An iridium-rich layer of clay,glass spherules,and shocked quartz grains strongly suggests that the K-T boundary extinctions were at least in part caused by
A) a long trend of global warming.
B) a long trend of global cooling.
C) worldwide explosive volcanism.
D) the impact of a bolide (meteoroid or comet).

Question

Quizplus · Accepted Answer

The presence of iridium-rich layer, clay, glass spherules, and shocked quartz grains suggest that the K-T boundary extinctions were caused by a bolide impact, most likely a meteoroid or comet. The high levels of iridium are consistent with extraterrestrial sources, as iridium is more abundant in meteorites than on Earth. The impact would have caused widespread fires, tsunamis, and a "nuclear winter" effect, leading to the extinction of the non-avian dinosaurs and many other species.

An Iridium-Rich Layer of Clay,glass Spherules,and Shocked Quartz Grains Strongly