What are the two main environmental factors that drive metamorphism?

• A. Temperature and pressure
• B. Oxygen and humidity
• C. Magnetic field and gravity
• D. Sunlight and wind

Answer: (A)

Metamorphism mainly hinges on heat and pressure. When rocks are buried deeper in the crust, they experience higher temperatures that provide the energy for minerals to react, recrystallize, and form new minerals stable at those conditions. At the same time, the increasing pressure from overlying rocks (and any directed stresses from tectonic forces) forces the minerals to rearrange and compact, which creates textures such as foliation and changes in mineral stability. Fluids like water or CO2 can speed these reactions, acting as catalysts, but the core drivers are the elevated temperature and pressure.

The other factors listed don’t supply the necessary deep-Earth energy and conditions. Oxygen and humidity relate to surface weathering, not deep metamorphism. Magnetic fields and gravity aren’t energy sources that drive metamorphic changes, and sunlight with wind are surface processes that erode or alter rocks rather than metamorphose them.