The Laying of Sedimentary Rocks Over Time

Sedimentary rock forms from bits of rocks deposited over time by wind and or water. Rocks occur in all sizes. It is the tiny amounts of mud, pebbles and sand grains and smaller rock particles that can form sedimentary rock. Sediment can also contain the remains of once living things. This may be bones, shells, droppings, leaves or stems. Wind and water carries sediment and deposits it in layers usually in a lake or ocean bottom.  The processes that turn sediments into solid rock are compaction and cementation.

Erosion

Destructive forces are constantly breaking up and wearing away the rocks of Earth. The forces include grinding ice, waves, rain, and heat. Erosion occurs when these agents loosen and carry away the fragments of rock or once living things somewhere else.

Deposition Environments: a place where sediments collect.

Eventually, wind or water will drop these fragments. They will accumulate in low valley or river bottom. 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 process of compaction the minerals in the rock are dissolving. The minerals fill in the spaces between sediment particles. Cementation is the process of sediment being glued tightly together. The processes of erosion, deposition, compaction and cementation may occur over millions of years transforming rock fragments into solid rock.