Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Sedimentary Rocks…..Rock? Read, highlight, Questions on Schoology! All over the United States we have very beautiful and strange scenery. South Dakota has the Badlands National Park with its jagged peaks, steep cliffs, and deep canyons sculpted in colorful rock that is layered like a birthday cake. The layers of rock are red, orange, pink, yellow, or tan. These rocks, like many of our other breathtaking rock formations developed over millions of years as tiny pieces of mud, sand, and volcanic ash were deposited in thick layers. The mud and sand slowly changed into sedimentary rock. These rock formations were exposed when the harsh sun, wind, and water wore away the surrounding material. What were left were the layers of history in the form of sedimentary rocks. If you put some muddy water in a jar and let it set a few days, what would you see? The water would become clear. There would be layers of dirt and stones at the bottom. This is called sediment. Sediment is small, solid pieces of material that come from rocks or living things. The rocks and living things have been broken apart by weathering. Wind, water, and ice break down rocks and minerals into smaller particles. In addition to particles of rock, sediment may be pieces of bone, shells, leaves, plants, bark, and other parts of living things. These pieces of sediment are what sedimentary rocks are made from. Sedimentary rocks only make up about 10 percent of the Earth’s rocks we see. Even though these rocks are only a small amount of all the rocks on Earth, they help us to know what happened in Earth’s history. The sediments form layers with the newest layers on top of the old ones. This process is called Stratification. As we look at the layers we can see what happened in history. Geologists can study fossils that were cemented into the layers of the rock. These fossils tell us about what type of living creatures were alive during different time periods. Sedimentary rocks are the only type of rock that has fossils in them. Most sedimentary rocks are formed through a series of process: erosion, deposition, compaction, and cementation. Running water, such as streams and rivers, helps form sedimentary rocks. The water carries the broken pieces of rock, this is called erosion. Wind and glaciers can also cause rocks and sediments to break down. The sediments are then dropped in layers wherever the current, wind flow slows down, or as glaciers melt. This is called deposition. After the layers are deposited, sedimentary rocks begin to form. This can happen in one of three ways. A process called compaction can form them. Compaction happens when layers of sediment are squeezed together. The pressure of the rocks on top causes this to happen. Sedimentary rocks can also be formed by cementation. Cementation happens when water evaporates out of the layers of sediment and the minerals are left behind. They "glue" the pieces of rock together. Cementation is kind of like building a brick wall. The bricklayer puts a mixture of sand and water between the bricks. This layer hardens as it dries, and the bricks stick together. Sedimentary rocks are formed almost the same way. The minerals between the rocks dry and stick the pieces together. Sedimentary rocks are classified based on the types of sediments that make them up. Clastic rocks are made from pieces of other rocks. They are formed by compaction and cementation. Clastic rocks can range in size from tiny particles of soil to huge boulders. Conglomerates and breccias are types of clastic rocks that have larger pieces of rock inside them. The only difference between the two is that conglomerates have rounded stones in them and breccias have jagged stones. Shale and sandstone are other types of clastic rocks, which are made from tinier bits of rocks like clay and sand. Conglomerate Breccia Sandstone The third kind of sedimentary rock is called organic. Organic rocks form from decayed plants and animals and not necessarily from other rock fragments. Remember we discussed organic to mean once living things. They are usually formed in oceans or swamps. The decayed material is compacted into rock. Two common organic rocks are limestone and coal. Limestone if formed because animals have calcium in their shells and bones. After the animal dies the calcium combines with other elements and hardens into a rock. Because limestone is directly made from animals it is common to find fossils in it. Coal is formed from water animals and plants that died millions of years ago and were squashed into the ground. Ohio has a lot of coal rocks. The last type of rock is a chemical sedimentary rock. Chemical sedimentary rocks are formed when water evaporates and leaves behind minerals that harden into rock. A great example of this kind of rock is salt. So remember when you're eating salt, you're eating a rock. It's a rock called halite. Sedimentary rocks give us important resources. Most ground water is found in sedimentary rocks. Coal, oil, and natural gas are found in these rocks as well. Sedimentary rocks also give us building materials. Iron is used for making steel. Limestone is made into cement. It is also cut to make blocks for large buildings. Where would we be without sedimentary rocks? Sh