solid Earth core

[bored_teen]

i've always been taught that the Earth's core has 2 parts: an outer and inner. the outer is supposed to be liquid, but the inner is solid. the way i've learned it is that the inner core is so hot, it is a solid instead of a liquid. but my understanding of thermodynamics contradicts this. how can a liquid become solid by heating? if this is so, would zero Kelvin be liquid instead of solid? or something even colder than zero Kelvin?

[Cap'n Refsmmat]

The reason the inner core would be solid is because of the immense pressure (the entire Earth) pressing on it. That makes it a solid regardless of its incredibly high temperature. (Although the solidity of the core is not firmly established -- it's hard to gather evidence about the center of the planet.)

[bored_teen]

i see. interesting. but then why is the outer core still liquid? is the point at which the core becomes solid also the point at which the pressure is great enough to solidify?

[insane_alien]

is the point at which the core becomes solid also the point at which the pressure is great enough to solidify?

 

bingo, you hit the nail on the head there. the outer core doesn't have enough pressure on it to solidify, so it can remain fluid. but the inner core does so it crystalises.

 

how can a liquid become solid by heating?

 

this is off topic but it may interest you to know that there are some mixture that are liquid at room temperature but become solid upon heating before turning liquid again. this requires some interesting solubility characteristics.

[Klaynos]

A bit off topic too, but He3 I think it is when you cool it down at the right pressure it can go liquid -> gas -> liquid -> superfluid over quite a small temp range...

[bored_teen]

cool. seeing as the original question has been answered, i don't think anyone will mind this thread being derailed, especially by the OP.

 

my new question is: what's a superfluid? why is it "super"? is it another state of matter, along with solid, liquid, gas, and plasma?

[insane_alien]

a frictionless fluid. its called a super fluid because it behaves more like a perfect fluid than normal fluids like water.

[Klaynos]

cool. seeing as the original question has been answered, i don't think anyone will mind this thread being derailed, especially by the OP.

 

my new question is: what's a superfluid? why is it "super"? is it another state of matter, along with solid, liquid, gas, and plasma?

 

Yep it's another state of matter, there are infact loads of them!

 

A superfluid is a fluid that has no viscossity. So it just flows through tiny tiny holes as if the whole was massive...

 

They've got other properties as well like really high heat conductivity... You can make them do things like create fountains several meters high by just making a small hole in something of the right shape...

[bored_teen]

Yep it's another state of matter, there are infact loads of them!

 

A superfluid is a fluid that has no viscossity. So it just flows through tiny tiny holes as if the whole was massive...

 

They've got other properties as well like really high heat conductivity... You can make them do things like create fountains several meters high by just making a small hole in something of the right shape...

 

that's pretty cool. so, for all intents and purposes, it can go through stuff? do you have a link with all the different known states of matter i could check out?

Edited June 12, 2008 by bored_teen

[Edtharan]

The way I understand it is:

 

As the liquid iron core cools, it becomes more dense, this causes it to move towards the centre.

 

Now at the location where the iron is cool enough to crystallise out as a solid, it releases some of that heat energy to do so. This warms up the liquid iron just outside of that (as the heat has nowhere else to go), which becomes less dense and is pushed outwards by the incoming cooler iron.

 

This sets up a convection current, and any motion of a conductive liquid (and liquid iron metal is conductive) in the presence of a small initial magnetic field will act as a dynamo and amplify that initial magnetic field. This is the source of the Earth's magnetic field.

 

what's a superfluid? why is it "super"?

Because it comes from the planet Krypton .

 

Seriously though, what Klaynos said is right. It is a fluid without friction. It is caused by the fluid being so cold that certain quantum mechanical effects that are usually swamped by the vibrations of all the atoms in the fluid (heat is really just atoms vibrating).

[bored_teen]

The way I understand it is:

 

As the liquid iron core cools, it becomes more dense, this causes it to move towards the centre.

 

Now at the location where the iron is cool enough to crystallise out as a solid, it releases some of that heat energy to do so. This warms up the liquid iron just outside of that (as the heat has nowhere else to go), which becomes less dense and is pushed outwards by the incoming cooler iron.

 

This sets up a convection current, and any motion of a conductive liquid (and liquid iron metal is conductive) in the presence of a small initial magnetic field will act as a dynamo and amplify that initial magnetic field. This is the source of the Earth's magnetic field.

 

wait, so the inner core is cooler than the outer core?

[D H]

No. That is incorrect. The inner core is hotter, but under considerably more pressure. The melting/freezing point of iron increases as the pressure increases. Squeeze molten iron enough and it will become solid.

[Klaynos]

that's pretty cool. so, for all intents and purposes, it can go through stuff? do you have a link with all the different known states of matter i could check out?

 

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

[bored_teen]

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

 

thanks!