Which statement best defines a divergent boundary?

• A. A boundary where two plates collide, often forming mountains.
• B. A boundary where two plates slide past one another horizontally.
• C. A boundary where two plates move apart, forming new crust as magma rises to the surface.
• D. A boundary where plates subduct beneath one another.

Answer: (D)

At divergent boundaries, tectonic plates move away from each other. As they separate, magma from the mantle can rise into the gap, cool to form new crust, and create new lithosphere—this is the process of seafloor spreading at mid‑ocean ridges. This combination of moving apart and forming new crust is what defines a divergent boundary most clearly. The other boundary types involve different interactions: convergent boundaries collide and can push crust up into mountains or drive one plate beneath another (subduction), and transform boundaries slide past one another horizontally.