What would happen if Earths core cooled down

[PlasmaSphere]

If Earths core cooled down completely what would be the effects on the Formation of Earth?

I think that eventually, over millions of years, the enitre surface of the Earth would be covered in water, a huge ocean. There would be no new mountains being formed, and eventually errosion from rain would erode every protruding part of the Earth's surface until the surface was so flat the entire Earth would be covered by water. Similar to what Europa looks like, a big ball of ice.

Could that happen?

 

[DaveC426913]

It is partly the heat in the Earth's centre that drives water to the surface. Without heat, the Earth would be a dry ball of rock.

 

[DrClapeyron]

The Earth would shrink a bit, after the core begins providing heat to the mantle both core and mantle would turn solid and contract from their liquidis state. Don't know exactly what would happen to the surface or the plates, though I imagine buoyancy would no longer be of any consequence.

 

[Andre]

http://adsabs.harvard.edu/abs/2004GeoJI.158..470V0 that the spin axis of solid Earth inner core is lagging the precession of the equinoxes. This would call for a magnetic coupling in the liquid outer core between the solid inner core and the mantle.

Now if the inner Earth was to cool down, perhaps we should include philosophizing about the consequenses for this effect. The liquid outer core would solidify likely at the area of the greatest pressure, at the inner core boundary. This may have two consequences for the core mantle coupling, the angular momentum of the inner core would increase while taking up the angular momentum of the solidifying outer core and perhaps that the reduced convection in the liquid outer core could weaken the magnetic coupling.

Because the increased momentum requires more torque force from the hypothetically weakening magnetic forces in the outer core, the difference in precession between inner core and mantle may increase hypothetically, which could result in greater misalignment of the inner core and mantle spin axes. This is likely to generate unusual flows in the liquid outer core with all kind of unpredictable effects. One of them might be increased friction and hence conversion of rotational energy into heat, which would heat up the core again??

More thoughts about that here:

http://www.me.ucsb.edu/dept_site/vanyo/core_mantle.pdf
http://www.me.ucsb.edu/dept_site/vanyo/computational.pdf

http://www.imcce.fr/Equipes/ASD/preprints/prep.2002/venus1.2002.pdf
(para 3.2)

So all this is nothing new actually, but all the consequences may not have been taken into account when judging the history of Earths past. But that would be speculation.

 

[matthyaouw]

We'd lose the magnetic field of the earth, for one.

 

[billiards]

The Earth would shrink a bit, after the core begins providing heat to the mantle both core and mantle would turn solid and contract from their liquidis state. Don't know exactly what would happen to the surface or the plates, though I imagine buoyancy would no longer be of any consequence.

I have to pick you up on a common misconception you seem to have picked up. The mantle is not liquid. It can sustain shear waves, which implies that it has rigidity. In fact, the mantle is visco-elastic; it behaves as a solid over short time-scales but deforms as a very viscous fluid over geological time.

I think you are right about the Earth would shrink slightly, because presumably the outer core would solidify. An immediate consequence of this would be the loss of the geomagnetic field, I believe the atmosphere would then be exposed to the solar wind (previously kept at bay by the geomagnetic field) and much of it would be stripped away, this would be very detrimental to life on our planet. We might also, after some time, expect to see an end to earthquakes and volcanism - the plates would stop moving and the planet would become all but geologically dead. Provided that the planet does not lose all its water to space, I imagine that eventually erosion would sculpt the Earth into a much smoother object than it is now, hence the surface could be covered in water. I have some doubts that this could happen though, if the atmosphere is stripped away, what mechanisms would be responsible for the erosion of high mountains? Furthermore, it seems likely to me that the planet would eventually lose its water to space, possibly by some kind of runaway greenhouse effect as seems to have happened to Venus.

 

[Andre]

I think you are right about the Earth would shrink slightly, because presumably the outer core would solidify.

But think about how. Solidifying would happen either by losing heat or decreasing pressure. As long heat is transported from in- to out, the most cooling is done at the inner core and hence, isn't that where the solidification would logically have take place? So what would that imply?

We assume that the http://www.sciencemag.org/cgi/content/abstract/274/5294/1883. If the core compresses due to cooling while, maintaining angular momentum, it will spin up some more (spinning ice skater effect). Furthermore, it appears that the spin axes of the inner core lags in precession, see the Vanyo link in my previous post. How would the possibly quite differently spinning solidifying inner core meet the core mantle boundary and attach to complete the solidification process, with those spinning differences?

Or could those spinning differences lead to continuous friction in the last remaining liquid portion of the core, decreasing the spinning rate? Would it be required that the spinning virtually stopped first before the core could solidify completely, which may likely be leading to the loss of magnetic field and perhaps eventually to no more tectonic activity?

Hey, isn't there a planet around that answers to those specific end results?
Just asking questions, not developing theory.

Note that Correia et al appear to ignore the thermodynamic implications of friction in the core. Do read para 3.2.

 

[billiards]

But think about how. Solidifying would happen either by losing heat or decreasing pressure. As long heat is transported from in- to out, the most cooling is done at the inner core and hence, isn't that where the solidification would logically have take place?

But, umm, the inner core is already solid.

We assume that the http://www.sciencemag.org/cgi/content/abstract/274/5294/1883. If the core compresses due to cooling while, maintaining angular momentum, it will spin up some more (spinning ice skater effect). Furthermore, it appears that the spin axes of the inner core lags in precession, see the Vanyo link in my previous post. How would the possibly quite differently spinning solidifying inner core meet the core mantle boundary and attach to complete the solidification process, with those spinning differences?

I dislike thinking of the inner sore as spinning completely separately from the rest of the earth, sure there is a minor amount of super rotation (I think recent work has found this to be something like 0.1 degree per year faster than the crust - an order of magnitude lower than the initial study found in the 70s), but its not much really, and the outer core has the viscosity of water, and is > 2000 km thick, so in all seriousness there is not going to be much friction between the inner core and the mantle. (remember, the inner core is the thing that is super-rotating - the outer core has convection currents that look like corkscrews pointing down the Earth's spin axis)

Actually, I can't really take this question too seriously, because it is completely unphysical that the core would just cool. It would take billions and billions of years and the planet would just gradually grind to a halt. If the core suddenly shrunk there would be a massive earthquake and so much heat would be generated that I wouldn't be surprised if the core partially melted again.

 

[Andre]

But, umm, the inner core is already solid.

Come on. Is it that that difficult? Today the solid inner core radius is somewhere about1250 km, in the next century it could be 1260 km due to cooling and solidifying in another century it could be 1300 km. What's so difficult about imagining a growing inner core due to cooling??

I dislike thinking of the inner sore as spinning completely separately from the rest of the earth, sure there is a minor amount of super rotation (I think recent work has found this to be something like 0.1 degree per year faster than the crust - an order of magnitude lower than the initial study found in the 70s), but its not much really,

300 years for one revolution I seem to remember. Not much, but image halting a mammoth tanker.

Actually, I can't really take this question too seriously, because it is completely unphysical that the core would just cool. It would take billions and billions of years and the planet would just gradually grind to a halt. If the core suddenly shrunk there would be a massive earthquake and so much heat would be generated that I wouldn't be surprised if the core partially melted again.

certainly. That melting and subsequent cooling might indeed happen...cyclicly. How about in an unexplained 100,000 years cycle we see nowadays, unrelated to the well known Milankovitch cycles? Just wondering.

 

[billiards]

Come on is it that that difficult? Today the solid inner core radius is somewhere about1250 km, in the next century it could be 1260 km due to cooling and solidifying in another century it could be 1300 km. What's so difficult about imagining a growing inner core due to cooling??

Well, if by inner core you meant inner core boundary (ICB) then fair enough, the inner core is crystallising out of solution albeit at a rate much, much slower than you seem to have in mind.

300 years for one revolution I seem to remember. Not much, but image halting a mammoth tanker.

That seems a bit quick, perhaps I will dig out my old uni notes on this to confirm, but I think you are working from the old study which has now been improved upon, I reckon you are an order of magnitude too quick - if it spins 0.1 of a degree per year faster than the earth, it takes 3600 years.

certainly. That melting and subsequent cooling might indeed happen...cyclicly. How about in an unexplained 100,000 years cycle we see nowadays, unrelated to the well known Milakovitch cycles? Just wondering.

No, just no! Perhaps if you stopped for a second to think about the geophysics you would realize how ridiculous this sounds.

 

[Andre]

I concede to be wrong it was one revolution in 400 years, not 300:

Song and Richards calculated that over a year, the inner core rotates about one longitudinal degree more than the Earth's mantle and crust. The inner core makes a complete revolution inside the Earth in about 400 years.

http://www.scienceblog.com/community/older/archives/C/archsf548.html

That challenge may get me banned (thanks Jack) since I can't find the peer reviewed reference. But I guess, it's worth it.

Please demonstrate what is ridiculous here,

 

[billiards]

Andre, I don't think that link will get you banned, I myself cannot find the study but I have it in my notes in front of me that there is 0.1 degrees of super rotation per year, so I will have to disagree with your link for the time being (so if they ban you they'll have to ban me too ).

It seems to me that you are looking for a solution to your "pulsating equator" hypothesis. Could the inner core be growing and collapsing cyclically? Could this explain an apparent 100,000 yr cycle that you yourself have observed, and that you yourself have hypothesized is consistent with a bulging earth, a so-called pulsating equator?

The answer is of course no, the inner core has been slowly crystallizing out of a liquid core since it started about 1.7 billion years ago. There is no evidence, or any physical basis to suggest that it has been growing and shrinking, or that it creates friction which causes whole Earth deformations. I think any talk of the deep Earth must involve a high degree of geophysics (involving highly rigorous interdisciplinary efforts e.g. seismology/mineral physics/geomagnetics/geodynamics etc..), afterall, it is the only real way we have of probing the deep Earth and provides the best models we as a species can possibly produce of our planet. To hypothesize about the inner workings of our planet without having a sound geophysical backing is where eyebrows get raised, and rightfully so. Perhaps you could explain how this happens, geophysically, if you wish to uphold your argument:

That melting and subsequent cooling might indeed happen...cyclicly

 

[Andre]

But what is the ridiculous part?

Here is a http://science-mag.aaas.org/cgi/content/short/273/5274/428 for the faster spinning inner core, a hypothesis which is based on changing propagation speeds of East west oriented P/S waves. The most recent rate I could find is 0.3 - 0.5 degrees a year.

Much more important than that could be a possible misalignment of the spin axes between inner core and mantle (Vanyo 2004) due to different precession parameters which might increase with increasing angular momentum of the solid inner core as it grows and decreasing stabilisation properties of the liquid outer core as it shrinks. Is that a ridiculous proposition? After all, the Earth is still a complex set of gyroscopes each with different dynamic properties.

The cyclic part isn't really important other than that there is a strong 100.000 years cycle signal visible which hasn't been explained, (but all players here are cyclic). For the moment we concentrate on the thermodynamics of a cooling Earth core, variable inner core size due to solidification and core mantle friction due to precession differences of the inner core gyroscope and the mantle gyroscope which might or might not prevent complete core solidification or it might lead to loss of spinning energy akin to the mechanisms of Correia et al 2002. Or is that ridiculous?

 

[billiards]

Andre, to the best of my knowledge the inner core has been growing, just that, just growing. (I accept that its spin is not perfectly aligned with the mantle - that was never my issue - so please let's not go back there.) I thought I had made myself perfectly clear earlier; but I will reiterate for your benefit.

I find the notion of an inner core which undergoes cyclical melting and cooling ridiculous. This to me implies a growing and shrinking inner core! (I accept major events such as moon forming impact, could have melted (and shrunk) the inner core somewhat, but such events are not cyclical!)

I feel I must tread carefully here because some of your statements, such as the following, are not obviously incorrect (although I will try to show that this one is - given that by "variable" you clearly seem to be implying "growing and shrinking").

... variable inner core size due to solidification and core mantle friction due to precession differences of the inner core gyroscope and the mantle gyroscope...

Let's have a look at what an expert on this subject has to say: Don Anderson (http://www.gps.caltech.edu/~dla/Commentary-doc2.pdf )

The inner core is subjected to a variety of external stresses involving variations in orbital and rotational parameters, tides, gravitational tugs from the mantle, viscous drag of the outer core and electromagnetic forces. It may also generate internal stresses by thermal and chemical variations, anisotropy and cooling, and respond to these by porous flow, differential rotation, convection, and deformation and creation of material anisotropy...

The conventional explanation of the formation of the solid inner core involves slow cooling and crystallization. Since the melting temperature increases with pressure
the core will solidify from the center outwards.

A growing inner core is needed to power the current dynamo but rapid cooling may have
powered the ancient dynamo (9). The inner core may therefore be much younger than
the Earth. The heterogeneity and anisotropy of the inner core may help constrain its
apparently complex history.

So deformation of the inner core may occur by a variety of mechanisms, however, this does not necessarily mean that it can shrink. If a growing inner core is required to power the Earth's magnetic field, then a shrinking inner core would be detectable in the palaeomagnetic record (I guess it would appear as a drop to 0 intensity). There is no palaeomagnetic evidence to support this, especially at 100,000 yr periodicity!

So we have no evidence that the inner core shrinks, and you have certainly not proposed a viable geophysical mechanism that would allow for the inner core to shrink. The only geophysically plausible way to shrink (melt) the inner core is to either (1) provide a great new source of heat, or (2) release a vast amount of pressure. If I were you I would either give up your wild goose chase, or if you're really convinced you're on to something, take a PhD in deep Earth geophysics, run some calculations, and (if you turn out to be right) get them published in a reputable scientific journal.

 

[Andre]

Thanks Jack, a great post which makes it easy for me to ponder about ..

(1) provide a great new source of heat

(without needing to formulate new theories)

So we have the extemely powerful rotation energy of the complex set of Earth gyroscopes and the different precession tendencys of the various Earth shells. And of course inertia, both thermal and dynamical inertia. So a wild speculation here:

Assuming, just assuming, that the net energy flow of the inner Earth core is negative (meaning that nuclear decay is not the primary heat source), then we should assume (hey, idea only, right?) that the inner core is growing naturally as a result of solidification following the loss of heat. A bigger inner core gets increasingly stubborn about following the precession of the equinoxes tendency of the mantle due to the gain in angular momentum. As a direct result, lagging that precession, the oblique spinning inner core generates a lot of friction in the liquid outer core, converting spinning energy to heat. As a result of the increasing heat the inner core melts partially again, decreasing the angular momentum again and increasing the magnetic/dynamic ability of the outer core to stabilize the inner core spin axis. So as soon as the cyclic deviation in precession between spin axis disaligment is completed, both core and mantle spin axes line up again and remain aligned for a while because of the shrunken size of the inner core, obeying to the precession logic of the mantle again. But then the cooling kicks in again, causing a next cycle. That's why the 100,000 years cycle could be explained but I'm the first to concede that we need a lot more to sustain that.