SURFACE ROCK Earth is made of three different types of rock igneous metamorphic and sedimentary Earth’s crust is made mostly of igneous and metamorphic rocks Sedimentary rock lies on top of the crust forming most of Earth’s surface Sedimentary rocks are formed of tiny particles of minerals sand dirt mud and even little bits of animal matter such as bone and the shells of dead sea creatures These particles are moved by weather Tiny particles of sediment add up to form mighty rock structures like this one displaying several different layers deposited over many years 4
and water until they settle in one place combined together This settled matter is called sediment Over thousands of years the particles of sediment are compressed and bonded together to form solid rock Sedimentary rock forms in layers and the layers are visible in the existing rock Shell fossils are visible in this limestone Limestone makes up about 10 percent of all sedimentary rock Sedimentary rock is the most common type of rock you see on the ground outside each day Think About It 5
HOW ROCKS ARE MADE Some sedimentary rocks are made when water wind and other natural forces cause rocks and earth to wear away These forces also move bits of rock and earth to new places In the new place pressure causes them to bond together Sometimes dissolved minerals seep into the spaces between the particles These minerals can harden The process of erosion leaves a layer of new rock in the bottom of a valley 6
into a kind of cement gluing the particles together into a layer of rock As noted earlier other sedimentary rocks are formed from the bones and shells of animals and sea creatures After sea creatures die these bits and pieces fall to the ocean floor where they become compressed and form rock Sedimentary rock is also formed when a body of water evaporates or dries up leaving the minerals contained within the water behind to harden into rock When liquid turns into gas or vapor it evaporates Vocabulary Steam is water in gas form and it is created when water evaporates from a body of water such as this river 7
