What is the mechanism behind the heating of the Earth's core?

[carl fischbach]

Heating of the Earth's core must have a logical
solution, which led me to this idea, the work
done by gravity on vibrating molecules throughout
the Earth moves the surface heat of the earth
towards the Earth's core,amplifing it as it moves
to the Earth's center.This is backed up by the
fact that, if you had molecules bonded together in
a long string vibrating back and forth, and kept
one end vibrating at a minimum velocity and applied gravity
along the direction of the string
towards the other end,you would find that end
opposite to the one maintianed at minimum velocity
would be vibrating at a greater velocity than
the minimum velocity end.Could it be possible that
the Earth's core is heated this way?

 

[Jonathan]

I think no. The string idea may make sense, but I didn't understand it. I think no because if hot air balloons rise because they are less dense, then so too would hot molecules. Therefore one would have to do work to make the hot molecules move generally toward the center. I've heard two theories that I'm partial to: massive amounts of radioactivity at the core, which makes sense considering how dense radioactive stuff is. The other is a neo-aether theory where matter is considered to be 4d vorticies in this aether, and apparently when the aether gets to the center of the vortex, it pops out of existence. But because the aether is, well, etherial, you never run out of it. It's really kind of like a spirital essence. BTW, I've heard of the Michaelson-Morley experiment, but I like this aether theory though because it explains the null result: If aether is flowing into all massive bodies, then gravity is a push force resulting from this aether 'wind' and this wind blows normal to the surface of a body. (Radially inwards in the case of spherical bodies.) If the MM experiment was conducted vertically here on earth, one could prove this one way or another. But I digress, so by some method I don't understand, this influx of aether is supposed to cause the interior heating of all bodies, but is only noticable on large scales, just like gravity, so one really doesn't see it in everyday life.

 

[russ_watters]

Its important to understand that the Earth isn't gainin/generating heat. All of the heat in the core is residual - it was created in the formation of the Earth from gravity.

 

[chroot]

Actually, most the heat in the interior of the Earth is due to naturally-occuring radioactivite isotopes.

- Warren

 

[russ_watters]

Originally posted by chroot
Actually, most the heat in the interior of the Earth is due to naturally-occuring radioactivite isotopes.

- Warren

You sure? Thats a whole ton of radioactivity.

 

[Jonathan]

Look's like we have two experts disagreeing on basic facts. You guys, the fact is that no one really knows for sure the source of the Earth's core heat (or if it is increasing/decreasing/steady) or the exact amount of that that is attributable to each different possibility (if more than one is occurring). The radioactivity one makes sense though, of all the radioactive stuff on Earth, most of it would fall to the core if it was liquidish and submersed in liquidish stuff because of its high density. This is esp. true in this case where most of the Earth's mass is liquidish (I think). Yes, I know, liquidish is not a word!

 

[Phobos]

Originally posted by Jonathan
Yes, I know, liquidish is not a word!

I like it...feel free to use it in this forum!

This topic, however, must go to the Other Sciences forum.

p.s. Welcome to PF, Carl!

 

[Janus]

Originally posted by Jonathan
Look's like we have two experts disagreeing on basic facts. You guys, the fact is that no one really knows for sure the source of the Earth's core heat (or if it is increasing/decreasing/steady) or the exact amount of that that is attributable to each different possibility (if more than one is occurring). The radioactivity one makes sense though, of all the radioactive stuff on Earth, most of it would fall to the core if it was liquidish and submersed in liquidish stuff because of its high density. This is esp. true in this case where most of the Earth's mass is liquidish (I think). Yes, I know, liquidish is not a word!

Actually, the term you mean is plastic

I would say that both are correct, it is a combination of residual heat and radioactive decay. The radioactive decay acting to slow the cooling.

 

[russ_watters]

Originally posted by Jonathan
Look's like we have two experts disagreeing on basic facts.

No need to call me an expert here - this isn't my field.

It just seems to me to be unnecessary to assume the core is highly radioactive. And that it would make a planet like Jupiter considerably cooler since it must contain far less radioactive elements (by mass percentage), yet Jupiter gives off a lot of heat.

Gravitational collapse is what initially heats stars and gas giants and that's not all that difficult to model. It doesn't seem reasonable to me to think there must be another source for the heat in the earth.

 

[Jonathan]

I thought I heard at some point that they modeled those type of things and that the heat coming from the core was anomalous. IMO, russ should have the benefit of the doubt in expertise and for all intents and purposes he's an expert on most things, unless of course he humbly denies it.

 

[Andre]

So where dooes the heat come from?

So far we have seen three ideas I think.

Residual compression heat from the original formation of the Earth. However I have read somewhere that it would have taken only a few (2-3) billion years for the Earth to cool, when looking at the normal physical relationships.

Another idea is the http://geology.about.com/library/weekly/aa072102a.htm but nuclear engineers who know how critical parameters of nuclear reactors are, usually strongly oppose this idea. Although random natural radioactive decay of elements would generate some heat througout the inner earth, slowing down the cooling process, it is doubtfull if that could amount to retain such a tremendous heat.

Then there seem to be some crackpot view with vibrations and vortices. Can't really work with that.

Now, what generates heat in nature other than chemical and nuclear processes? Compression and friction for instance. Now, the mentioned causes seem not sufficient to retain so much heat. We may have to add another unaddressed heat source: friction!

Unthinkable? Well, I do have this hypothesis.

Why is Venus so extreme hot (720 degrees Kelvin) ? greenhouse runaway? Come on.

 

[FZ+]

Why is Venus so extreme hot (720 degrees Kelvin) ? greenhouse runaway? Come on.

Combination of that and rampant volcanism, AFAIK. The greenhouse runaway may also be a result of volcanism. What little data we have show crustal plateaus etc that suggest a very active geology.

I really don't think tidal friction is truly a significant factor in this. There is certainly no evidence for that being a significant factor, at least as far as I am aware of. If we are working on the idea of this volcanism being the effect of the tidal friction, then this is disputed by heavy volcanism further out in the solar system. Eg. mars.

 

[Andre]

OK, let's explore this some more, with the consent of the thread owner of course. So Carl, if you don't mind.

We were talking about Earth interior heat. Heat is energy. There was some law with consevation of energy. We could have a look at Earths total energy. The main components of Earths energy could be it's turning energy and it's interior heat.

Now, let's look at venus. As Venus is supposed to be Earths twin planet with most parameters within the same rough order of magnitude, the energy equation is quite different. Venus has much more heat but no rotation, actually a little backwards rotation.

So what does this suggest. All Venus previous rotation energy may have been converted to heat. Consequently Earth rotation energy may also be converting to heat gradually, but only noticaeble witin the interior so far.

 

[russ_watters]

The problem with modeling heat loss for a planet is that a couple of clouds is all it takes to throw the end result way off.

 

[LURCH]

Originally posted by russ_watters
No need to call me an expert here - this isn't my field.

It just seems to me to be unnecessary to assume the core is highly radioactive. And that it would make a planet like Jupiter considerably cooler since it must contain far less radioactive elements (by mass percentage), yet Jupiter gives off a lot of heat.

Gravitational collapse is what initially heats stars and gas giants and that's not all that difficult to model. It doesn't seem reasonable to me to think there must be another source for the heat in the earth.

But Jupiter is a much larger sphere, and therefore has less surface area for its mass. It would be expected to have a higher initial temperature, and to cool more slowly.

 

[Nereid]

Quantification anyone?

Re the Earth:
1) the vertical heat flow through the upper parts of the crust is easily measured
2) the energy generated by radioactive decay (⁴⁰K, U, Th, etc) is well known; within the Earth it all gets turned into heat
3) make some reasonable assumptions about which elements moved preferentially to the core, and which to the crust
4) build your model, press the GO button, and ...

Re Venus:
1) solar insolation is well known
2) atmospheric composition is (now) well known
3) {like 4) above}

Re Jupiter:
A few more complications as the composition of the Jovian core isn't well understood. However, the major new factor is the gravitational potential energy converted to heat as the planet differentiates; esp as He settles to the core (and H rises).

 

[Chemicalsuperfreak]

I'll admit that it does seem weird that the interior of the Earth is heated by radiation. But I'm pretty sure it's quite well accepted. I don't remember numbers, but I think uranium constitutes a much greater proportion of the Earth's composition than one would naturally think. Furthermore, I don't think it would take a huge amount of radiation, since there is so much insulation to keep things hot.

I once read an article, can't remember journal or specifics, about this weird uranium rich formation under Africa I think it was. Apparently it was acting as some large, very slow, self sustaining breeder reactor. Like I said, I don't remember the details. Apparently they used the data to calibrate uranium-thorium dating, and turns out the method is quite accurate.

 

[carl fischbach]

This is an interesting discussion I've started
here.I'm not saying that the energy is created out
of thin air,what I am saying is that the sun's
energy absorbed on then surface planet is transferred by gravity to the interior of the planet.With a solid planet modeling this is tricky.With a gas giant the model is simple.
Each molecule of a gas giant migrates over it's
entire interior.As it moves towards the center,
from the surface, it gains velocity due to the work done by gravity.As it returns to the surface,
it loses velocity due to work done against gravity,but it also loses energy due to the molecule radiating infrared radiation.This causes
the molecule to return to the surface at a slower
velocity than it left.Now it absorbs more energy from the sun.I could get into this in terms of
collision science but it is a little to technical
for this format.If you take away the sun's heat, the gas giant would freeze solid in a relatively
short period in terms of the geological timeline.
Its the sun's radiation that maintains the gas giant's heat for sure.

 

[Nereid]

carl fischbach: It's the sun's radiation that maintains the gas giant's heat for sure.

Both Jupiter and Saturn emit (mostly in IR) more energy than they receive from the Sun (mostly in the optical), so by your reasoning they are generating energy 'for free'. Much more likely that it's due to the fractionation of helium and neon, energy left over the initial collapse, and continued contraction.

carl fischbach: Each molecule of a gas giant migrates over its entire interior

This would only be the case if convection were the mode of heat transport throughout the entire planet (and there were no solid core).
[edit: 'hot' molecules won't sink anyway; in a convective flow, they rise]
However, IIRC, there is a solid core - metallic hydrogen? - and the atmosphere is not fully convective. Perhaps a good tutorial on planetary physics would help?

Chemicalsuperfreak: I once read an article, can't remember journal or specifics, about this weird uranium rich formation under Africa I think it was. Apparently it was acting as some large, very slow, self sustaining breeder reactor. Like I said, I don't remember the details. Apparently they used the data to calibrate uranium-thorium dating, and turns out the method is quite accurate.

You're referring to Oklo, I think. It was a natural nuclear reactor (stopped a long time ago) and it has enabled a few strong constraints to be placed on the time variability of important physical constants. More info here:
http://www.ans.org/pi/np/oklo/

However, normal radioactive decay generates heat, and it's that which is the most important source of heat for the Earth's interior.

 

[Jonathan]

Carl, I've already determined and said that hot molecules sinking to the core and coming back cool defies Archimedes' principle and the laws of thermodynamics, because, in Jupider for example, one would have to have a huge Maxwellian demon living there to cause this self organization of temperature differential reverse to bouyancy.

 

[isaacsgf]

There may be a contribution of heat from the Earth's crustal flexing from the variation in the magnitude of the gravitational attraction of the moon and sun and the rotation dynamics of each of the bodies. How about heat generation from the interaction of the Earth's magnetic field and that of the sun?

Does anyone have a good reference that provides the best guesses at the proportion of longlived radioisotopes present in the proto-solar cloud from which the solar system formed and the rate of heat conduction and convection through some (bogus average)of the interior constituents of the earth? Have the several joules/second of radiant energy provided by the sun been arriving at a somewhat constant rate over the last 5 billion years. Let's not ignore the energy partitioning at the molecular/atom level extant at the high end of the gaussian distribution of the energy per atom at the Earth's center and how that may contribute to fusion and the heat so generated. [zz)]

 

[Andre]

Wow, Isaac, Welcome and do you have a translation for all that?

Personally I think we should look at Venus to understand something about the heating of planets.

 

[sage]

what's wrong with radioactive decay and very good insulation(coupled with high pressure at the centre) as the cause of the heat at the interior of the earth. andre i could not get any new info on venus from the last time we discussed about it. seems we have to wait for a new NASA mission, but then they are obssessed with Mars currently. (oh! i added you on my buddy list. after all we have had some great discussions about some pretty innovative theories).

 

[Andre]

Sage,

I guess that radioactive decay is a basic thruth. There is nothing wrong with that. The question is the magnitude. But one thing seems certain. The decay inherently continues and the generated heat will diminish gradually with its effect on the size of the solid inner core as you have argued somewhere else. Somebody calculated (have to find it back) that the original compression heat of Earth would have been gone for some billiard years by now. Something kept the heat up. Natural radioactivity is one. Internal friction is another.

There is also the thermonuclear core hypothesis, assuming a fission reactor in the core of the Earth. This would yield a multitude of heat compared to natural radioactivity. This is not the same of course and it´s existence is highly debated.

FYI I had some pretty good Venus discussion here.

http://uplink.space.com/showflat.ph...528370&page=2&view=collapsed&sb=5&o=0&fpart=3

 

[russ_watters]

Originally posted by sage
what's wrong with radioactive decay and very good insulation(coupled with high pressure at the centre) as the cause of the heat at the interior of the earth.

I don't like the radioactive decay theory because of radiation and the requried mixture of elements in the earth. Seems like an awful lot of uranium whereas metorites hitting the Earth are mostly iron or stone.

 

[Chemicalsuperfreak]

Originally posted by russ_watters
I don't like the radioactive decay theory because of radiation and the requried mixture of elements in the earth. Seems like an awful lot of uranium whereas metorites hitting the Earth are mostly iron or stone.

Hmm, looks like it's mostly radioactive potassium. I wonder how much modern models agree with Lord Kelvin's.

http://www.nature.com/nsu/030505/030505-5.html

 

[Andre]

I've read the article but I don't get it. The idea is that potassium dissolves very well in ferro sulpheric compounds. Hence the core could be rather right of potassium. and heavy pottassium 40K is radioactive, producing heat, when decaying.

Most be hard to get the numbers right. The half-time of (rare) 40K is 1250 million years. That means that the radioactivity is very very low. Secondly, 40K decays to 40Ca and 40Ar, meaning that the mass loss that transfers to energy can't be very big. Hard to image that this minute radioactivity can amount to 0,4 - 0,8 Tera watt (per second ?) within the Earth core.

Anybody familiar with these calculations?

 

[Andre]

OK I found myself an old enveloppe and after some scrabbling I estimate the about of potassium required to be in the range 0f 10% of the volume of the Earth core to 9 times the Earth core. But I'm not sure of the data.

Realistic?

 

[Bystander]

Originally posted by Andre
I've read the article but I don't get it. The idea is that potassium dissolves very well in ferro sulpheric compounds. Hence the core could be rather right of potassium. and heavy pottassium 40K is radioactive, producing heat, when decaying.

Most be hard to get the numbers right. The half-time of (rare) 40K is 1250 million years. That means that the radioactivity is very very low.

No. It means the decay constant is small, 1.2x10^-17s^-1.

Secondly, 40K decays to 40Ca and 40Ar, meaning that the mass loss that transfers to energy can't be very big.

1.4-1.5 Mev --- not huge, not trivial.

Hard to image that this minute radioactivity can amount to 0,4 - 0,8 Tera watt (per second ?) within the Earth core.

It is NOT necessary to "imagine" --- do the arithmetic: mass of Earth times abundance of potassium times abundance of K⁴⁰ divided by relative atomic mass times Avogadro's number times decay constant times decay energy equals power output. You should come up with 3-10 x 10¹⁵W working with cosmic or crustal abundance figures for potassium --- that's 100 - 300 times the crustal heat flow from Fairbridge, 65 mW/m². One of the problems that has to be dealt with in accretion models is the LOSS of volatiles during the process.

Adjectival quantifications can be misleading --- doing the actual arithmetic with numbers that have been available for years is very much the preferred approach.

 

[Smart Guy]

Core Heat hmmmmmm. let's see.

Friction&Pressure.Duh huh. Now let's go deeper. Stop looking at the core and look at the mantle. The core is hot always been hot. The reason it won't cool is because it is surrounded by the perfect insulator(ie.molten rock). Then on top of that we have our atmosphere.
Unlike the larger gas planets (which are larger due to expansion)Our planets crust cooled and trapped heat inside. How is heat still being generated after millions of years? Well I of course have a theory. Because till we go there. To be Continued...

 

[Andre]

Smart Guy:

The reason it won't cool is because it is surrounded by the perfect insulator(ie.molten rock).

Well nobody has been there to check it but the current model would be this:
http://www.corvus.com/planets/earth.htm

The Earth's interior is differentiated. Because the density of the entire Earth is 5.52 g/cm(3), and the crust is much less dense, the interior is made of very heavy elements. It is divided into four areas.

The crust is very thin relative to the radius of the Earth, only 35-60 Km deep. In fact, with respect to the size of the Earth, it is proportionally thinner than the skin on an apple.
The mantle is a layer of dense rock, which is very hot, and under a lot of pressure. The heat and pressure make the rock plastic, or malleable. The mantle is denser than the crust, which floats on it. As the mantle moves, the crust floating on it also moves, causing earthquakes.
The core has two regions, a liquid core and a solid core. The interior of the planet can be explored by monitoring shock waves from earthquakes. As the surface crust is dislocated, the shock of the motion spreads through the Earth. There are two types of waves that result. S-waves are shaking waves, like the shaking of jello. P-waves are pressure waves like sound waves. P-waves will travel through all materials, but S-waves only travel through solids. When an earthquake strikes one part of the Earth, S and P waves are felt nearby, but P-waves are also felt on the other side of the Earth. Therefore, the center of the Earth must be liquid. This liquid core is made of molten iron and nickel and has a density of about 14 g/cm(3), compared to 3.0 g/cm(3) for the crust and 4.4 g/cm(3) for the mantle. In the inner core, the pressure is so great that the iron and nickel become solid again.

If you read carefully, you may have have missed "molted rock". plastic rocks ok, Molten iron ok, but that's not really renounced for being a perfect insolator.

 

[Chemicalsuperfreak]

Originally posted by Andre
Smart Guy:


Well nobody has been there to check it but the current model would be this:
http://www.corvus.com/planets/earth.htm



If you read carefully, you may have have missed "molted rock". plastic rocks ok, Molten iron ok, but that's not really renounced for being a perfect insolator.

I don't know how old that quote is, but it looks pretty outdated/incorrect. P waves are not felt on the exact opposite of the earth. The are blocked which is why it is believed the Earth's core is solid.

 

[Andre]

OK Perhaps more a little less correct use of language, or did somebody change the physical laws lately?

http://www.seismo.unr.edu/ftp/pub/louie/class/100/interior.html
http://www.gcsescience.com/pwav54.htm
http://www.calstatela.edu/faculty/acolvil/interior.html

 

[Smart Guy]

Thank but No.

That was a cute website a lot of valuable information for my sons science fair project in which he won first place this past summer, but the skin of an apple is thick enough to hold in water just as the crust is thick enough to hold in heat. The only relevance that has is the crust is thin enough to let excess gas and pressure be released in very small quanities. The core ,solid minerals; denser rock and minerals sink. Except water. Ice floats. The mantle, molten rock or minerals (since this is a science forum). The heat, already there kept steady by the constant movement of the Earth's crust which is miles and miles deep. The crust kept cool an in a solid state by the atmosphere of course. The Earth is heated internally by the residual heat circulating, and since I said the core is solid minerals or simi-solid then the majority of the heat would be in the mantle.

Prove me wrong

 

[Andre]

Prove me wrong

That's not fair, Smart guy, He, who proposes an alternative theory or hypothesis, not in line with the scholar ideas, has the onus of proof, That's rule nr. 1A(1) in science.

How about if I stated that the Earth was hollow and prove me wrong

This is the scholar idea:

http://www.gcsescience.com/rk3.htm
http://pubs.usgs.gov/publications/text/inside.html

Below the crust is the mantle, a dense, hot layer of semi-solid rock approximately 2,900 km thick. The mantle, which contains more iron, magnesium, and calcium than the crust, is hotter and denser because temperature and pressure inside the Earth increase with depth. As a comparison, the mantle might be thought of as the white of a boiled egg. At the center of the Earth lies the core, which is nearly twice as dense as the mantle because its composition is metallic (iron-nickel alloy) rather than stony. Unlike the yolk of an egg, however, the Earth's core is actually made up of two distinct parts: a 2,200 km-thick liquid outer core and a 1,250 km-thick solid inner core. As the Earth rotates, the liquid outer core spins, creating the Earth's magnetic field.

Again, if nobody stealthily changed the physical laws for P-waves and S-waves, the mantle is not fluid but semi solid. For (sound) waves it acts as solid. For plate tectonics, hot spots and mantly plumes with dynamics measured over millions of years it acts a bit more as fluid.