Question

a geologist discovers an unusual rock formation containing alternating layers of metamorphic and sedimentary rocks. which of the following sequences of events in the rock cycle most likely explains this observation?

• subduction → metamorphism → uplift → erosion → sedimentation → lithification (repeated)
• metamorphism → melting → crystallization → weathering → sedimentation (repeated)
• sedimentation → lithification → metamorphism → uplift → erosion → sedimentation (repeated)
• volcanism → weathering → sedimentation → metamorphism → uplift (repeated)

Explanation:

To form alternating metamorphic and sedimentary layers, we need a cycle that first creates sedimentary rock, then transforms it to metamorphic, then returns to conditions that form new sedimentary rock, repeated.

1. First, sedimentation (depositing sediment) and lithification turn that sediment into sedimentary rock.
2. Then, metamorphism alters that sedimentary rock into metamorphic rock (via heat/pressure, e.g., from burial or subduction).
3. Uplift brings the metamorphic rock to the surface, where erosion breaks it down into sediment.
4. New sedimentation of that eroded material starts the cycle again, creating a new sedimentary layer on top of the metamorphic rock. Repeating this creates alternating layers.

Other options fail: The first skips initial sedimentary rock formation, the second includes melting (creating igneous rock, not alternating metamorphic/sedimentary), the fourth starts with volcanism (igneous rock, not the required sequence).

Answer:

C. Sedimentation → lithification → metamorphism → uplift → erosion → sedimentation (repeated)