Rock strata are described as:

• A. Mineral crystals formed by cooling.
• B. Layers of sedimentary rock deposited over time.
• C. They are always found at Earth's core.
• D. Rocks formed by metamorphism of granite.

Answer: (B)

Rock strata are the layered arrangement of sedimentary rocks formed by sediments being deposited over time. Each layer records a period of deposition, so the sequence preserves a history of past environments, with younger layers deposited on top of older ones. This layering is what we mean by strata, and it often contains fossils that help tell the relative ages of the layers. This concept differs from mineral crystals formed by cooling, which describes igneous rocks that crystallize from molten material rather than accumulate in layers. Strata aren’t tied to the Earth’s core; they occur in the crust where sediments settle in water or on land. Rocks formed by metamorphism of granite involve changes due to heat and pressure to create new minerals and textures, not the horizontal layering produced by sediment deposition.