Final answer:
A piece of rock found on a beach that originated from a mountain top is an example of erosion, which is the process of wearing down and transporting earth materials by natural forces.
Step-by-step explanation:
The movement of a rock piece from a mountain top to a beach is an example of erosion. Erosion is the process by which the earth's surface is worn away by natural forces such as water, wind, and ice. This process includes the wearing down and transporting of rock and soil materials from higher elevations to lower areas, like beaches. Along coastlines, sediment transported by wave action often contains well-sorted gravel and sand, suggesting the particles have been moved and deposited by high energy processes like waves. Additionally, geological formations like cross-bedding in sedimentary rocks indicate the direction of water or wind movement which leads to sediment deposition. Erosion contributes to changes in the landscape, such as the formation of valleys and beaches, and is a significant part of the earth's geologic cycle.