The timeline below appeared in Thrilling Wonder Stories, Winter 1955, pp. 62-63. The sidebar describing it includes the following:

“Asimov says: ‘It’s not the beautiful job that Heinlein did, but was actually made up ad hoc. My cross-references in the novels are thrown in as they occur to me and did not come from a systematized history.

“‘The fact that I only reach about 48,000 A.D. may be surprising–it surprised me! I had never once thought of the actual dates of my stories and now that I come to write them down, I find that I haven’t been so far flung as I thought. If some reader checks my stories carefully and finds that my dating is internally inconsistent, I can only say I’m not surprised.”

For the record, I’m not endorsing this timeline. I merely provide it for those interested in the development of Asimov’s perception of his fictional worlds. Meanwhile, it appears I should start packing to move to the Moon, or maybe even Mars…


A Page from Isaac Asimov’s Notebook
 
A. Exploration of the Solar System
Year Story Events
1975 Trends First man-carrying flight to the moon, against social resistance
1985 The Singing Bell Settlement of the moon proceeds; mining operations set up
2000 The Martian Way Mars settled. Much of humanity still rebels against settlement of other planets. This is finally overcome.
2020 Ring Around the Sun Venus settled. Mail service between planets established.
2050 Marooned Off Vesta Passage across asteroid belt no longer a matter of exploration. Commercial flights across the belt begin.
2100 Heredity
The Callistan Menace
Christmas on Ganymede
The moons of Jupiter are settled. Human eyes turn toward intergalactic space. The hyperspatial drive is discovered about 5000 A.D.
B. Exploration of the Galaxy
5500 The Recipe Flights to other stars become feasible in small space cruisers. Very little of the Galaxy explored.
6500 Green Patches [sic] Organized space exploitation begins. Mankind begins spreading outward.
8500 Sucker Bait Population has increased to the point where the inner regions of the Galaxy are overcrowded. Government-sponsored emigration to the outer reaches are begun. Most of the Galaxy now mapped and well-known. The old political structure is now incapable of handling the vast number of worlds. Earth’s last atomic wars render its crust largely radioactive about 10,000 A.D. and that is the last straw. The Galaxy breaks up into numerous political organizations.
C. Galactic Empire
30000 The Stars, Like Dust (Tyrann) The star-regions begin to agglomerate into larger groupings. The empire of Tyrann grows and declines. Trantor grows less spectacularly, but more solidly.
34500 The Currents of Space Trantor has grown until half the Galaxy is under its sway. The Squires of Sark, with their control of the kyrt-rich Florina, are the last independent group to seriously contest Trantor’s hegemony. Trantor becomes the Galactic Empire officially, about 35,000. Earth is all but forgotten.
36500 Pebble in the Sky
Blind Alley
Galactic Empire is at its height. Earth completely forgotten as origin of humanity. Slowly the Empire grows static and decadent. Hari Seldon is born about 47,000.
47000
to
47500
The Encyclopedists
The Mayors
The Merchant Princes
The General
The Search by the Mule
The Search by the Foundation
The Galactic Empire settles into final decay. Its last battle with the rising Foundation dates at 47,200. The Mule rises and falls somewhere around 43,000. The Second Galactic Empire is established at 48,000.

Note: A similar historical pattern can be constructed for those stories which do include the development of positronic robots, beginning with Strange Playfellow and ending with The Caves of Steel. There are also many stories that fit into neither pattern.