similar anomaly could be explained by the impact of a large meteorite.