Final answer:
Thermal (contact) metamorphism occurs deep within the Earth. It is a process where a pre-existing rock is altered by a change in temperature, pressure, or contact with chemically reactive fluids, resulting in the formation of a new rock.
Step-by-step explanation:
Thermal (contact) metamorphism occurs deep within the Earth. It is a process where a pre-existing rock, called the protolith, is altered by a change in temperature, pressure, or contact with chemically reactive fluids. This alteration causes the minerals in the rock to recrystallize, resulting in the formation of a new rock with different appearance and characteristics.