What causes convection currents in earths mantle?
Density differences in the rock are the cause of the movement (the convection, which is the movement of mass through the system because of differences in density). Heat is the primary cause of the density differences. When a substance is heated, there is usually (almost always) some expansion. Expansion lowers the mass per volume, which is density. Less dense things want to move above higher density things (or the higher density things want to move under the less dense things, which is saying the same thing in the other way). The heat in the mantle is produced by the decay of radioactive elements. The heat tries to spread out evenly but it takes a long long time for heat to move by conduction (by direct transfer of energy to adjacent materials). As a result, some areas of the mantle are hotter than others, and start to try to rise. Of course, there is material above it that is in the way, so the hot areas tend to move in big bubbles (if you know what a lava lamp is, the way the goop mo
