Earth's Core

[Ricter]

This question just arose...

Assuming that the Earth's core is hot because of the compression of matter, and assuming for the moment no outside changes like Sol going nova, etc., would this mean that the Earth's core will always be hot?

Thanks.

[StarLab]

I'm not sure, but there are a lot of interesting theories flying around. Some wisecrack (don't know his name) speculated that there is a collection of uranium at the center of the earth. I've been hoping for the last year someone could come out and lay this theory in its grave for good.

it seems for the moment, however, that earth's core would eventually cool. This could be due to any major fluctuation or decrease in earth's magnetic field, there would occur a nuclear or biblical armaggedon some time in the near future, or earth, like the sun, could just grow old.

Remember, as discussed in H.G. Wells' The Time Machine, the earth's rotation will gradually slow down/decrease/get slower, until one day it stops completely. THEN the earth's core may indeed stop spinning (though plants may still be able to exist if the sun is still shining and giving off sunlight).

[Ricter]

Originally posted by StarLab@Apr 30 2004, 04:08 PM
I'm not sure, but there are a lot of interesting theories flying around. Some wisecrack (don't know his name) speculated that there is a collection of uranium at the center of the earth. I've been hoping for the last year someone could come out and lay this theory in its grave for good.

it seems for the moment, however, that earth's core would eventually cool. This could be due to any major fluctuation or decrease in earth's magnetic field, there would occur a nuclear or biblical armaggedon some time in the near future, or earth, like the sun, could just grow old.

Remember, as discussed in H.G. Wells' The Time Machine, the earth's rotation will gradually slow down/decrease/get slower, until one day it stops completely. THEN the earth's core may indeed stop spinning (though plants may still be able to exist if the sun is still shining and giving off sunlight).

Ok, I'm not aware that Earth's magnetic field has an effect on the core temperature. I can't imagine how a nuclear war (that humans can presently wage) could possibly effect the core temperature either.

I have read a bit about the decay of atoms (specifically protons?), but don't know enough about it.

I thought the mass of the Earth was enough to explain most of its core temperature... Shrug.

[Duane]

The core will cool, however the time involved is longer than the life of the sun.

The melting is thought to be the result of the initial formation of the planet (accretion adn impacts) combined with the heat from radioactive elements, including uranium.

[antoniseb]

I had the impression that the Earth's core started hot from the heat of a lot of inelastic collisions as the Earth formed [especially the Mars-sized one that may have created the moon], with some additional heat provided by the decay of some of the shorter lived isotopes that made up the Earth.

I don't know the reason it is still hot but one factor would have to be that two thousand miles of rock would have to have a pretty impressive R-value [as insulation]. Perhaps tidal heating from the moon deforming the earth a little bit is also a factor.

[Tim Thompson]

I don't know how much of the heat energy in the core now is energy left over from the formation of the planet. It could be a substantial fraction. But there is continuous and significant heat energy still being produced, by the decay of radioactive potassium (probably 40K), and by the latent heat of fusion as the liquid outer core condenses onto the solid inner core. But the latter is a slow process, and it is generally accepted that the radioactive potassium heat input is the major source of new heat for the liquid outer core, with a smaller contribution from uranium & thorium. The temperature at the core/mantle boundary is about 3300 Kelvins, and may be as high as 5000 kelvins in the solid inner core.

Pressure can only add heat to a compressible material, where the heat is added by the work done to decrease the volume. Since the Earth's interior is not compressible, the pressure does not add heat. But it does determine the state of the interior for a given temperature. The solid inner core is solid because of the pressure, there would be no solid material at 5000 Kelivins, at the pressure of the Earth's surface, where we are.

As for the magnetic field, it is more a matter of the temperature affecting the field, than the other way around. The magnetic field is likely generated by dynamo action in the convecting liquid outer core, which depends on the combination of pressure & temperature to remain fluid, and to remain convective. Eliminate the convection, and you eliminate the field (which is probably the case for both Venus & Mars, neither of which has plate tectonics, which serves to cool the core and promote convection).

[StarLab]

I think that the question of the activity of earth's core is a very good question to ask, but the answer seems to dictate that the idea the core could stop anyways is far-fetched, since it has been indicated it would stop Waaay after the sun devoured it. Plus, by that time humans would have gone far beyond the bounds of the solar system.

[Greg]

Its too bad we cant just go down there and look. The Russians were trying but got no further than 60? miles before running out of funds to dig deeper intot the crust. Recently somebody proposed an idea for a molten iron encased probe which got some press, but of course was impossible to implement. Guess we will have to rely on seismic data. Are there are any othrt bright ideas for sounding out (probing) what lies beneath?

[antoniseb]

Originally posted by Tim Thompson@May 1 2004, 02:12 AM
...probably the case for both Venus & Mars...

Planet cores are not something I've studied much.

If Venus and the Earth are nearly the same size and composition, and Potassium-40 is our core's major source of heat, why would Venus' core be frozen now and Earth's not?

Is it possible that Venus does have a liquid outer core as Earth does, but that its very slow rotation rate makes its magnetic field very small and amorphous?

[GOURDHEAD]

The earth's core is believed to be largely iron and nickle and that seems to be a safe bet. Is differentiation complete? My guess is that as years go by more and more uranium, thorium, their decay products, and possibly plutonium created from natural causes (alpha capture in the dense environment) are continuing to concentrate near the center of the core and probably sustaining or even increasing the heat content. Conceivably this could lead to a more turbulent convection peak, excessive volcanism, and even the explosion of the planet. Forgive the hype; I'm recruiting adherents for interstellar transportation development.

The characteristics of some asteroids make it easy to believe that they are the remnants of an exploded planet or at least a powerful collision. Do we know or have strong theories as to where these asteroids come from or how they were caused to be?

Has anyone worked out the upper limit of the heat contribution of the moon's gravitational interaction with the earth?

Does potassium have a sufficiently long half-life to be a major contributor after > 5 billion years?

[Greg]

I do not think the Earth's core will "Explode" any time soon. Yes there probably is a significant amount of uranium down there. Just how much is a matter of hot debate. It won't be easy to find out from what I can gather. If there were alot of uranium or plutonium down there, I doubt it is weapons grade material (specific isotopes.) I don't know whether or not it would be concentrated in one area, but it is likely not. I do not see how a significant explosion (detonation) could occur to set off the chain reaction of a fission explosion. I don't forsee terrorists being able to go down there to set one off (that is a joke.) Even if a detonation were possible, I'm sure the resulting explosion would extremely well contained. We might not even feel it at the surface. Our gov't has a penchant of violating arms treaties to test some new nuclear bomb designs below ground. I doubt that they are more than 10 miles below with a whallop in the megatons, yet they barely register on a seismometer.
As far I know, the most widely accepted theory of how the asterooid belt formed is that there wasnt enough material to form any object due to the gravitational effect of Jupiter. A minority opinion is that some body formed there and later broke up, possibly after a large collision. But certainly objcts can be destroyed after they form, but usually the resulting debris gets itself together again into a new body in the same orbit.

[Tim Thompson]

antoniseb If Venus and the Earth are nearly the same size and composition, and Potassium-40 is our core's major source of heat, why would Venus' core be frozen now and Earth's not?

It's not a matter of being frozen, it's a matter of not being convective. If the planet cannot dump heat out through the surface (crust) fast enough, then the temperature gradient in the core won't be steep enough for significant convection. And if the mantle is not hydrated, it won't be able to convect either, because the mantle viscosity will be too high. So Venus just sits there until the mantle builds up enough heat to force it to convect, and the planet experiences "episodic plate tectonics".

But Earth's mantle is well hydrated, has a lower viscosity, and convects more readily. That transfers heat out to the crust, which is then converted to work moving the plates. That steepens the temperature gradient in the mantle & core, allowing for significant convection, and the consequent magnetic field.

GOURDHEAD Does potassium have a sufficiently long half-life to be a major contributor after > 5 billion years?

Its half-life is 12.77 billion years.

GOURDHEAD Has anyone worked out the upper limit of the heat contribution of the moon's gravitational interaction with the earth?

The moon dissipates ~10^12 Watts, most of which goes into mechanical work flexing the oceans & solid crust, probably only ~10% will go into heating the interior. The total heat energy in the Earth is ~3x10^13 Watts, so the lunar flexing input does not look significant.

[TheThorn]

A related interesting discovery:

As Tim pointed out in his first post, the inner core is solid, very hot, and under enormous pressures. I asked in an earlier thread what form iron takes under those conditions. Austenite is the highest temperature crystal structure of iron in every day temps and pressures, and the "grains" in austenite grow through time, so I speculated that in 5 billion years or so, the solid core would have had time for some serious grain growth - huge austenite crystals.

I did a little searching and found the an article called Crystal at the Center of the Earth. It isn't austenite, (it's a hexagonal close packed structure where austenite is a face centered cubic), but it appears that grain growth has gone to it's logical conclusion - one giant 1500 mile diameter crystal. At least, that's what the evidence indicates. The article describes mathematical modelling that leads to that conclusion, but the key piece of evidence is that seismic waves travel through the core at different speeds depending on the direction - faster pole to pole than across the equator - which is what one would expect from one giant crystal (or possibly many crystals all lined up the same direction).

[galaxygirl]

Originally posted by Greg@May 2 2004, 02:09 AM
Are there are any othrt bright ideas for sounding out (probing) what lies beneath?

We could always build a ship out of unobtanium that has a green lazer thing that melts anything in it's way, send it down through the Marianas trench, and hope the explorers dont run into any geodes. :P

But seriously, I agree with you in that it would be helpful to explore the Earths interior, but it would be hard to do with all that heat and pressure.

[Natasha C]

I'm having some difficulties with an assingment for science. Can anyone e-mali me and help me?

What would happen if you pass through the Crust/Mantel boundary?
Is it possible for Geodes to exist in the Core/Mantel boundary?
can you get to the surface of the ocean by riding a magmatic eruption?

PLEASE help me I'm so confused!!

[Guest]

Natasha C,
Oops, i forgot that my e-mail is tazzy05@hotmail.com

[Bobunf]

“Our gov't has a penchant of violating arms treaties to test some new nuclear bomb designs below ground.”

What is your source for this assertion?

Bob