Why do sedimentary rocks have layers?

The layers found in sedimentary rocks are the result of various sediments (small broken pieces of rock) being deposited over time; these sediments may have been deposited by wind, water, ice, and/or gravity at various times and compacted on top of one another to form layers in a sedimentary rock that may contain sediments from different rock types.

Consider this: suppose you have three different containers: sand, sugar, and dirt. These are your "sediments". You take a large clear box and fill it with all of your dirt (the oldest layer), all of your sugar (the second middle layer), and all of your sand (the third newest layer). If you look at the clear box, you will see that you have three layers: a dark brown bottom layer, a white middle layer, and a sandy beige top layer.

In terms of rocks, this is equivalent to "dumping" rocks through erosion, where sediments eventually compact together under intense pressure and time to form layers that ultimately form a rock.

Sedimentary rocks have layers because they are formed through the accumulation and compaction of sediments over time. These sediments, which can include particles of sand, silt, clay, and organic material, are often deposited in horizontal layers by water, wind, or ice. As new layers of sediment are deposited on top of older ones, the weight of the overlying sediment compacts the lower layers, causing them to become lithified into solid rock. Over time, this process results in the formation of distinct layers, or strata, within the sedimentary rock. Each layer may contain different types of sediment, as well as fossils or other features that provide clues about the environmental conditions in which they were deposited.