* Divergent Plate Boundaries: These are areas where tectonic plates move apart. As they pull away, magma from the Earth's mantle rises to the surface, cools, and solidifies, creating new crust. This process is called seafloor spreading and occurs primarily at mid-ocean ridges.

* Convergent Plate Boundaries: These are areas where tectonic plates collide. At these boundaries, older crust is typically destroyed through subduction (one plate sliding beneath the other) or through mountain building (plates pushing against each other).

* Transform Plate Boundaries: These are areas where tectonic plates slide past each other horizontally. No new crust is created or destroyed at these boundaries.

Here's a simple analogy: Imagine two conveyor belts moving in opposite directions. The space between them represents a divergent plate boundary. As the belts move, new material is added to the belts from a source beneath them. This new material represents the new crust being formed at the divergent boundary.

Key Points:

* The vast majority of new crust is formed at mid-ocean ridges.

* The rate of seafloor spreading varies, but it's generally on the order of a few centimeters per year.

* The process of seafloor spreading is a key part of the theory of plate tectonics, which explains the movement and interaction of Earth's tectonic plates.