This activity allows students to analyze the chemical data that led researchers to conclude that a layer of clay at the boundary between the Cretaceous and Paleogene rock layers (the K-Pg boundary) contained an extraordinary concentration of iridium. It supports concepts presented in the short film The Day the Mesozoic Died.

After watching the film, students will calculate the chemical signatures of two K-Pg (formerly referred to as K-T) boundary samples and compare them to those of a chondrite, a rock that originated from space, and a typical basalt, a rock that originated from Earth’s mantle. Students then evaluate elemental ratios to determine how well the evidence supports the conclusion that the iridium signal in K-Pg sediments was produced by an extraterrestrial impact.