The mantle is primarily composed of solid, but ductile, rock. It extends from the base of the Earth's crust to the outer core, which is approximately 2,890 kilometers (1,800 miles) to 2,900 kilometers (1,802 miles) deep. The mantle can be divided into two main regions based on its physical properties: the upper mantle and the lower mantle.
The upper mantle is the uppermost layer of the mantle, extending from the base of the crust to a depth of about 660 kilometers (410 miles). It is composed of rocks rich in magnesium and iron silicates, called peridotite. This layer is solid but exhibits some plasticity, allowing for slow movement and convection currents. These convection currents are responsible for driving plate tectonics, as well as the movement of heat from the core to the surface.
Below the upper mantle lies the lower mantle, which extends from about 660 kilometers (410 miles) to the outer core. The lower mantle is under immense pressure, causing the rock to become more dense and less plastic compared to the upper mantle. The rocks in the lower mantle are also primarily composed of peridotite, but they undergo a phase transition due to the increased pressure, forming a mineral called bridgmanite. This phase transition is responsible for the increase in seismic wave velocities observed at this depth.
Ultimately, the mantle reaches the Earth's core, which is divided into the liquid outer core and the solid inner core. The core is primarily composed of iron and nickel, and it is characterized by extreme pressure and temperatures. The mantle serves as a buffer between the core and the crust, transmitting the heat generated by the core and exhibiting dynamic behavior due to convection currents, making it crucial for the Earth's geological activity.
All the rest of the mantle- made of hard hot rock- till it reaches the core.
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