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jimmydasaint

What Sort of Solid is the Earth's Core?

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The structure of the Earth can be split into various layers

as follows, shown at the foot of the page.

 

However, it has been suggested that the temperature of the inner core is made of 'an iron-nickel' alloy with the temperature of the Sun's surface.

 

Two questions arise in my mind:

 

1. Why is is still solid at temperatures in excess of the melting point of iron and nickel?

2. If it is indeed a solid, what kind of solid can it possibly be? Is it like the solids we experience at the Earth's surface, or does it have unknown and exciting properties?

 

Earth-crust-cutaway-english.svg

http://en.wikipedia.org/wiki/Inner_core

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its solid because it is under immense pressure. the equivalent of thousands of millions of atmospheres. this changes the melting and boiling points of materials. you don't usually notice this because the pressures you are used to seeing material at are pretty stable at 1 bar.

 

its just a normal solid. just squashed a bit and very hot.

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You have to keep in mind that the melting temperature of a substance is dependent on factors such as pressure. At the core of the Earth, I can only imagine that there is a fairly significant amount of pressure against the very hot ball of metal.

 

As for its properties - I have no idea. I'm not well versed in the theory of what ever topic the centre of the Earth would fall under.

 

_____________________________________________________________________________________________

 

Ahhh, beaten to the punch

Edited by gonelli
merge multiple posts

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Is it proven to be a solid with 'solid' arguments or are these speculations? Can we recreate the conditions on the surface and still have a solid?

Thanks for the responses above.

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Most of what we know about the core is via extensive analysis of seismic waves. We know for sure it's solid, how dense it is, how it moves, etc. AFAIK stuff like the actual composition, temperature, etc., are educated guesses based on the seismic data, as well.

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Thank you for that Sisyphus. So these are educated guesses. I take it that the idea of a nickel-iron alloy is also an educated guess then?

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Guesses with varying degrees of certainty. The outer core is very probably nickel-iron, based on its density, seismic characteristics, and the fact that nickel-iron is very common in our solar system, but you couldn't say it's actually proven. I also don't know any of the details of the actual calculations they use to determine this.

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no they core is not degenerate matter, the pressures are nowhere near great enough. even the core of the sun is not degenerate matter.

 

as for the composition stuff, the educated guess has underwent a few experiments at a lab scale by sending seismic(which are really just sound waves in a solid) through various materials and seeing which behaves most like the core of the earth.

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To the original poster: What kind of unknown and exciting properties would you think might be possible? I would speculate that even though the core is probably a solid, it might exhibit some kind of "flow" that would permit it to move similar to liquids. But this is pure speculation on my part.

 

If only we could send a probe down there to take measurements and retrieve a sample for us. Of course, it would need to be made from unobtainium: http://en.wikipedia.org/wiki/Unobtainium

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it just occurred to me that the total angular momentum of the earth should be accurately known from its precession rate. that should give some idea of the mass distribution within the earth. (as long as the core isnt some kind of supersolid or something)

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To the original poster: What kind of unknown and exciting properties would you think might be possible? I would speculate that even though the core is probably a solid, it might exhibit some kind of "flow" that would permit it to move similar to liquids. But this is pure speculation on my part.

 

Sh3lock, it has been apparently suggested that fission reactions occur in the inner core to release energy. This is what made me wonder about the nature of the solids in the inner core. They are, perhaps, not the iron and nickel we are used to, on the crust of the Earth.

 

Thank you to all those who posted here. To summarise, the nature of the inside of the Earth and the composition of the core are educated guesses and I will go along with what has been said by people far more knowledgeable than me.

 

However, reading the wiki confuses me. The Outer, liquid core experiences huge pressures, similar to those experienced by the core, yet remains a liquid. This is confusing to me. Also, where does the heat come from for the inner core? Partially from the sun? Or from fission reactions in the core?

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jimmy, fission reactions are rare in the core. it is nuclear deacy(alpha and beta decay)

 

and the outer core is liquid because there is less pressure on it. it also likely has a slightly different composition.

 

the heat itself mainly comes from the formation of earth though. gravitational collapse is pretty good at making heat. just look at all the fireballs made by stuff falling to earth. now imagine a whole earth mass of that over a few million years. not surpirising its still pretty toasty.

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Is it proven to be a solid with 'solid' arguments or are these speculations?

First off, you are being too strict here. Scientific theories are not proven to be true and in general cannot be proved.

 

We cannot (yet) send a probe down to the center of the Earth to tell us exactly what is going on down there. The best we can do is infer what is going on. This includes seismograph readings, high pressure / high temperature experiments, and dynamic models of the Earth.

 

The pressure inside the Earth rises with depth. It eventually starts flattening, but this flattening occurs inside the inner core. The pressure at the inner core / outer core boundary is still rising with increased depth. The temperature is rising also, but not as sharply as the pressure.

 

Finally, the melting curve for iron is anything but a flat line. At the kinds of pressure experienced deep within the Earth the melting curve has a marked slope. If you increase the pressure on a blob of molten iron enough it will solidify. By way of analogy, think of a disposable lighter. You can see the contents as liquid because the contents are under pressure. At ordinary pressure, that liquid would be a gas.

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is the iron in the inner core degenerate?
then why do they say that jupiter is mostly metallic hydrogen?
now I get it. you are thinking that degenerate matter means neutron star material. white dwarfs are also degenerate matter. so is metallic hydrogen

 

In the sense that the distinguishing characteristic of a metal is that the valence electrons form a degenerate Fermi cloud, any metal qualifies as degenerate matter. In the sense that the distinguishing characteristic of degenerate matter is that the "dominant contribution to its pressure rises from the Pauli exclusion principle", no. The density of at the center of the Earth is about 13 grams/cc. For pure iron, this corresponds to iron atoms separated by an average of 192 picometers. The ionic radius of iron varies between 25 and 78 picometers (+6 ionization state to +2 high spin ionization state). The dominant contribution to pressure is still good old electrostatic repulsion.

 

Metallic hydrogen is a different beast. Strip off the one electron from a hydrogen atom and all that is left is the very tiny nucleus.

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Actually in the case of Jupiter the metalic hydrogen covers a inner core of metal and rock possibly several times the mass of the earth. And some do indeed think there is nuclear fission going on in the very inner most part of the earths core....

 

http://www.spacedaily.com/news/earth-03k.html

 

 

 

Of course there is always the outer most part of the inner most part of the outer inner core.....

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The heat is generated by the decay of U, Th and K inside the core, as well as primordial heat remaining from the "Heavy Bombardment" during the early(4550ma - 4000ma) formation of the earth.

 

As for the Fe,Ni composition of the core, this was deduced by seismicity and dating of iron meteorites, which are all the same age - 4550ma.

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at somepoint could you get your lighter fluid to solidify under pressure?

 

Yes, most definitely!

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I just saw the film called The Core for the first time last week. Apart from being unintentionally hilarious as they dived into the depths of the Earth to kick start the core, it was actually quite exciting. If only we could do this and send our most photogenic scientists to the edges of the outer core... :)

 

For those who want to know more:

 

For reasons unknown, the earth's inner core has stopped rotating, causing the planet's electromagnetic field to rapidly deteriorate. Instantly, life around the globe begins to change dramatically. In Boston, 32 people with pacemakers, all within a 10-block radius, suddenly drop dead. In San Francisco, the Golden Gate Bridge collapses, sending hundreds of people plunging to their deaths. In London's Trafalgar Square, flocks of pigeons lose their ability to navigate, flying into panicked crowds, slamming into windshields and causing drivers to lose control of their cars. And in Rome, as thousands of tourists watch helplessly, an electrical superstorm reduces the ancient Roman Colosseum to rubble. Scrambling to resolve the crisis, government and military officials call upon geophysicist Dr. Josh Keyes and a team of the world's most gifted scientists to travel into the earth's core in a subterranean craft piloted by "terranauts" Major Rebecca "Beck" Childs and Commander Robert Iverson. Their mission: Detonate a nuclear device that will reactivate the core and save the world from sure destruction

http://www.imdb.com/title/tt0298814/plotsummary

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that was a very silly film. i don't think it tells us anything useful about the core of the earth except that you need to go down to get to it.

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