Watching a highly entertaining piece of disaster porn the other day - What If The Earth Stops Spinning? (over a 5-year period)
Entertaining though it might be, there were a number of things in the film that struck me as scientifically dubious, so I thought I’d harness the collective scientific wisdom of the Dope on the question - just how accurate is this?
My first big problem: they make much of the fact that the force of the Earth’s spin makes it, its oceans, and its atmosphere, form an oblate spheroid, fatter at the equator (by about 20km). So as the spin decreases, in the movie, the oceans and atmosphere start assuming a more circular shape, essentially flowing to the poles and leaving a great belt of land circling the equator, poking out 20km more than before.
BUT - wouldn’t the land also settle quite quickly into a circle? It’s a fairly thin crust on top of a huge lake of magma - it doesn’t have that much structural stability.
Also - the claim is that temperatures eventually start to vary far more widely than they do today. Fair enough, but they have ranges like “minus one hundred Centigrade, up to as much as fifty-five”. That strikes me as wildly optimistic on the high end. Fifty five centigrade is only about twenty degrees higher than an absolutely ordinary Melbourne summer day - is that all it would get to? Would long nights and long days really lead to a lower *average *temperature? I find it hard to believe.
(there’s plenty of other dubious moments - the oceanographers taking bunnies to the newly risen equatorial continent, as if they’re going to be able to grow grass there after a few million years on the ocean floor is an eyebrow raiser, as is the English Channel not being able to make up its mind if it’s going down or up. But those questions will do to be getting on with)
Well, a sphere. I agree that it’s highly dubious that the Earth would act as if it were rigid.
Also note that if it did, the “equatorial continent” (even at “only”, say, 10km above sea level) is far above an altitude where life is sustainable for humans and pretty much anything that breathes air.
The material that makes up the mantle, which is much of the volume of the earth, is solid when viewed at human time scales. It flows enough to become more or less separated by density over geologic time scales, but it wouldn’t settle fast.
As far as “hot rock components of the earth” go, magma is unusual in its low viscosity, having gotten hot without being under the pressure that the innards of the earth are generally experiencing. It is not typical of what you find in the mantle.
It seems like the whole earth itself would shrink due to the increased effects of gravity.
But then again, volcanoes would be erupting like crazy due to the Earths crust being pushed closer to the core. All that pressure being applied under the crust has gotta go somewhere.
That’s why people are talking about this new equatorial continent. The lack of spinning would cause a redistribution of mass, but you’re claiming overall shrinking, which would require a reduction in total mass.
Equatorial gravity would increase slightly (by 0.5%), so the Earth would contract slightly because of the greater weight over the core. Heavier planets are more compact.
I can’t imagine any realistic scenario where this would cause more volcanism than the effects of the force required to slow the Earth down, however. If we ignore this (as I presume the program in the original post did) then there will be considerable geological disturbance as the new 20km high plateau around the equator settles back into the geoid.
I think the point is that the lack of spinning wouldn’t cause a redistribution of mass – at least not right away. The air would redistribute quickly, the water soon after, but the rock would take quite some time because it’s a lot more rigid than the other two.
In the interim, the equatorial bulge that currently exists due to the centrifugal force would still be there, and since the water and air have left the premises, it will be more noticeable on the ground.
Hmm; once again I’ve expressed myself badly here. ‘Heavier planets are more compact’ is not the best way to put it. What I mean to say is that assuming that the planet retains the same composition, a heavier planet is more dense than a lighter planet. Since effective gravity has increased on a non-spinning Earth, the weight acting on the centre is greater, even though the mass is not. So the material at the centre will be more compact, making the planet slightly smaller.
Ignorance fought - I had been under the impression that the mantle was more or less all mantle, and that it was just the core that’s solid.
Still…20km is not that much compared to the size of the earth, and that would be all that you’d need to let the crust settle (particularly if there’s volcanic activity). Is there not even as much liquid magma at the top of the mantle as that?
The recovery process would take thousands of years. Much of the northern hemisphere is still recovering from the weight of the last ice age, and that ended ten thousand years ago or so.
In fact, the mantle is 100% mantle. Beneath the mantle is a liquid outer core, and beneath that is a solid inner core.
Magma is not all in a “layer” at the top of the mantle. It forms in places, but the crust and mantle is mostly solid. I recently learned the term “Rheid” which describes the state that the mantle is in.
We’ll be in a lot more trouble from the effects on the biosphere. Half the planet can no longer carry out photosynthesis to any significant extent. The other half is subjected to unending day and disruption of all circadian and likely seasonal rhythms. Agriculture crashes, species extinction skyrockets, cities plunged into eternal darkness…there goes civilization.
Not the assumption that is being made. You’re assuming the Earth is tidally locked and actually spins once per year to keep the same face towards the Sun. The assumption in the OP’s video is that it doesn’t spin at all, so that you have a “day” one year long. Never mind how such a situation would occur. I’ll admit that this would also be incredibly severe, and untenable for our current biosphere.
Does the Earth “stop spinning” in the sense that it is now tidally locked to the sun? Because the Earth is still spinning there, it’s just that a rotation now takes a year and so the sun never changes position when viewed from a point on the Earth.
Or, is the Earth not spinning with respect to the fixed stars? That means the sun gradually traverses the sky over the course of the year, and we have 6 month days and 6 month nights. If the Earth retains its axial tilt, then depending on what time of year the Earth gets stopped one of the poles may be pointed towards the Sun and one away, and we’d have a constant day pole and a constant night pole. Or if it was at the equinox, we’d have a funky result at the poles of the sun traveling around the horizon slowly over the year.
The problem with the tidal locking is that the sun side would get so hot the oceans would boil, while the dark side would get so cold the atmosphere might start to freeze out. So there’d be a baked airless desert on the sun side, and a giant glacier on the dark side. If the glacier is warm enough it might flow and you’d have a ring of melting glacier at the terminus. But if it’s cold enough then the ice becomes rigid and pretty soon there’s no more liquid water on Earth except a few hot spots under the ice.
Beneath the mantle is a liquid outer core, and beneath that is a solid inner core.