Weathering is the
breaking down of rock into smaller and smaller particles. Weathering processes include frost wedging, acid rain dissolution, root growth, wind particle abrasion, heat expansion cracking, hydraulic fracture, and rock tumbling in rivers and streams.
Erosion is the movement of weathered material from one place to another place through the agents of erosion: wind, water, ice, and gravity.
In tandem, weathering and erosion act to lower the high points, and raise the low points on the surface of the planet.