16 - Human Transportation
We live on top of rocks – the Earth’s surface. There are three basic types of rocks — igneous, sedimentary, and metamorphic — and each type is made a different way. Igneous rocks are made from cooled lava. Sedimentary rocks are made from small pieces of other rocks stuck together. Metamorphic rocks are formed when other rocks are heated or pressed, or both. One type of rock can change into another type of rock as the Earth’s surface shifts and changes. It takes the right conditions and a lot of time.