In the Discworld story the wizards learn that, once again, the history of Roundworld has changed, resulting in humans failing to leave Earth before the Extinction Level Event shown in the earlier books.
extinction | Cretaceous–Paleogene extinction event | Level 42 | High-level programming language | Impact event | Yanni Live! The Concert Event | Tunguska event | The Spirit Level: Why More Equal Societies Almost Always Do Better | prefecture-level city | Low-level programming language | Extinction | Saturday Night's Main Event | Local extinction | The Airborne Toxic Event | Split Level | Resident Evil: Extinction | Permian–Triassic extinction event | Low Level Owl | High Level Bridge | Fermi level | Birmingham Snow Hill to Wolverhampton Low Level Line | 2012 PDC European Tour Event 5 | Twelve Level Cap and Rank System | Tragedy (event) | ''The Main Event'' | The Beatnuts: Street Level | Scalp Level, Pennsylvania | Prefecture-level city | 'O' Level | Multi-level marketing |