Final answer:
Sedimentary rocks form when sediments are compacted and cemented under pressure over time, providing insight into Earth's history.
Step-by-step explanation:
The type of rock that forms when smaller rocks (also known as sediments) are pressed together under pressure over time is known as sedimentary rock. Sedimentary rocks are formed through the process of sedimentation, where particles and fragments from other rocks or organic material accumulate in layers, and with time, are cemented and compacted through the weight of overlying materials. Common examples of sedimentary rocks are sandstone, shale, and limestone.
These rocks are crucial for interpreting Earth's history as they often contain fossils and clues about the environment at the time of their formation. Sedimentary rocks contrast with igneous rocks, which solidify from magma or lava, and metamorphic rocks, which are formed from the alteration of existing rocks due to intense heat and pressure.