If the planet simply came to a grinding halt billions would be dead in seconds.
The first thing that would happen is millions of people would smash into walls and buildings at the almost twice the speed of sound and be turned into mush.
The earth at the equator rotates at about 1000mph (1,600 km/h) eastwards – though it slows towards the poles.
If the earth suddenly stopped spinning everything not tied down – including people – would keep on moving eastwards at up to 1000mph relative to the ground. If the planet’s revolution actually reversed it would be even worse meaning people would hit static objects at almost 2,000mph.
Anyone who survived that horror would then face 1000 mph super-hurricane force winds – far stronger than anything ever experienced – which would likely reduce every human structure from New York skyscrapers to Egypt’s pyramids to ruins.
And again billions would be killed.
The earth’s rotation and friction with the ground mitigates much of the force of the planet’s winds – but if the globe stopped spinning an onslaught would ensue.
Those lucky enough to find themselves in a nuclear bunker, or an underground station might survive – but they would then face the twin agonies of radiation sickness and a glut of cancers.
Earth’s magnetic field – which protects us from massive doses of radiation from outer space – would fail.
Penn State astrophysicist Kevin Luhman, who has researched the proposition, said: “The Earth is surrounded by a magnetic field, and that magnetic field is generated by the core of the Earth in its spin.
“No spinning liquid iron core, no magnetic field. We need the magnetic field of the Earth to shield the Earth from the sun. If we didn’t have the magnetic field, life on Earth would be in really bad shape.”
If the planet started spinning in the opposite direction the effects would be arguably weirder.
First the Earth’s magnetic poles would reverse and of course the Sun would rise in the West – probably killing off any migratory animal or bird who navigate using the field.
The earth’s crust would also likely break up – and fold mountains like the Himalayas would start shrinking as they slowly unfolded.
The word’s Coriolis effect – which governs weather patterns and oceanic currents – and causes winds at the equator to blow toward the west (opposite the direction of the earth’s spin at the equator) would be reversed too.
BBC meteorogist Peter Gibbs has worked through this thought experiment.