Mantle is made of what type of rock

The Tablelands rock in Figure 3. Lower in the mantle, extreme pressures transform minerals and create rocks like eclogite Figure 3. It is formed from the crust as well as the uppermost layer of the mantle which is stuck to the underside of the crust. Tectonic plates are fragments of lithosphere. Beneath the lithosphere is the asthenosphere. Tiny amounts of melted rock dispersed through the otherwise solid asthenosphere make the asthenosphere weak compared to the lithosphere.

The weakness of the asthenosphere is important for plate tectonics because it deforms as fragments of lithosphere move around upon and through it.

Without a weak asthenosphere, plates would be locked in place, unable to move as they do now. This boundary is referred to as the core-mantle boundary. One idea is that it is minerals are undergoing another transition in this region because of pressure and temperature conditions, similar to the transition between the upper and lower mantle.

Other ideas are that small pools of melt are present, or that the differences in seismic properties are due to subducted slabs of lithosphere resting on the core-mantle boundary. The core is primarily composed of iron, with lesser amounts of nickel. Heat flows in two different ways within the Earth: conduction and convection. Conduction is defined as the heat transfer that occurs through rapid collisions of atoms, which can only happen if the material is solid.

Heat flows from warmer to cooler places until all are the same temperature. The mantle is hot mostly because of heat conducted from the core. Convection is a process in which a material that can move and flow may develop convection currents. Convection in the mantle is the same as convection in a pot of water on a stove. As the core heats the bottom layer of mantle material, particles move more rapidly, decreasing its density and causing it to rise.

The rising material begins the convection current. When the warm material reaches the surface, it spreads horizontally. The material cools because it is no longer near the core. It eventually becomes cool and dense enough to sink back down into the mantle. At the bottom of the mantle, the material travels horizontally and is heated by the core. It reaches the location where warm mantle material rises, and the mantle convection cell is complete.

Scientists know that the core is metal for a few reasons. If the surface layers are less dense than average, then the interior must be denser than average. Calculations indicate that the core is about 85 percent iron metal with nickel metal making up much of the remaining 15 percent. Also, metallic meteorites are thought to be representative of the core.

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