What process involves the gradual wearing away of the earth's surface?

The process that involves the gradual wearing away of the earth's surface is erosion. Erosion refers to the movement of rock particles and soil away from their original location due to various forces such as wind, water, and ice. Over time, these forces contribute to the breakdown and transportation of materials, reshaping landscapes and promoting changes in topography.

Weathering, while closely related to erosion, specifically deals with the breakdown of rocks and minerals into smaller pieces through physical, chemical, or biological processes. It does not involve the movement of these materials, which is the key distinction between the two processes.

Deposition occurs when materials transported by erosion are dropped off in new locations, leading to the accumulation of sediment. This is a separate stage in the overall cycle of sediment movement.

Transportation is the process by which eroded materials are carried from one place to another. This is often part of the erosion process but does not encompass the entire concept of wearing away the earth's surface.

Thus, erosion is the correct answer because it incorporates both the wearing away and the movement of earth materials, making it the comprehensive process described in the question.