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Circa 10,000,000, Earth was devastated by solar flares. A vast Ark was launched for Refusis II. The Doctor's TARDIS landed on the Ark. Dodo Chaplet's cold caused a plague, which the First Doctor was able to cure. (TV: The Ark)

By some accounts, this was when the posthuman era began. (PROSE: The Book of the War, Of the City of the Saved...)