Why is Earth still chemically changing through plate tectonics?

Earth remains chemically active because it is still undergoing planetary differentiation, a process where the planet separates into distinct chemical layers. This evolution is driven by mantle convection, which is powered by the decay of radioactive elements within the Earth's interior.123

Through plate tectonics, Earth continuously cycles material between the surface and the mantle. At divergent boundaries, new crust is produced from the mantle, while at subduction zones, crustal material is recycled back into the interior. During this cycle, the material undergoes ongoing chemical processing—transforming from basaltic to andesitic and eventually to granitic (continental) compositions through partial melting and crystallization.1456

This dynamic system ensures that Earth’s interior and surface continue to evolve chemically, even 4.56 billion years after the planet's formation. This pervasive, long-term tectonic activity is unique among the terrestrial planets and is facilitated by Earth's large size, which maintains high heat flow, and the presence of water, which softens the crust.14