Asimov’s 1950 Pebble in the Sky is either the first (by publication date) or the third (by internal chronology) of three standalone novels (The Stars, Like Dust, The Currents of Space, and Pebble in the Sky) set some millennia prior to the beginning of the Foundation trilogy. The three novels form a loose trilogy that has been dubbed the Empire novels or sometimes the Galactic Empirenovels.
The Stars, Like Dustis set long before Trantor began its rise to power; The Currents of Space is set during its rise. Pebble in the Sky is set at the height of the Galactic Empire’s power.
The book opens with an Eisenhower-era tailor, Joseph Schwartz, who finds himself transported onto a desolate alien world. He later learns that he is still on Earth, an Earth of the far future. The plant has been scoured by nuclear war. Even though this happened some time ago, Earth is still radioactive in places and is largely sterile.