Why inner core is solid and outer core is liquid

Q: Why is the outer core is liquid?

Although having a composition similar to Earths solid inner core, the outer core remains liquid as there is not enough pressure to keep it in a solid state.

Q: Why is inner core liquid?

So the Earths core is liquid because its hot enough to melt iron, but only in places where the pressure is low enough. As the Earth continues to age and cool, more and more of the core becomes solid, and when it does, the Earth shrinks a little bit!

Why is the Earth's -inner core a solid and the outer core a liquid?

Question Date: 2013-01-19

Answer 1:

Earth´s inner core and outer core are both made of an iron-nickel alloy. The state of matter (solid, liquid or gas) of a given material depends on its temperature and pressure. Most materials, including iron and nickel, change from liquid to solid at lower temperatures and/or higher pressures. It´s easy to understand going from a solid to a liquid at higher temperatures because we are all familiar with ice melting on a warm day. Why do materials change from liquid to solid at higher pressure? For almost all materials (except water), atoms are packed closer together in the solid state than in the liquid state. So when you squeeze the atoms together with high pressure the material changes from liquid to solid.

Índice Show

Under the tremendous pressure and at the incredible temperatures of the Earth’s deep interior, there’s a thick layer of liquid: our outer core. But why is it so?
Why is the outer core is liquid?
Why is inner core liquid?
Why is the inner core solid and the outer core liquid quizlet?

As you go deeper in the Earth both temperature and pressure increases. Although the inner core is very hot, it is solid because it is experiencing very high pressure. The pressure in the outer core is not high enough to make it solid.

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Ethan Siegel

Jan 17, 2014

8 min read

Under the tremendous pressure and at the incredible temperatures of the Earth’s deep interior, there’s a thick layer of liquid: our outer core. But why is it so?

“If you ever drop your keys into a river of molten lava, let ‘em go, because, man, they’re gone.” -Jack Handey

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The Earth's inner core is solid because despite the enormous temperature in this region, there is also enormous pressure there, which in turn raises the melting point of iron and nickel to a value above the Earth's core temperature.

Now as we move out from the solid inner core, temperature drops, and pressure also decreases. Obviously because the inner core is solid but the outer core is liquid, we must conclude that the drop in temperature vs the drop in pressure must be lower than the gradient of 16 degrees/GPa shown in the diagram below (link to source), given that at the outer-core temperature has exceeded the melting point of iron/nickel, which is a function of pressure.

In other words, the drop in pressure must be quite significant compared to the drop in temperature as radius increases from the core.

So how is it that pressure drops off fast enough relative to temperature to give rise to the liquid outer-core. A good answer will explain how temperature drops off with radius and how pressure drops off with radius and how these compare to give rise to the liquid outer-core.

asked Apr 24, 2014 at 16:42

KenshinKenshin

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First, you need a phase diagram that goes to higher pressure. The pressure at the inner/outer core boundary is over 300 GPa. The one in the question would only get us into the mantle:

(link to source)

A typical temperature and pressure at the outermost part of the core would be 3750K and 135GPa, which is in the liquid region of the phase diagram.

For more data on pressure and temperature as a function of depth see this University of Arizona source. All appropriate credit to Marcus Origlieri.

David Hammen

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answered Apr 24, 2014 at 17:24

DavePhDDavePhD

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The pressure gradient is given by hydrostatic equilibrium. In a solid, this may not be exactly true, but creep will make it so. Let $p$ be the local pressure, $g$ be the local acceleration of gravity and $\rho$ the local density. Imagine a small element of volume with area $A$ horizontal and height $\Delta h$. Its mass is $\rho A \Delta h$ and it is attracted downward by force $g\rho \Delta h$ This has to be balanced by the pressure difference between the top and bottom, so $\frac {dp}{dh}=g\rho$. $g$ can be determined (assuming spherical symmetry) by just counting the total mass at smaller radii.

answered Apr 24, 2014 at 17:23

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Just to add to Dave's answer, the above phase diagrams give the illusion of high precision. In fact, in addition to the temperature distribution, we are not even entirely sure how many sub-solidus phases there are. See for example, Ahrens et al: http://web.gps.caltech.edu/~sue/TJA_LindhurstLabWebsite/ListPublications/Papers_pdf/Seismo_2069.pdf Moreover I was rightly corrected, in a previous answer, when I asserted that the core composition is Ni-Fe with a large sulphur impurity. In fact, although I was probably correct, there is plenty of scope for S2, Ni and other heavy metals, H2, OH-, and other impurities in the core, at unknown concentrations, most of which can create a eutectic depression of the solidus line - that is, shifting the liquid-solid boundary down-temperature.

answered Oct 29, 2015 at 8:49

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Though both the inner and outer core are made of the same material, the melting point of inner core is increased due to the increased pressure, so the inner core is in a solid state and outer is a liquid .

Pont

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answered Oct 29, 2015 at 6:27

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Why is the outer core is liquid?

Although having a composition similar to Earth's solid inner core, the outer core remains liquid as there is not enough pressure to keep it in a solid state.

Why is inner core liquid?

So the Earth's core is liquid because it's hot enough to melt iron, but only in places where the pressure is low enough. As the Earth continues to age and cool, more and more of the core becomes solid, and when it does, the Earth shrinks a little bit!

Why is the inner core solid and the outer core liquid quizlet?

Inner core - High pressure from the other layers at the Earth center makes the inner core solid. Outer core - It is liquid because the temperature is high and there is not enough pressure to make it solid.