What is the main source of downward convection flow in the mantle called? The downward sliding characteristic of ridge-push is the result of what? What causes the thermal convection that drives plate motion? Is it the downward arm of convective flow in the mantle?
Here's your answer...
The heat driving mantle convection has three sources. "Primordial" heat (left over from the accretion and differentiation that led to the formation of Earth's core) contributes 20 to 50% of the heat. ... Mantle convection is the main mechanism by which this heat escapes from the interior of Earth.
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