Earth in Space Practice Test

Accretion is the process where matter clumps together under gravity to build up larger bodies. Tiny particles collide and stick, and gravity then pulls in more material, leading to growth from dust grains to bigger objects like planetesimals and eventually planets or star-forming clumps. This idea explains how objects in a protoplanetary disk or a cloud of gas and dust gather mass over time.

The other terms don’t describe this growth mechanism: perspective is about viewpoints, diffusion is the spreading of particles from dense to sparse areas due to random motion, and rotation is the spinning motion of an object. None of these capture the gradual buildup of matter into larger bodies driven by gravity.