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Why is the inner core of the earth solid?

 
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ramaswam



Joined: 22 Feb 2013
Posts: 1
Location: New Jersey

PostPosted: Fri Feb 22, 2013 1:02 pm    Post subject: Why is the inner core of the earth solid? Reply with quote

We are told that the inner core of the earth is solid because of the tremendous pressures there. However, as you move toward the center of the earth, gravitational force should gradually decrease, until, at the center, it is zero.

So can someone explain why the inner core is solid while the outer core is liquid?
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hepcj
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Joined: 23 Jun 2007
Posts: 125

PostPosted: Fri Feb 22, 2013 11:22 pm    Post subject: Reply with quote

It is a good question. The Earth's core is made of iron because it is very dense. It has a high mass per unit volume. Early on in the formation of the Earth, heat from radioactive materials allowed the temperature of the Earth to increase to such an extent that the materials could flow. This caused the iron to sink toward the centre of the Earth.
While it is true the value of gravity will decrease to zero as you go to the centre of the Earth, the pressure from surrounding material is still transmitted to the centre and is pushing on all sides. The gravitational force is zero because the forces cancel out but the pressure is still there.

So the inner core of the Earth is solid because of the intense pressure. Even though the temperature is high, the pressure raises melting point of iron above the temperature of the Earths core. As the radius increases the pressure reduces so the iron can change state into a liquid and so we have liquid iron around the inner core.
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