Ametamorphic rock can also be thought of as a rock that changes. what causes the rock to change? layers of sediment build up over time press down to form a new rock. rain, wind, freezing and thawing, and plant roots growing cause the rock to erode, leaving behind sediments. extreme heat and pressure from deep within earth cause changes to the rocks appearance, structure, and composition. the rock slowly changes over time into a new rock.