A convection current is when hot matter rises and colder matter falls because of uneven heating. These convection currents are important because the tectonic plates are on top of the mantle where the convection currents take place, and they are the cause of the plates' movement.

In the early twentieth century, a geologist named Harry Hess proposed the idea of Sea-Floor Spreading. As magma comes through mid-ocean rifts because of the convection currents in the mantle, it hardens and spreads the oceanic plates apart. His evidence was that rocks nearer to rifts were younger than rocks farther from the rifts. Also, similar bands of matching rock were found on either side of the rifts. Finally, from earthquake data, there was proof that the oceanic crust was sinking into the mantle at trenches, which was where the magma that rose up came from. This theory was important to Wegener's theory of continental drift because it provided a reason for why the plates moved.

The theory of Plate Tectonics is that the lithosphere, the rigid outer layer of the earth, is divided into large slabs of rock, or plates, that move very slowly and cause natural disasters such as earthquakes through the various movements they make. This theory is also part of many other theories, such as the theory of Continental Drift and the theory of Seafloor Spreading.

There are three types of stress. These are compression, tension, and shearing. Compression is when two plates come towards each other. Tension is when two plates move away from each other. Shearing is when two plates move past each other in opposite directions.

A convergent boundary is created by compression, where two plates are coming together. This type of boundary is where mountains, volcanoes, or trenches can form.