The Earth is comprised of huge layers, each of which has distinct characteristics. The majority of the Earth, about 80 percent, is made up of the mantle, which is the layer right next to the Earth's core, according to ThinkQuest.com. Inside the mantle, convection currents constantly are moving, shifting molten rock about and moving the plates of the Earth's surface. Four main factors are responsible for mantle convection currents.
Pressure and Temperature
The mantle is made up of molten rock and trapped gases. All of this matter is under pressure because of Earth's gravitational pull, according to Don Anderson of the California Institute of Technology. This intense pressure, along with the atomic structure of the elements in the mantle, makes chemical reactions happen that create heat. The creation of this heat energy affects where the atoms of matter in the mantle go. If pressure is not as high, atoms can move more freely. If pressure is extreme, a lot of energy is needed to get the atoms to shift.
As explained by the University of Oregon, when atoms in the mantle are exposed to heat, they deal with the extra energy by spreading out. This makes the matter in the mantle less dense. Less dense matter always will rise because it isn't as heavy. The matter in the mantle thus rises when enough heat has been produced close to the core. When matter cools off, the atoms come back together, so the matter in the mantle becomes less dense and eventually sinks. The amount of pressure at a given point in the mantle impacts the density of the matter, so pressure is a big factor in whether the convection current moves.
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As the Earth spins, some of the Earth's heat energy escapes out into outer space. The Earth thus is cooling naturally over time, and when the matter in the mantle gets close to the top of the Earth, some of its heat is lost as part of this process, according to Anderson. This makes the matter in the mantle denser, so it sinks back down toward the core. The more heat is lost through the Earth's natural cooling processes, the faster the mantle convection current can move.
The Earth is spinning rapidly while convection currents are moving in the mantle. This spinning pulls the matter in the mantle around. The Earth's rotation thus affects where the mantle convection currents travel, which in turn affects how much heat and pressure is involved at any point of the current, according to R. Hide of Royal Society Publishing.