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Difficulty: MediumEarth's Interior and Plate Tectonics

Although temperatures in Earth's inner core exceed 5,000 °C, which is well above the surface melting point of iron, the inner core remains solid. Which of the following factors is primarily responsible for keeping the inner core in a solid state?

  1. A
    A high concentration of lightweight silicate minerals that resist melting at elevated temperatures
  2. Immense pressure from overlying layers that dramatically elevates the melting point of the iron-nickel alloyAnswer
  3. C
    Rapid thermal convection that transfers heat continuously into the cooler lithosphere
  4. D
    Continuous frictional locking along deep transform plate boundaries that stabilizes the core

Answer

Immense pressure from overlying layers that dramatically elevates the melting point of the iron-nickel alloy
The physical state of matter depends on both temperature and pressure. While the temperature in the inner core is high enough to melt iron under surface conditions, the immense weight of all overlying layers generates millions of atmospheres of pressure. This extreme confining pressure forces the iron and nickel atoms into a tightly packed crystalline lattice, raising the melting temperature above the actual core temperature.

Step-by-Step Solution

1
Identify the primary chemical composition and thermal state of the inner core
The inner core is composed predominantly of an iron-nickel alloy at temperatures exceeding 5,000 °C.
Understanding composition establishes the baseline physical properties under standard conditions.
2
Analyze the physical relationship between confining pressure and the melting point of solids
Increasing pressure forces atoms closer together, which raises the temperature required for a substance to transition from solid to liquid.
Phase state depends on both temperature and pressure simultaneously.
3
Apply this relationship to Earth's center to determine why the inner core is solid while the outer core is liquid
At the center of Earth, pressure exceeds 3.3 million atmospheres, raising the melting point of iron-nickel above the core's actual temperature.
This explains the solid state of the inner core despite extreme heat.

Key Concept

Effect of extreme confining pressure on the melting point and physical state of Earth's internal layers
Estimated Time:45s
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Topics

Earth's Interior and Plate Tectonics

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