Dinosaurs ruled Earth for more than 150 million years before vanishing in what looks, geologically, like an instant. This film lays out the competing explanations paleontologists and geologists have argued over for decades, from the asteroid strike that carved the Chicxulub crater off the coast of Mexico to the massive volcanic eruptions that formed India's Deccan Traps around the same time. Interviews and field footage walk through the physical evidence embedded in rock layers worldwide, including the thin band of iridium-rich clay that marks the boundary between the age of dinosaurs and the age that followed. The film also considers how mammals, sidelined for most of the Mesozoic, managed to survive the same event that wiped out the dinosaurs and much of the rest of life on Earth. Rather than settling on a single culprit, it treats the extinction as a case built from clues in the rock itself, weighing impact, climate change, and volcanism against each other before showing what the evidence actually supports.