Plate Tectonics: Piecing It All Together

Let's draw lines on the mid-ocean ridges and trenches; these form the boundaries of tectonic plates.The continents ride on top of the plates.

This is a cross-section of the Earth; plates spread apart at mid-ocean ridges, and go back into the Earth at trenches.

Here's a closer view:

Plates are spreading apart at mid-ocean ridges:

Plates are coming together at trenches:

Plates are moving past one another at places like California's San Andreas fault:

Plate motion is slow by human standards; just a few inches per year.