[Jiggerj]

Hi, I've heard that the earth's iron core hasn't melted because of the immense pressure it's under. Doesn't immense pressure cause immense heat?

[D H]

The entire Earth became hotter than the melting point of iron shortly after the Earth formed. The iron core formed after this melt. This differentiation of the Earth resulted in even more warming. The iron core was entirely molten when it first formed. The Earth's core froze (and is freezing) as the Earth cooled. When the solid core first formed is not known. It was perhaps somewhere between four billion years ago (half a billion years after the formation of the liquid core) to only two billion years ago.

[John Cuthber]

" Doesn't immense pressure cause immense heat? "
No.
The bottom of the ocean is generally cold.

[Jiggerj]

D H, on 12 February 2012 - 09:01 AM, said:

The entire Earth became hotter than the melting point of iron shortly after the Earth formed. The iron core formed after this melt. This differentiation of the Earth resulted in even more warming. The iron core was entirely molten when it first formed. The Earth's core froze (and is freezing) as the Earth cooled. When the solid core first formed is not known. It was perhaps somewhere between four billion years ago (half a billion years after the formation of the liquid core) to only two billion years ago.

Googled info:

Iron melts at 2800 °F
Estimates put the temperature of the inner core of the earth at: 9800.6 ºF

[insane_alien]

yep, but pressure changes the melting and boiling points of substances.

I can make ice at 50 centigrade. just requires suitible application of pressure.

[D H]

Jiggerj, on 12 February 2012 - 10:32 AM, said:

Googled info:

Iron melts at 2800 °F
Estimates put the temperature of the inner core of the earth at: 9800.6 ºF

The melting temperature of iron is 2800 °F at one atmosphere of pressure. That does not mean that the melting point is 2800 °F at the center of the Earth. In almost all substances (water is a marked exception), the melting point increases with increased pressure.

[insane_alien]

D H, on 12 February 2012 - 11:08 AM, said:

...(water is a marked exception)...

To a point. When you get to pressures where different crystalline phases of ice can exist the melting point will increase again and it will behave like the majority of substances again.

[Jiggerj]

insane_alien, on 12 February 2012 - 10:56 AM, said:

yep, but pressure changes the melting and boiling points of substances.

I can make ice at 50 centigrade. just requires suitible application of pressure.

I understand that you are saying it's different with water, but please allow me this example:

I'm boiling water in an open pressure cooker on the stove. I place the lid on the pressure cooker and the water boils more rapidly. Are you saying that if I could melt iron in this way, when I put the lid on (creating more pressure) the iron wouldn't boil more rapidly, but would instead return to a solid state?

[Moontanman]

Jiggerj, on 12 February 2012 - 01:28 AM, said:

Hi, I've heard that the earth's iron core hasn't melted because of the immense pressure it's under. Doesn't immense pressure cause immense heat?

Earth's core.

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

Quote

Temperature

The temperature of the inner core can be estimated using experimental and theoretical constraints on the melting temperature of impure iron at the pressure (about 330 GPa) of the inner core boundary, yielding estimates of 5,700 K (5,430 °C; 9,800 °F).[13] The range of pressure in Earth's inner core is about 330 to 360 gigapascals (3,300,000 to 3,600,000 atm),[14] and iron can only be solid at such high temperatures because its melting temperature increases dramatically at these high pressures (see the Clausius–Clapeyron relation).[15]

Quote

Composition

Based on the abundance of chemical elements in the solar system, the theory of planetary formation, and other chemical constraints regarding the remainder of Earth's volume, the inner core is composed primarily of a nickel–iron alloy referred to as Nife: 'Ni' for nickel, and 'Fe' for ferrum or iron.[10] Because the inner core is more dense (12.8 ~ 13.1)g⁄cm³[11] than pure iron or nickel, even under heavy pressures, it's believed that the remaining part of the core is composed of gold, platinum and other siderophile elements in quantity enough to coat Earth's surface for 0.45 m (1.5 feet).[12] The relative abundance of precious metals and other heavy elements respect to Earth's crust is explained with the theory of iron catastrophe, an event which occurred before the first eon during the accretion of early Earth.

Then you have the inner inner core?

http://www.spacedail.../earth-03k.html

Quote

What would we find if we were to dig a hole all the way down to the centre of the Earth? According to high school science books we would discover a liquid iron alloy core and a smaller solid inner core at the center. For ten years, geophysicist J. Marvin Herndon has presented increasingly persuasive evidence that at the very centre of the Earth, within the inner core, there exists a five mile in diameter sphere of uranium which acts as a natural nuclear reactor.

This post has been edited by Moontanman: 12 February 2012 - 08:44 PM

[mississippichem]

Jiggerj, on 12 February 2012 - 07:51 PM, said:

I understand that you are saying it's different with water, but please allow me this example:

I'm boiling water in an open pressure cooker on the stove. I place the lid on the pressure cooker and the water boils more rapidly. Are you saying that if I could melt iron in this way, when I put the lid on (creating more pressure) the iron wouldn't boil more rapidly, but would instead return to a solid state?

Compare their phase diagrams. Be careful though, the axes are flipped between these two diagrams and the pressure units are different but for the purposes of discussion they are the same.

Run your finger along the isobars. An isobar is a line of constant pressure. Do the isobar at 1 atm then find the boiling points for iron an water at 1 atm. Then try it at a higher pressure. Does the boiling point go up or down?


Iron



water

source for water phase diagram

source for iron phase diagram

This post has been edited by mississippichem: 12 February 2012 - 08:47 PM

[insane_alien]

Jiggerj, on 12 February 2012 - 07:51 PM, said:

I understand that you are saying it's different with water, but please allow me this example:

I'm boiling water in an open pressure cooker on the stove. I place the lid on the pressure cooker and the water boils more rapidly. Are you saying that if I could melt iron in this way, when I put the lid on (creating more pressure) the iron wouldn't boil more rapidly, but would instead return to a solid state?

The only reason water appears to boil more rapidly with the lid on is that there is resuced convective heat loss when it is heating to boiling point.

The point of a pressure cooker is to make the water boil at a higher temperature. If the pressure cooker has a setpoint of 1 barg then it will boil at 120 degrees celcius.

you are operating on a false assumption. also, boiling point isn't the same as melting point and introducing this will only create confusion. There isn't a gas state at the core of the earth so lets ignore it.

Right, to iron. Iron isn't like water, ANY pressure increase will increase the melting point, there is not period of melting point reduction. if we apply a little bit of pressure, we get a little effect, if we apply more, we get a bigger one.


Now, it takes a LOT of pressure to get a decent effect. Many thousands and millions of atmospheres. Luckily, 6000km of rock can do that easy.

If we were to look at the core of the earth and chat pressure and temperature against the distance from the center, we would see two lines with different gradients. if we translated the pressure line into the melting point of iron at that pressure then we would still see two lines with different gradients.

they would also cross over at a certain distance from the center. on the side nearest the center, the melting point is ABOVE the actual temperature, at the cross over point we have the boundary between the inner core and outer core. This is where the pressure falls low enough that the melting point of iron will fall below the actual temperature. If we were to keep going out and the earth remain being mainly iron eventually as we near the surface the temperature would fall below the melting point of iron again as there is only so far the melting point can drop.

Iron Phase

Have a look at that link. It is a research paper about this exact subject. It includes a phase diagram of iron relating the melting point to pressure (and a few other crystalline phase changes)

[Jiggerj]

insane_alien, on 12 February 2012 - 08:49 PM, said:

Isobars, pressure (atm), links to complicated equations... Look, if you people keep throwing this scientific mumbo-jumbo at me then I'm going back to religion! From now I want all my answers summed up in three little words: God did it!