Ninety-nine percent of species that have ever existed are extinct, and this film sets out to explain why by walking through the Big Five mass extinctions. It opens with the Ordovician die-off around 440 million years ago, when researchers now suspect a gamma-ray burst from a collapsing star stripped away the ozone layer and let solar radiation scour the oceans. From there the film moves through the Permian-Triassic event, nicknamed the Great Dying, driven by volcanic eruptions in Siberia that poisoned the atmosphere for millennia, and ends with the Chicxulub asteroid that ended the age of dinosaurs. Paleontologists and geologists lay out the physical evidence for each event, from rock strata to iridium layers, and the narration keeps returning to a single question: what pattern connects these five catastrophes, and does it tell us anything about the next one. Graphics and animated reconstructions fill in what the fossil record cannot show directly.