Elevated levels of iridium are found in the geologic layer at the K-Pg boundary. Is this unusual?
A) Yes. Iridium is a common metal on Earth but rarely accumulates in a single layer.
B) No. Iridium is a rare element on Earth, but geological layers of iridium are not uncommon.
C) Yes. Iridium is a rare metal on Earth.
D) Yes. Composition differences between geological layers tend to equilibrate over time.

Question

Quizplus · Accepted Answer

Iridium is indeed a rare metal on Earth, and its elevated levels in the geologic layer at the K-Pg boundary are unusual because it is more commonly found in extraterrestrial objects, such as asteroids, than in the Earth's crust. This anomaly supports the theory that the K-Pg boundary event, which coincides with the mass extinction of the dinosaurs, was caused by an asteroid impact.

Elevated Levels of Iridium Are Found in the Geologic Layer