A 200-million-ton rock carries more destructive energy than every nuclear weapon on Earth combined, and this film sets out to prove it. The investigation opens at Arizona's Meteor Crater, a 50,000-year-old scar nearly a mile wide, before moving to the buried Manson impact site in Iowa, a crater so old it left no visible trace on the landscape but still shows up in the geology once you know where to dig. Geologists and impact researchers walk through how a strike from a mile-wide asteroid would release energy equivalent to 100 million megatons of TNT, and how Earth's position in the solar system puts it in what the film calls a celestial shooting range. Along the way it covers how these craters are identified, dated, and distinguished from ordinary geological formations, and what the size and frequency of past impacts imply about the odds of another one. The pairing of a visible crater and an invisible one makes the scale of the threat concrete rather than abstract.