AIMS Science Practice Test

Plate tectonics describes Earth’s outer shell as being broken into many moving plates that float on the hotter, plastic layer beneath them called the asthenosphere. These plates drift because heat-driven convection currents in the mantle move the rock, and gravity helps pull dense oceanic plates down at subduction zones while pushing at mid-ocean ridges. This combination of forces causes the plates to collide, slide past one another, or pull apart, leading to earthquakes, volcanoes, and mountain building. The idea that the surface is a single rigid shell isn’t accurate because the continents and oceans sit on separate plates that move relative to each other. The atmosphere doesn’t drive plate movement; its processes are atmospheric and surface phenomena, far removed from the deep-Earth forces that govern plate motion. The oceans aren’t the sole driver either, though interactions at oceanic boundaries and water loading can influence patterns of movement. The fundamental drivers are mantle convection and related forces like slab pull and ridge push.