Silurian Earth
The Silurian Earth was an alternate timeline, created by the Monk, of the Earth in the late 20th century. In this time the planet was ruled by the Silurians and dinosaurs had been reintroduced into its ecosystem.
This alternate time was created when the Doctor's first encounter with the Silurians was changed so that, in his incarnation at the time, he was killed and UNIT's plans to bomb the Silurian settlement were stopped and the Silurians took control of Earth.
A later incarnation fell from the Time Vortex and landed in the Silurian Earth in 1993. It was through his doing that the Silurian Earth was destroyed, since if it had been allowed to continue to exist, the real universe would have ended ten billion years earlier. (PROSE: Blood Heat)