Ice Age

Several Ice Ages mark the history of the planet Earth.

Distant past
One Ice Age occurred in the time of early humans (DW: An Unearthly Child) and Neanderthals (DW: Ghost Light) During this time, an Ice Warrior craft from Mars crashed and buried itself. (DW: The Ice Warriors) One Neanderthal was preserved by Light. (DW: Ghost Light) The Dæmons visited Earth, and according to the Third Doctor, inspired cave paintings of powerful supernatural beings, They favored humans over Neanderthals, causing the latter to die out. (DW: The Dæmons)

In Birmingham during the Ice Age, the Doctor and Amy Pond saved a group of Neanderthals who were being experimented upon by aliens. (DWAM: Snow Globe)

51st century Ice Age
Earth suffered another ice age circa the year 5000, a time period visited by the Doctor during an unknown incarnation (DW: The Talons of Weng-Chiang) and, later in his life, during his eighth incarnation (EDA: Emotional Chemistry).

Other information
The Second Doctor met the de-thawed Ice Warriors in a future time period. We do not know for certain if this occurred circa 5000 or earlier or later. (DW: The Ice Warriors)

Behind the scenes

 * Publicity material for The Ice Warriors set that story in the year 3000.