Here's why:
* Pressure and Melting Point: The melting point of a substance is influenced by pressure. As pressure increases, the melting point also increases.
* Lower Mantle Conditions: The lower mantle experiences immense pressure from the weight of the Earth's crust and upper mantle above it. This intense pressure raises the melting point of the mantle rocks far beyond the temperatures present in the lower mantle.
* Solid State: Although the lower mantle is very hot, the pressure is so high that the rock remains in a solid state, even though it behaves like a very viscous fluid over long periods.
Let me know if you have any other questions!
