Sixty-five million years ago, something wiped out roughly 70 percent of life on Earth, including the dinosaurs, and this episode traces the evidence that points to an asteroid. The trail starts with paleontologist Jan Smit, who found unusually high concentrations of iridium, an element rare on Earth but common in meteorites, in rock layers along the cliffs of northern Spain three decades before this film was made. That discovery sent researchers hunting for an impact site, eventually leading to the Yucatan Peninsula and comparative fieldwork in the mountains of Colorado. Planetary scientist Dan Durda and other geologists and paleontologists lay out what the rock record actually shows. Hyper-realistic animation reconstructs the impact itself: firestorms racing across continents, tsunamis reshaping coastlines, and a climate collapse that lasted centuries afterward. Narrator Tony Robinson frames the extinction as the accident that cleared space for mammals, and eventually humans, to take over. The episode is part of a five-part series on Earth's catastrophic history, and this installment stays focused on the asteroid case from first clue to aftermath.