Keep that engine rolling - plate tectonics – the mechanism
So what exactly is the evidence for the mechanism – what exactly keeps this ‘engine’ called the Earth running? In fact, the mechanisms by which plate tectonics work are actually poorly understood and research is ongoing. Measurements of temperature from bore-holes and mines tell us that the temperature of the earth increases with depth by an average of two or three degrees Celsius per 100 meters. The source of this heat is radioactivity in the planets core.
Thermal convection
The movement of this heat or thermal convection is the most popular explanation for plate tectonics. In this concept, hot magma moves upwards because it is less dense and thus lighter than the surrounding fluid (this is why hot air balloons rise). It gradually cools as part of the earths crust and falls at subduction zones because it denser and therefore heavier than the surrounding fluid. It then heats up again completing the cycle, and therefore moving the plates on the surface like a factory conveyor belt. The temperature of the lithosphere supports this explanation: it is hotter around ridges and cooler around subduction zones. There are many models for the exact nature of the convection currents inside the earth, some are more complicated and involve many layers of convection currents.
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