What best describes a fault in the Earth’s crust?

• A. A rock layer formed by sedimentation.
• B. A fracture along which movement has occurred.
• C. A large body of intrusive igneous rock.
• D. A process that preserves fossils.

Answer: (B)

A fault in the Earth's crust is a fracture along which movement has occurred. This means rocks on opposite sides of the crack have shifted relative to each other due to tectonic stresses, which is why faults are associated with earthquakes as energy is released during displacement. The other descriptions refer to different features: a rock layer formed by sedimentation is a sedimentary layer; a large body of intrusive igneous rock is a pluton or intrusion; a process that preserves fossils is fossilization. So the defining idea is the displacement that happens along a crack in the crust.