Why Did Scientists FIRST Hypothesize That a Meteorite Impact Caused

Why did scientists FIRST hypothesize that a meteorite impact caused the extinction at the K-Pg Boundary?

A) They found evidence of a giant tsunami on the Gulf coast.
B) They found evidence of an impact crater in Mexico.
C) They found evidence of wildfires in many regions throughout the globe.
D) They found evidence of Iridium enrichments in a clay layer that led them to believe that the Iridium was the remains of a meteorite impact.
E) They found evidence of acid rain in the rocks in the Southern Hemisphere.