Four and a half billion years ago, a Mars-sized planet called Thea collided with the young Earth, and the debris ring left behind became the Moon. This first episode of the five-part Catastrophe series has host Tony Robinson tracing that impact and its aftermath with planetary scientists, archaeologists, and paleontologists. Planetary scientist William K. Hartmann lays out the collision theory, and astrophysicist Robin Canup backs it with computer models showing how a single impact could produce a body like the Moon. Paleontologist Judith Nagel-Myers examines fossilized corals found near Ithaca, New York, as evidence that the early Moon orbited roughly ten times closer to Earth than it does now, generating tides powerful enough to spread minerals and nutrients across the planet's surface. The film also covers the icy comet bombardment that filled Earth's first oceans and the rise of cyanobacteria and photosynthesis that followed. The episode's argument is that the Moon's formation, born from catastrophe, set the specific conditions that made life possible.