What is the process by which sedimentary rocks are formed from pre-existing rocks or organic material?

• A. Weathering
• B. Erosion
• C. Lithification
• D. Metamorphism

Answer: (C)

Lithification is the process that turns loose sediments into solid sedimentary rock. After rocks are broken down by weathering, the fragments or organic remains settle and accumulate as layers. Burial under more sediment compacts the grains, squeezing out water and reducing pore space. Minerals carried by groundwater then precipitate and form a natural cement that binds the particles together. This combination of compaction and cementation is what solidifies the sediment into rock. Metamorphism would alter rocks under heat and pressure, not form sedimentary rock. Weathering and erosion create and move the sediments, but lithification is what converts them into sedimentary rock.