The 1-cm-thick clay layer that marks the Cretaceous/Tertiary (K/T)boundary has a high percentage of the element ________ in the clay layer,an enrichment about 300 times greater than the normal abundance.
A)iridium
B)silicon
C)iron
D)oxygen
E)zircon

Question

Quizplus · Accepted Answer

The element with a high percentage in the 1-cm-thick clay layer that marks the Cretaceous/Tertiary (K/T) boundary is iridium. This enrichment is about 300 times greater than the normal abundance, which is a clear indication of an extraterrestrial origin, possibly from a meteorite impact.

The 1-Cm-Thick Clay Layer That Marks the Cretaceous/Tertiary (K/T)boundary Has