While the probability of our planet stopping to spin seems to be almost zero, a slight possibility does exist and paves the way for us to develop the probable theories around the consequences of such a case to occur. The fact that earth has seen a constant day-time consisting of 24 hours is only in between the brackets of human knowledge. What was the speed of earth several millennia ago, and what will it be after a plentiful of millennia down the line are questions not known. Scientists have been drawing quite a few plausible theories to predict what lies ahead for the fate of our planet.
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Currently, what is known to us, is that the planet is slowing down at a rate of 1.7 milliseconds per century. It is believed that this is due to the moon's tidal effect on the planet. If the earth stops rotating all of a sudden, then the atmosphere present around the planet would still be intact at the current earth's speed of 1100 miles per hour at the equator. With the earth at a standstill and the atmosphere in rotation, it would result in all the masses on earth to get uprooted, circle around the planet, and land at another spot across the planet.
For example, a young man is driving on a highway for leisure on a bright and sunny day. He passes a cluster of restaurants a little distant from him. If the earth were to suddenly cease its spin then, this young man would see him, his car, the road, the vegetation around him, the restaurants, and everything and everyone in them flying into the air. As of now, the fastest wind ever recorded is 253 miles per hour, but the wind is almost four times as strong, hence the scenario would be just as deadly.
In addition to this, since the earth bulges at the poles due to centrifugal force experienced by the planet, all the ocean's water would flow towards them leaving a massive single continent at the equator. Due to the overflowing water several parts of North America, Europe, Asia, Australia, South America, and most of the arctic regions would be submerged. This would leave the equatorial and tropical regions to experience drought and the existing life (if any left) would be deprived of food and water due to lack of vegetation.
The natural transition between seasons would also be inhibited due to the year-long day. The final and most fatal consequence would be the loss of the magnetic field of the earth. The earth's magnetic field plays an important role in blocking the sun's deadly cosmic rays, in the absence of it, our atmosphere would pave way for these high-frequency rays to enter the earth's atmosphere, and destroy any life that is left on the planet.
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On the other hand, if the rotation of the earth is gradually decreased over billions of years, to around one rotation for 365 days resulting in a condition called, 'sun-synchronous,' then the scenario would be quite different. The chances of occurrence of this possibility are pretty high in comparison to the earlier. In this case, a portion of the planet would have perennial sunlight while another would be in constant darkness. This is not exactly the termination of the rotation of the planet, but it is quite close.
In the impossible scenario, six months in sunlight and six months in the night what happens when the earth stops rotating altogether. The winds would alter and the circulation would be in between the poles rather than the currently existing east to west. Adding to this effect, if the earth stops rotating altogether the temperatures on earth would also alter and the equatorial regions would be much hotter and the regions near the poles would be much colder due to slant rays of the sun they are exposed to.
1. What Would Happen If The Earth Stops Rotating And Then Starts Again?
If the earth stops rotating, it would result in extreme effects such as landmasses being uprooted due to deadly winds, very high temperatures in one half of the planet and very low temperatures in the other half, superstorms and cyclones due to exchange of winds between the cold and bright sides of the planet, drifting of water bodies to the polar regions resulting in the formation of a huge single continent in the equatorial region of the earth, and many more devastating effects that would destroy all the life on earth. If the earth starts rotating again, over several millennia the planet would see life again probably the earlier conditions would be restored.
2. The Earth May Stop Spinning. Is It Possible?
Scientists have predicted that the speed of earth may gradually reduce and come to a standstill in billions of years from now, but the probability of other events to occur before this is higher. The possibilities are that the sun may consume the planet and eventually die while expanding or a large asteroid may collide with our planet and destroy it or distort its orbital position in the solar system before it stops to spin. If the sun eats up earth and a few other planets orbiting it, it may explode into a supernova and destroy everything in the field of its explosion.