An iridium-rich layer of clay,glass spherules,and shocked quartz grains strongly suggest 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 an iridium-rich layer along with other evidence such as glass spherules and shocked quartz grains strongly suggest that the K-T boundary extinctions were caused by the impact of a bolide (meteoroid or comet), rather than global warming or cooling or volcanic activity.

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