65 million years ago: The dinosaur extinction does not happen
Earth is spared collision with asteroid
Sixty-five million years ago, the dinosaurs still ruled land and sea, as they had for more than 100 million years. Then a comet or asteroid struck our planet, wiping out 60 to 80 per cent of all species. Earth was unlucky to have been hit so late in its evolution. With no impact, the climate would have continued to evolve, species to rise and fall. Intelligence could have arisen, among birds or mammals, so they relied on brains rather than brute strength. One day, something similar to humans might have faced something like the dinosaurs. But we were hit and, although dinosaurs succumbed, some rat-like mammals dug themselves into the ash and survived.
476: Rome never falls
A Roman industrial revolution drives a unifying empire
Did Rome have to fall? After military defeats, the emperors tried to establish "natural boundaries", such as the Rhine and Hadrian's Wall, thus halting the empire's growth and economic development. They were technologically advanced and came close to the invention of steam engines. But such things were treated only as toys, and the chance of a Roman industrial revolution was lost.
If Rome had survived it might have fought off Islam where Byzantium failed, and handled the Mongols better than their medieval successors. In the Americas they wouldn't have practiced genocide as the British did, but assimilated, in the Roman way. In Europe, united in empire, there would be no feudalism, no chivalry - no parliaments - and no Great Britain.
1945: Germany wins World War II
With their V2 rocket technology the Nazis are the first to conquer space
After Allied bombing, there isn't much left to see of Peenemnde, on Germany's Baltic coast. But this was the world's first rocket station. Here Wernher von Braun developed the V2 ballistic missile, which was the ancestor of both the US and Russian space programmes. And this place is the hinge of one of the most tantalising what-if s of all. Hitler might have won the Second World War if Britain had settled for a truce after the fall of France in 1940, if he hadn't made the catastrophic decision to invade Russia or if the Nazis had developed an atomic bomb before America. This could have seen Peenemnde become a spaceport. By 1945, von Braun's plans were well developed -especially the A10 (in the Germans' jargon, the V2 was the A4). With a large first-stage booster and a winged V-2 mounted on top, it was comparable to the Atlas rocket that launched John Glenn into orbit in 1962. Von Braun led the Apollo programme which reached the Moon in 1969. With Nazi money the Germans might have got there earlier. They could have set up a lunar missile base for attacks against America, a plan floated by the US during the Cold War.
4.5 bilion years ago:The Moon neverformed
Life on Earth is very different' that is, if there's any life at all
The young Earth was wrapped in a blanket of cloud. Through a hierarchy of impacts, cloud particles gathered into whizzing asteroid-like bodies. The collisions were spectacular' Earth's final visitor was the size of Mars. Where the planets touched, a ring of fire formed, shattering the surface of both. Liquid rock gushed into space, and a glowing ring coalesced inorbit. Our Moon was born. Without it, and the gradual slowing of the tides, Earth's day would be about eight hours. The air would be rich in oxygen but laden with carbon dioxide. Given the fast rotation, there would be violent winds and no trees. Animals would need strength, armour, low profiles and would have fast metabolisms. The Moon stabilised Earth's rotation. Moonless Earth would have dramatic climate shifts- droughts, floods and ice ages.
1441: Chinese explorers discover America
The New World is found, 50 years …