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Rotation is ubiquitous in the cosmos. Planets rotate, as do stars and galaxies. This comes about simply from conservation of angular momentum. What if Earth stops rotation ? How does it effect on living beings?

I am not talking about Earth's revolution.

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    $\begingroup$ Does it stop immediately, or does it slow down gradually and then stop? Does it stop rotating relative to the sun, or relative to something else? VTC until this question is a bit more clear. $\endgroup$ – jdunlop Feb 1 at 8:02
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    $\begingroup$ Maybe after a period of stillness Earth will probably start rotating again, thanks to our moon pulling on the ocean unless you want everything to stop in-situ then can someone turn on the bat signal in the day otherwise it won't be my turn to save wb ;D $\endgroup$ – user6760 Feb 1 at 8:14
  • $\begingroup$ I think we really need to know how it stopped rotating, what caused it, and why. The energy that it would take would have significant effect on a lot of things besides just the Earth's rotation. Was this energy all concentrated in one spot (like a meteor strike) or was it distributed over the entire Earth (like some form of electromagnetic brake)? $\endgroup$ – Justin Thyme the Second Feb 1 at 15:39
  • $\begingroup$ I assume you're not talking about the XKCD link. How is your question different? $\endgroup$ – Mathaddict Feb 1 at 16:24
  • $\begingroup$ @user6760 The moon doesn't just pull on the Earth's oceans, it pulls on the Earth itself. It's just that the oceans are made of water, so they move more obviously. $\endgroup$ – NomadMaker Feb 1 at 17:26
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If it happened suddenly, there would be no life left.

Quoting Dr. Sten Odenwald:

If the Earth stopped spinning suddenly, the atmosphere would still be in motion with the Earth's original 1100 mile per hour rotation speed at the equator. All of the land masses would be scoured clean of anything not attached to bedrock. This means rocks, topsoil, trees, buildings, your pet dog, and so on, would be swept away into the atmosphere.

And again:

If the Earth stopped rotating, it's magnetic field would no longer be regenerated and it would decay away to some low, residual value due to the very small component which is 'fossilized' in its iron-rich rocks. [...] This is a significant biohazard.

There's also to consider the change in temperature, having 6 months of day and 6 months of night. On Earth we currently see that only in the polar regions. Life still exists in those areas, especially marine life.

One important note: their climate depends not only on the 6 months light cycle, but also on their angle relative to the sunlight. That's to say that not all Earth would look like that.

Quoting Dr Karl Kruszelnicki:

Life could continue in a narrow twilight zone between the hot and cold halves. But this twilight zone would slowly creep around the planet over the period of a year, as the Earth did its annual orbit around the Sun.

And again:

The liquid water in the oceans is far more mobile and responsive to forces. So the Earth's spin has pushed up this liquid water to an 'abnormal' elevation of about eight kilometres. [...] So take away the spin and you take away all water at the equator. [...] The water that left the equatorial regions would have to go somewhere, and that 'somewhere' would be the poles. There would be two totally disconnected polar oceans on each side of the equatorial mega-continent.

All of this points to a very bad scenario for life on earth. The change, being so sudden, would kill pretty much everything.

If Earth gradually slowed down to a halt, over billions of years, then life has a chance. Animals could migrate over million of years and life in general would evolve to survive these changes. Temperatures would still be an issue, especially in the 6 months of day, but underground cave systems and oceans would likely still have plenty of life, being a safe refuge from the extreme temperatures of the surface.

EDIT: Added quote sources: https://image.gsfc.nasa.gov/poetry/ask/q1168.html https://www.australiangeographic.com.au/blogs/dr-karl-need-to-know/2018/05/what-would-happen-if-our-planet-stopped-spinning-entirely/

EDIT 2: As pointed out in the comments, for forgot a pretty important point: if Earth didn't have a magnetic field anymore, we would lose our main source of shielding from radiation. As a secondary effect, the Earth's atmosphere would probably be gone too, although I'm not sure how long this would take. For more info about that, I suggest checking out this article and its sources: https://whatifshow.com/what-if-earths-magnetic-field-disappeared/ I still believe it would be possible for some form of life to survive in closed cave systems, but that's my own hypothesis and I don't have any data to support it.

EDIT 3: Clarification: as pointed out in the comments, life wouldn't be completely gone. Major life forms would, but microbial life might still survive; stuff like bacteria and such can be found very deep underground, and might not be affected in a significant manner by this change.

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    $\begingroup$ As a further clarification, wouldn't the practically disappeared magnetosphere cause more radiation to flood onto the Earth, essentially killing most surface life and life close to the surface of the water? Regardless of fast or slow change? In addition, no Northern lights anymore. $\endgroup$ – Trioxidane Feb 1 at 9:25
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    $\begingroup$ all due respect to your sourcem but "So the Earth's spin has pushed up this liquid water to an 'abnormal' elevation of about eight kilometres" is utter nonsense. Yes the earth is an oblate spheroid due to rotation, but the ocean is lifted exactly as much as the rock under it. Sealevel at the equator will not drop 8 km. $\endgroup$ – PcMan Feb 1 at 9:57
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    $\begingroup$ @PcMan See planet-earth-2017.com/sea-level for support of the idea that the sea bulge at the equator is due to spin. Graphs and calculations depict the level change with every degree of spin increase or decrease, and historical geological evidence and results of past changes. $\endgroup$ – Justin Thyme the Second Feb 1 at 15:55
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    $\begingroup$ @TheSquare-CubeLaw Done, thanks for pointing that out. $\endgroup$ – Mr_Bober Feb 1 at 16:06
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    $\begingroup$ The mass of the atmosphere actually blocks radiation fairly well. We wouldn't all immediately be irradiated if the magnetic field disappears. The field weakens and disappears periodically when it flips, and these events are not associated with mass extinctions. Loss of atmosphere due to solar winds would occur on geologic timescales. $\endgroup$ – Harabeck Feb 1 at 23:10
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If Earth stop rotating on its own axis it would mean that a single solar day would last exactly as long as a year. That is, the Sun in the sky will move as the Earth orbits around it.

This would alter the weather patterns in a very drastic way: 6 months of light and 6 months of darkness everywhere on the planet are not something negligible.

I think most if not all of the lifeforms relying on the Sun for energy won't survive such a change. Probably some of the mosses and lichens growing in the subpolar regions would do just fine and might start migrating toward more temperate regions as soon as the ecologic niches are left available in habitable regions. They could then sustain some sort of food chain, which would be forced to either migrate chasing the sun or hibernate for the long night.

On the other hand non Sun dependent life will thrive undisturbed.

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    $\begingroup$ I think a key question would be the effect of prolonged "high noon" over parts of the Earth. They would heat much more than any current desert. While water that boiled could precipitate elsewhere, the effect of baking the landscape could be drastic - limestone could be slaked, coal and peat burned, greatly increasing greenhouse warming. Which might not be regretted later that night... I don't really know the answer to this one. $\endgroup$ – Mike Serfas Feb 1 at 11:53
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No

If Earth stopped rotation it would mean it is essentially tidally-locked with the sun. This would mean you would have once face that is always facing the sun and would be baking hot, and the other side would never get any sunlight and would be freezing cold. The only life that could survive would be in a minute "twilight zone" region between the two extremes. Even then, life might struggle to adapt because there would no longer be any day-night cycle and no more seasons.

The tides will also stop. It depends on whether you get rid of the moon or not, because the presence of the moon would cause the earth to rotate on its own, though it would rotate much more slowly than it currently does.

The oceans would likely boil away or freeze due to the tidal locking, which would have disastrous consequences for whatever life survived in the twilight zone. We would also probably lose the atmosphere. Long-term I would say there would also be problems with the minute amount of plant and planktonic life in the twilight zones maintaining enough oxygen in the Earth's atmosphere.

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    $\begingroup$ note that tidally locked bodies keep rotating, else they could not show the same face to the central body while orbiting it $\endgroup$ – L.Dutch - Reinstate Monica Feb 1 at 7:13
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    $\begingroup$ Tidal locking requires a rotational period equal to the orbital period, not a total lack of rotation. A body which stopped rotating entirely could spontaneously become tidally locked, but it would take a very long time. $\endgroup$ – Nuclear Hoagie Feb 1 at 15:52
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    $\begingroup$ If the Earth stopped rotating due entirely to natural forces, the result would HAVE to be a tidally locked rotation. The only reason it would stop rotating completely is that it went PAST the equilibrium of a tidally locked rotation and some external force other than natural forces caused it to happen. Tidally locked is probably the inevitable destiny of Earth in the very long run, unless the Sun burns out or we are pulled into the Sun first. $\endgroup$ – Justin Thyme the Second Feb 1 at 16:31
  • $\begingroup$ @JustinThymetheSecond Hmm, how do planets that rotate in retrograde fit in with that? They seem to have gone well past 1-to-1 and all the way into the negatives. (Venus in particular seems interesting, since it's retrograde and also has less than 1 Venus-day per Venus-year. Long term, do we expect it to rotate faster to reach a tidally-locked-retrograde rotation speed, or slow down, passing through 0, to ultimately reach tidally-locked-prograde rotation speed?) $\endgroup$ – user3067860 Feb 1 at 17:09
  • $\begingroup$ @user3067860 What is your evidence that retrograde planets have actually flipped their rotation all the way through '0'? Do you have evidence that Venus is NOT increasing rotational speed to tidally locked, if indeed it is now spinning at less than tidally locked rotation? Are you saying that it could go right through tidally locked and then through 0 and into spinning in the opposite direction? $\endgroup$ – Justin Thyme the Second Feb 1 at 17:31

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