What is the primary mechanism by which land surface is worn away?

The primary mechanism by which land surfaces are worn away involves a combination of processes that are influenced by wind, water, and gravity, making "all of the above" the most accurate choice.

Wind action contributes significantly to erosion, particularly in arid environments where loose soil and sand can be easily transported. The force of the wind can scuff and lift particles off the ground, gradually wearing down the surface.

Water action is perhaps the most significant erosive force, especially through processes such as rainfall, runoff, and rivers. Water can erode land surfaces by transporting sediment and shaping the terrain over time. For example, flowing water can carve out valleys and create smaller streams through the continuous movement of sediment.

Gravity action plays a crucial role as well, particularly in areas of steep terrain. Gravity causes materials such as soil and rock to move downward, which can lead to mass wasting events like landslides and soil creep, further contributing to the wearing away of land surfaces.

Given that each of these forces contributes to erosion in various environments and conditions, acknowledging all three mechanisms as integral to the process of land surface wear provides a comprehensive understanding of erosion and sedimentation dynamics.