Divergent Boundaries

The story of the continents begins at the places where the great plates of the Earth's crust are being torn apart. At a divergent boundary, the plates do not collide or grind past one another; instead, they pull away from each other. This separation is not a quiet event — it is the very process by which new crust is born.

As the plates move apart, molten rock from deep within the Earth rises up to fill the gap. When this magma cools and solidifies, it forms fresh crust along the boundary. Because new material is constantly being added here, these sites are called spreading sites. The name captures the essence of what happens: the seafloor literally spreads outward from a central line, pushing the older crust aside as newer crust forms in the middle.

The most famous and best-studied example of a divergent boundary is the Mid-Atlantic Ridge. This is an enormous underwater mountain range that runs down the middle of the Atlantic Ocean. At this ridge, the plates carrying the Americas are moving away from the plates carrying Europe and Africa. Specifically, the American Plate is separated from the Eurasian Plate and the African Plate along this boundary. The ridge is the visible scar of that separation — a place where the ocean floor is actively being created and the Atlantic is slowly widening. …