Question: Why does Earth have plate tectonics and continents?

Hannah Bentham answered on 18 Jun 2013:

The Earth has plate tectonics due to convection in the Mantle. The Earth’s interior is made up of 4 basic zones: the Crust (down to about 70 km), the Mantle (70-2981 km), the liquid Outer Core (2891-5154km) and then the solid Inner Core.

In the Mantle, the rocks move slowly over million of years due to convection (think of a lava lamp with hot blobs moving up and cold blobs moving down). There are many theories as to what pattern of convection we have, but currently geophysicists and geodynamicists think that the whole of the mantle convects together such that convection cells span from top to bottom. The motion of the cell is driven by the subduction of the cold oceanic plates from the surface as they descend through the mantle. Heat rises to the surface from the core-mantle boundary bringing hot rocks with it and the rocks explore out of the surface at hot spots like Hawaii. So you can see that the Mantle and the surface are directly connected. My research looks for subducted plates in the Mantle so we can find out more about Mantle convection, both in the present and the past.

The continents are formed from continental crust which is formed from igneous, sedimentary and metamorphic rock. Continental crust is less dense than the oceanic crust, so at convergent margins, the continental crust stays at the surface while the oceanic plate gets pushed down. The continental crust then gets reinforced and thinker by the lava from subduction zone volcanoes.