# What if the Earth Spun in the Opposite Direction **URL:** \ **Category:** Factual Questions\ **Created:** [November 5, 2024, 8:45am UTC](https://boards.straightdope.com/t/what-if-the-earth-spun-in-the-opposite-direction/1009710 "2024-11-05T08:45:42Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [November 5, 2024, 6:03pm UTC](https://boards.straightdope.com/t/what-if-the-earth-spun-in-the-opposite-direction/1009710/21 "2024-11-05T18:03:58Z")
> [@Horatius](#): > > The Moon currently shifts its rising time later by about an hour every day. If the Earth were to spin in the opposite direction, then the Moon would rise about an hour _earlier_ every day, which would have a big change on the tide schedule. So everything that relies on that schedule would be different, to at least some extent. If Earth had spun in the opposite direction right from the get-go, animals might have evolved a bit differently. But if it suddenly went the other way tomorrow, I wonder how animals and plants that are adapted for life in the intertidal zone would do with the tides rolling in/out on a faster schedule. ---
**Author:** ![Stranger\_On\_A\_Train](https://avatars.discourse-cdn.com/v4/letter/s/13edae/32.png) [@Stranger\_On\_A\_Train](https://boards.straightdope.com/u/Stranger_On_A_Train)\ **Post date:** [November 5, 2024, 6:26pm UTC](https://boards.straightdope.com/t/what-if-the-earth-spun-in-the-opposite-direction/1009710/22 "2024-11-05T18:26:29Z")
> [@Ynnad](#): > > What would have happened if the Earth spun in the opposite direction, _i.e_., the sun came up in the west, but everything else was the same. Larry Niven would not need to [correct the first paperback printing of _Ringworld_](https://scifi.stackexchange.com/questions/896/what-were-the-mistakes-in-the-first-paperback-edition-of-ringworld). Stranger ---
**Author:** ![DPRK](https://avatars.discourse-cdn.com/v4/letter/d/4491bb/32.png) [@DPRK](https://boards.straightdope.com/u/DPRK)\ **Post date:** [November 5, 2024, 6:26pm UTC](https://boards.straightdope.com/t/what-if-the-earth-spun-in-the-opposite-direction/1009710/23 "2024-11-05T18:26:56Z")
I do not know enough about this, at least definitely not off the top of my head. The obvious example of a planet spinning backwards is Venus. But, how did Venus end up that way? Wiktionary suggests atmospheric tides. Now, we know that the Moon’s tides are slowing down the rotation of the Earth, not that it can stop or reverse it. However, we can imagine the Earth _already_ spinning retrograde when whatever event created the Moon happened. What happens then?? Perhaps something to throw into a rough simulation… ---
**Author:** ![scudsucker](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/scudsucker/32/14101_2.png) [@scudsucker](https://boards.straightdope.com/u/scudsucker)\ **Post date:** [November 5, 2024, 6:33pm UTC](https://boards.straightdope.com/t/what-if-the-earth-spun-in-the-opposite-direction/1009710/24 "2024-11-05T18:33:10Z")
> [@penultima\_thule](#): > > Gawd knows whether the Indian sub-continent and the monsoonal weather engine of the Himalyas bumps into the bottom of South Africa and creates a landbridge to Antarctica I had never considered the coriolis force to have affected plate tectonics, but thinking about how we all float around on liquid magna it makes sense. I mean, in addition to various other forces and inertia. Thanks for the insight. ETA, seems I was presumptive. Dankie, @MrDibble ---
**Author:** ![Horatius](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/horatius/32/3572_2.png) [@Horatius](https://boards.straightdope.com/u/Horatius)\ **Post date:** [November 5, 2024, 6:43pm UTC](https://boards.straightdope.com/t/what-if-the-earth-spun-in-the-opposite-direction/1009710/25 "2024-11-05T18:43:40Z")
> [@DPRK](#): > > However, we can imagine the Earth _already_ spinning retrograde when whatever event created the Moon happened. What happens then?? Well, we’re still not absolutely sure [what created the Moon](https://www.nhm.ac.uk/discover/how-did-the-moon-form.html#:~:text=The%20giant%2Dimpact%20theory%20is,Earth%20to%20form%20the%20Moon.), but: > - **The giant-impact theory** is most widely accepted today. This proposes that the Moon formed during a collision between the Earth and another small planet, about the size of [the planet Mars](https://www.nhm.ac.uk/discover/planet-mars.html). The debris from this impact collected in an orbit around Earth to form the Moon. If this is how the Moon was formed, then its direction of orbit would most likely match the direction of spin of the Earth, so things would be the same, just mirror-imaged to what we have now. If one of the other theories is what really happened, then it’s probably a coin flip as to whether the orbit matches the spin, or not. ---
**Author:** ![John\_DiFool](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_difool/32/19543_2.png) [@John\_DiFool](https://boards.straightdope.com/u/John_DiFool)\ **Post date:** [November 5, 2024, 6:57pm UTC](https://boards.straightdope.com/t/what-if-the-earth-spun-in-the-opposite-direction/1009710/26 "2024-11-05T18:57:35Z")
Just wanted to note the OP’s handle/thread topic synchrony. ---
**Author:** ![md-2000](https://avatars.discourse-cdn.com/v4/letter/m/9d8465/32.png) [@md-2000](https://boards.straightdope.com/u/md-2000)\ **Post date:** [November 5, 2024, 9:03pm UTC](https://boards.straightdope.com/t/what-if-the-earth-spun-in-the-opposite-direction/1009710/27 "2024-11-05T21:03:13Z")
> [@scudsucker](#): > > I had never considered the coriolis force to have affected plate tectonics, but thinking about how we all float around on liquid magna it makes sense. I mean, in addition to various other forces and inertia. The North American and South American continents drifted away from Africa and are creating the mountain ranges on the west side of each continent as they collide and override the Pacific plates (simplified version). Presumably their drift direction is somehow tied to earth’s rotation? OTOH India is drifting north-eastward and Australia below the equator north-westaward? ---
**Author:** ![whc.03grady](https://avatars.discourse-cdn.com/v4/letter/w/a6a055/32.png) [@whc.03grady](https://boards.straightdope.com/u/whc.03grady)\ **Post date:** [November 6, 2024, 5:19am UTC](https://boards.straightdope.com/t/what-if-the-earth-spun-in-the-opposite-direction/1009710/28 "2024-11-06T05:19:34Z")
I read someone, Stephen Jay Gould maybe, who said Venus doesn’t spin backwards, but rather it’s upside-down. (As a paleontologist, he was repeating from another source but I don’t remember who.) ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [November 6, 2024, 6:11am UTC](https://boards.straightdope.com/t/what-if-the-earth-spun-in-the-opposite-direction/1009710/29 "2024-11-06T06:11:04Z")
> [@whc.03grady](#): > > I read someone, Stephen Jay Gould maybe, who said Venus doesn’t spin backwards, but rather it’s upside-down. There’s not really any difference between those two positions. Venus would normally be tidally locked to the Sun, but there’s some tidal effect on its dense atmosphere that caused it to overshoot tidal locking by a small amount. Hence it rotates slowly backwards. ---
**Author:** ![MrDibble](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mrdibble/32/114_2.png) [@MrDibble](https://boards.straightdope.com/u/MrDibble)\ **Post date:** [November 6, 2024, 9:07am UTC](https://boards.straightdope.com/t/what-if-the-earth-spun-in-the-opposite-direction/1009710/30 "2024-11-06T09:07:02Z")
> [@md-2000](#): > > Presumably their drift direction is somehow tied to earth’s rotation? Nope. For instance, you’re looking at the Eastern edge of the [Pacific plate](https://en.wikipedia.org/wiki/Pacific_plate) (for North America) and thinking it’s significant, but the plate is subducting under the Aleutians (E-W axis) too. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [November 6, 2024, 9:15am UTC](https://boards.straightdope.com/t/what-if-the-earth-spun-in-the-opposite-direction/1009710/31 "2024-11-06T09:15:19Z")
Yeah, when I mentioned it, I had sort of misunderstood the OP to be asking _what if the Earth had **always** spun that way_. I think the coriolis forces would have _some_ effect on the way continental plates form and change, if those forces were applied over geological spans of time. But it’s kind of a moot point because if you started with two identical proto-earths, both spinning in the same direction and left them for billions of years, you’d end up with two different continental maps anyway, just because there’s bound to be some chaos in the process. ---
**Author:** ![MrDibble](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mrdibble/32/114_2.png) [@MrDibble](https://boards.straightdope.com/u/MrDibble)\ **Post date:** [November 6, 2024, 9:24am UTC](https://boards.straightdope.com/t/what-if-the-earth-spun-in-the-opposite-direction/1009710/32 "2024-11-06T09:24:51Z")
One thing I should clarify - I didn’t say the Earth’s rotation has no effect on tectonics, I said the Coriolis force has no effect. The equatorial bulge _might_ have a slight impact on preferred direction for things and that’s also a result of rotation, but that’s centrifugal force at play, not Coriolis force, and a mere change in direction would make no difference there, as the magnitude would stay the same and we should expect the same equatorial bulge. ---
**Author:** ![whc.03grady](https://avatars.discourse-cdn.com/v4/letter/w/a6a055/32.png) [@whc.03grady](https://boards.straightdope.com/u/whc.03grady)\ **Post date:** [November 6, 2024, 9:56am UTC](https://boards.straightdope.com/t/what-if-the-earth-spun-in-the-opposite-direction/1009710/33 "2024-11-06T09:56:00Z")
The difference, which is significant, would be that either (a) Venus used to spin the same way as does Earth when viewed from above, slowed down to a stop, and then began spinning the other way; or (b) Venus used to spin the same way as does Earth when viewed from above, and then flipped over, maintaining its direction of spin all the while. ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [November 6, 2024, 10:08am UTC](https://boards.straightdope.com/t/what-if-the-earth-spun-in-the-opposite-direction/1009710/34 "2024-11-06T10:08:50Z")
> [@md-2000](#): > > The North American and South American continents drifted away from Africa and are creating the mountain ranges on the west side of each continent as they collide and override the Pacific plates (simplified version). Presumably their drift direction is somehow tied to earth’s rotation? Seems unlikely to me. Any north-south continental drift is so slow - a few inches per year at best - that any east-west velocity component a tectonic plate might exhibit has millions of years over which to adjust. ---
**Author:** ![Ynnad](https://avatars.discourse-cdn.com/v4/letter/y/4491bb/32.png) [@Ynnad](https://boards.straightdope.com/u/Ynnad)\ **Post date:** [November 6, 2024, 11:06am UTC](https://boards.straightdope.com/t/what-if-the-earth-spun-in-the-opposite-direction/1009710/35 "2024-11-06T11:06:57Z")
> [@Mangetout](#): > > … I had sort of misunderstood the OP to be asking _what if the Earth had **always** spun that way_. That **is** what I was thinking about, what if the Earth had always spun that way, Why am I awake at 4:00 a.m.? ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [November 6, 2024, 11:13am UTC](https://boards.straightdope.com/t/what-if-the-earth-spun-in-the-opposite-direction/1009710/36 "2024-11-06T11:13:14Z")
Thank you for the clarification; it’s kind of hard to formulate a thought experiment in which the spin is the only thing that would be different - if you started with _any_ identical proto-earth and ran the thing for billions of years, you would end up with some earth-like planet, but with a very different map, just because of the chaotic nature of the formative processes. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [November 6, 2024, 11:13am UTC](https://boards.straightdope.com/t/what-if-the-earth-spun-in-the-opposite-direction/1009710/37 "2024-11-06T11:13:58Z")
> [@whc.03grady](#): > > The difference, which is significant, would be that either (a) Venus used to spin the same way as does Earth when viewed from above, slowed down to a stop, and then began spinning the other way; or (b) Venus used to spin the same way as does Earth when viewed from above, and then flipped over, maintaining its direction of spin all the while. Or (c): Venus formed spinning the way it does now. IOW opposite most of the rest of the solar system. ---
**Author:** ![Ynnad](https://avatars.discourse-cdn.com/v4/letter/y/4491bb/32.png) [@Ynnad](https://boards.straightdope.com/u/Ynnad)\ **Post date:** [November 6, 2024, 11:25am UTC](https://boards.straightdope.com/t/what-if-the-earth-spun-in-the-opposite-direction/1009710/38 "2024-11-06T11:25:26Z")
> [@Mangetout](#): > > … just because of the chaotic nature … I guess we would have to sort of ignore the chaos to get anywhere with this thought experiment. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [November 6, 2024, 11:50am UTC](https://boards.straightdope.com/t/what-if-the-earth-spun-in-the-opposite-direction/1009710/39 "2024-11-06T11:50:36Z")
As covered in some of the earlier threads, it really depends on what you assume is different and what you assume is the same. Heck, if we started with the exact same molten proto-Earth / Moon system from ~4B years ago spinning the way it does now and re-ran the experiment up to today it’s a statistical certainty the continents, climate, life, etc., would be vastly different than what we see outside. The movie we call “planetary history” could have unfolded lots of different ways and we only get to see this one version. To that mix, adding opposite spin would IMO be like adding a pinch of salt to a giant industrial batch of spaghetti sauce. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [November 6, 2024, 3:30pm UTC](https://boards.straightdope.com/t/what-if-the-earth-spun-in-the-opposite-direction/1009710/40 "2024-11-06T15:30:49Z")
One thing that would be different is that a sidereal day would be 4 minutes longer than a solar day, instead of shorter. Astronomers would care about this. [Previous page](https://boards.straightdope.com/t/what-if-the-earth-spun-in-the-opposite-direction/1009710.md?page=1) [Next page](https://boards.straightdope.com/t/what-if-the-earth-spun-in-the-opposite-direction/1009710.md?page=3)