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Deposition is the process by which wind or water sediment settles out in layers. Furthermore, over time, the remains of living things may harden in this sediment and change into fossils. After sediment is deposited the processes of compaction and cementation change the fragments into sedimentary rock. Compaction. At first, the fragments of rock lie loosely together. But gradually, over many, many years these thick layers build up. This build up becomes heavy and presses down on the layers beneath it. Compaction is the pressing down of layers forcing the sediments to fit closer together. Over millions of years, this process can squeeze fragments tightly together. The layers often remain visible in the rock and may be used to identify sedimentary rock. Cementation
During the rock cycle process, sedimentary rocks can become metamorphic or igneous rocks as they are buried in the planet's crust with younger layers of rock above them. Eventually they can metamorphose under heat and pressure at great depth, or melt to form new magma. Uplifting of rock layers by earth forces can bring rocks near the surface again at any point in the cycle. Igneous and metamorphic rocks can weather to form sediments that later become sedimentary rocks. Igneous rocks can metamorphose when subjected again to heat and pressure. Metamorphic rocks can metamorphose in repeat episodes or melt into magma, which later cools to form igneous rocks.