<h3>No.</h3>
<ul>
<li>I'm not aware of any evidence that Earth ever rotated in the opposite direction in the past.</li>
<li>It's very unlikely that it will have its direction reversed, e.g. by a very large bolide, in the future.</li>
</ul>
<p>For future reversals, I can think of 2 scenarios: slowing down and reversing, or flipping the rotational axis.</p>
<h3>Slow down and reverse</h3>
<p>I think we can discount the case of reversal by abruptly (in the geological sense) stopping it then accelerating in the opposite sense. For example, assuming the Earth has <a href="https://en.wikipedia.org/wiki/Rotational_energy" rel="nofollow noreferrer">rotational kinetic energy</a> of 2 × 10<sup>29</sup> J, reversing its direction would require a change of twice this number. This is at least a million times the energy released in <a href="https://en.wikipedia.org/wiki/Chicxulub_crater" rel="nofollow noreferrer">the Chicxulub impact</a> (about 3×10<sup>23</sup> J).</p>
<p>This is all very rough, we're ignoring its total orbital momentum and assuming its a spherical solid, but it seems like it would be hard to find this much energy, especially in today's solar system.</p>
<p>There's <a href="https://earthscience.stackexchange.com/questions/236/will-the-earth-ever-stop-rotating">an old question</a> about the possibility of the Earth eventually running out of angular momentum. If you accept that this might happen in several (probably tens of) billions of years, then I suppose it could be started again by a bolide impact... except that bolide impacts will be impossibly rare events by then.</p>
<h3>Flip the axis</h3>
<p>Most of the answers I could find are just as speculative as the question itself, and they seem to focus on a reversal of rotation direction. But none of them address the possibility of the Earth's axis flipping 180 degrees with respect to the ecliptic, which would effectively reverse the rotation. (Really, since it's already titled by 23.4 degrees, only another 68 degrees would push the North pole over the ecliptic.). There's <a href="https://physics.stackexchange.com/questions/613448/energy-required-to-tilt-earth-s-axis-by-90-degrees">a Physics Stack Exchange</a> question about this, and thanks to the <a href="https://en.wikipedia.org/wiki/Gyroscope" rel="nofollow noreferrer">gyroscope</a> effect, the energy required to shift the axis is almost the same as that required to reverse the spin.</p>
<p>Conclusion: this is just as unlikely as the first scenario.</p>
<h3>Further reading</h3>
<ul>
<li>There's a good thread on all this <a href="https://astronomy.stackexchange.com/questions/40768/will-earth-rotate-backwards-in-the-future">over on the Astronomy Stack Exchange</a>.</li>
<li>Here's <a href="https://indd.adobe.com/view/f6592f4d-f2e3-4315-8afc-1b6f9588040f" rel="nofollow noreferrer">a poster</a> about how climate would be affected by a reverse-rotating Earth.</li>
<li>There's <a href="https://physics.stackexchange.com/questions/29235/would-it-matter-if-the-earth-rotated-clockwise">a Physics Stack Exchange</a> question about what else would be affected.</li>
</ul>

CC BY-SA 4.0
2022-04-08T13:56:33.380Z
I think you've given the formula for torque, not work - the energy required to flip the earth's rotation shouldn't depend on how long it takes to do it, it should just be double the value of the earth's current rotational kinetic energy. And if we're assuming this is the result of an impact, the acceleration time will be on the order of a second, not a year (although the time will just determine the power needed, not the total energy requirement).
Nuclear Hoagie
CC BY-SA 4.0
2022-04-08T16:25:00.833Z
@NuclearHoagie Admittedly I didn't give it a massive amount of thought, I probably got confused about angular momentum. Please feel free to edit or create another answer with a better analysis. As for the year, definitely a fair point. Somehow I couldn't imagine it taking ~1s but I guess it would have to be ~instantaneous. I think then it would exceed the binding energy and bash us out of orbit and/or into smithereens. Either way, it's bad.
Matt Hall
CC BY-SA 4.0
2022-04-08T16:27:59.560Z
@NuclearHoagie Okay, I tried casting in terms of kinetic energy... see what you think. Definitely simpler.
Matt Hall
CC BY-SA 4.0
2022-04-08T13:43:19.427Z
2022-04-08T16:27:27.633Z
2022-04-08T16:27:27.633Z
Matt Hall
<p>We know that the earth is rotating from west to east (anti-clockwise) Has the earth ever rotated from east to west in past,in early times after earth has formed?  And/or is there any scientific foresight that the earth  may rotate from east to west (clockwise) in future?
If it happens,what changes would occur?</p>

CC BY-SA 4.0
2022-04-08T13:45:06.947Z
have you done any research trying to find an answer to this question like looking here https://solarsystem.nasa.gov/solar-system/our-solar-system/in-depth/
trond hansen
CC BY-SA 4.0
2022-04-08T15:25:59.747Z
"Clockwise" and "anti-clockwise" are meaningless here, because it all depends on which pole you're looking down on. "East" and "west" are defined by sunrise and sunset, so they don't help either. The terms "prograde" and "retrograde" (i.e. rotation relative to orbit) do actually mean something.
Spencer
CC BY-SA 4.0
2022-04-08T16:27:43.380Z
@Spencer There are different definitions of east and west, they can either be defined by rotation or with respect to the ecliptic. Venus is very commonly described as having a western sunrise, although I agree there are more precise terms.
Nuclear Hoagie
CC BY-SA 4.0
2022-04-08T16:34:50.233Z
@NuclearHoagie But if you look at just the etymology of the words, you'll see they're related to sunrise/sunset or morning/evening.
Spencer
CC BY-SA 4.0
2022-04-11T12:51:53.490Z
I’m voting to close this question because it likely belongs in astronomy.stackexchange.com. There is even a very related question there: https://astronomy.stackexchange.com/questions/40768/will-earth-rotate-backwards-in-the-future
arkaia
<earth-rotation>
We know that the earth is rotating from west to east.Has the earth ever rotated from east to west in past,or any possibilty it may in future?
S. Y.
# We know that the earth is rotating from west to east.Has the earth ever rotated from east to west in past,or any possibilty it may in future?

(Asked by: username_0 on 2022-04-08)

We know that the earth is rotating from west to east (anti-clockwise) Has the earth ever rotated from east to west in past,in early times after earth has formed? And/or is there any scientific foresight that the earth may rotate from east to west (clockwise) in future?
If it happens,what changes would occur?

**Tags:** earth-rotation

> **Comments:**
> **username_1**: have you done any research trying to find an answer to this question like looking here https://solarsystem.nasa.gov/solar-system/our-solar-system/in-depth/  
> **username_2**: "Clockwise" and "anti-clockwise" are meaningless here, because it all depends on which pole you're looking down on. "East" and "west" are defined by sunrise and sunset, so they don't help either. The terms "prograde" and "retrograde" (i.e. rotation relative to orbit) do actually mean something.  
> **username_3**: @username_2 There are different definitions of east and west, they can either be defined by rotation or with respect to the ecliptic. Venus is very commonly described as having a western sunrise, although I agree there are more precise terms.  
> **username_2**: @username_3 But if you look at just the etymology of the words, you'll see they're related to sunrise/sunset or morning/evening.  
> **username_4**: I’m voting to close this question because it likely belongs in astronomy.stackexchange.com. There is even a very related question there: https://astronomy.stackexchange.com/questions/40768/will-earth-rotate-backwards-in-the-future  

---

## 1 answers

### Answer by username_5 on 2022-04-08. Score: 3

### No.

* I'm not aware of any evidence that Earth ever rotated in the opposite direction in the past.
* It's very unlikely that it will have its direction reversed, e.g. by a very large bolide, in the future.

For future reversals, I can think of 2 scenarios: slowing down and reversing, or flipping the rotational axis.

### Slow down and reverse

I think we can discount the case of reversal by abruptly (in the geological sense) stopping it then accelerating in the opposite sense. For example, assuming the Earth has [rotational kinetic energy](https://en.wikipedia.org/wiki/Rotational_energy) of 2 × 1029 J, reversing its direction would require a change of twice this number. This is at least a million times the energy released in [the Chicxulub impact](https://en.wikipedia.org/wiki/Chicxulub_crater) (about 3×1023 J).

This is all very rough, we're ignoring its total orbital momentum and assuming its a spherical solid, but it seems like it would be hard to find this much energy, especially in today's solar system.

There's [an old question](https://earthscience.stackexchange.com/questions/236/will-the-earth-ever-stop-rotating) about the possibility of the Earth eventually running out of angular momentum. If you accept that this might happen in several (probably tens of) billions of years, then I suppose it could be started again by a bolide impact... except that bolide impacts will be impossibly rare events by then.

### Flip the axis

Most of the answers I could find are just as speculative as the question itself, and they seem to focus on a reversal of rotation direction. But none of them address the possibility of the Earth's axis flipping 180 degrees with respect to the ecliptic, which would effectively reverse the rotation. (Really, since it's already titled by 23.4 degrees, only another 68 degrees would push the North pole over the ecliptic.). There's [a Physics Stack Exchange](https://physics.stackexchange.com/questions/613448/energy-required-to-tilt-earth-s-axis-by-90-degrees) question about this, and thanks to the [gyroscope](https://en.wikipedia.org/wiki/Gyroscope) effect, the energy required to shift the axis is almost the same as that required to reverse the spin.

Conclusion: this is just as unlikely as the first scenario.

### Further reading

* There's a good thread on all this [over on the Astronomy Stack Exchange](https://astronomy.stackexchange.com/questions/40768/will-earth-rotate-backwards-in-the-future).
* Here's [a poster](https://indd.adobe.com/view/f6592f4d-f2e3-4315-8afc-1b6f9588040f) about how climate would be affected by a reverse-rotating Earth.
* There's [a Physics Stack Exchange](https://physics.stackexchange.com/questions/29235/would-it-matter-if-the-earth-rotated-clockwise) question about what else would be affected.

> **Comments:**
> **username_3**: I think you've given the formula for torque, not work - the energy required to flip the earth's rotation shouldn't depend on how long it takes to do it, it should just be double the value of the earth's current rotational kinetic energy. And if we're assuming this is the result of an impact, the acceleration time will be on the order of a second, not a year (although the time will just determine the power needed, not the total energy requirement).  
> **username_5**: @username_3 Admittedly I didn't give it a massive amount of thought, I probably got confused about angular momentum. Please feel free to edit or create another answer with a better analysis. As for the year, definitely a fair point. Somehow I couldn't imagine it taking ~1s but I guess it would have to be ~instantaneous. I think then it would exceed the binding energy and bash us out of orbit and/or into smithereens. Either way, it's bad.  
> **username_5**: @username_3 Okay, I tried casting in terms of kinetic energy... see what you think. Definitely simpler.  

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