Final answer:
Metamorphic rocks are exposed at Earth's surface primarily due to erosion, which occurs as geological activity brings these rocks closer to the surface where they are weathered and eroded over time.
Step-by-step explanation:
If metamorphism occurs at depth, we see metamorphic rocks at Earth's surface primarily due to erosion. Although metamorphic rocks are formed under conditions of intense heat and pressure at considerable depths within the Earth, geological activity such as uplift and mountain building processes brings these rocks closer to the surface. Over time, weathering and erosion act on these raised regions, eroding away the overlying material and exposing the metamorphic rocks beneath. In particular, during a continental collision, high-grade metamorphic rocks can be found near the center where uplift and erosion are most prevalent. This geological activity is a key factor in recycling rocks throughout geologic time and is part of the overarching plate tectonics that shape our planet's surface.