Sedimentary rock contains fragments of other rocks that have been broken down into small particles.
These particles are carried by glaciers, rivers, the wind, landslides, wave action, and many other modes of transportation. Fossilized plant and animal matter are commonly found in sedimentary rock.
Lithification is the process by which these particles become one solid rock, or sedimentary rock. It can occur by three separate processes: cementation, compaction, and desiccation.
Cementation occurs when binding minerals (like clay) or other substances form between the particles of sediment. While the rock is being cemented, more particles are transported on top of it. As the particles build up—and are also cemented—the weight and pressure from above causes the lower rock to reduce in volume, much like trash in a trash compactor.
Compaction causes desiccation, which is the squeezing out of water.
The process of lithification creates different layers of sediment in the rock, depending on what sediment is currently being deposited. In this way, sedimentary rock provides a time line for Earth’s history.
The different layers, or strata, can show what was occurring on Earth’s surface, and for how long, and what life forms were active.