What are sedimentary rocks?

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Horizontal Bedding in Cedar Mesa Sandstone

Sediment is made up of solid, loose pieces of rocks (in the form of sand, silt, clay, and gravel), or the remains of living things found at the surface of the Earth. Sediment is material that has been eroded and deposited by wind, running water, waves, and ice.

Sediment can also form from material left behind by the evaporation of seawater, or the settling of the remains of animals and plants in oceans, lakes, and swamps. In certain conditions, and over a very long period of time, sediment can become compacted and cemented into sedimentary rock. Sedimentary rock is often found in layers. One way to tell if a rock sample is sedimentary is to see if it is made from grains.