Question

In 1980, a group of scientists from The University of California at Berkeley found an unusually high concentration of iridium in a rock layer thought to be 65 million years old. Iridium is rare on Earth, but is sometimes found in meteorites. Similar iridium deposits in similarly aged rock were found all over the world. The evidence above supports which hypothesis?
A) Glacial movement ceased 65 million years ago.
B) An asteroid impact started the ice age 65 million years ago.
C) A giant volcanic eruption caused a mass extinction 65 million years ago. D) The Earth was hit by an one or more objects from space 65 million years ago.

Answer 1

D) The Earth was hit by a one or more objects from space 65 million years ago. The iridium layer shows an extraterrestrial cause for the extinction at the Cretaceous Tertiary boundary, discovered by the Alvarez family. The first discovery of this layer was in the Bavarian alps, in Lattengebirge. The Alverez family proposed that the extinction of the dinosaurs was due to a large meteor hitting the Earth at the end of the Cretaceous period, marking the KT boundary with this clay layer which has a high content of iridium. Iridium is not common on Earth, but is common in meteors.