s5 (a.a.) Fossils
Millions of years ago, a fish died and sank to the bottom of a lake. Before the fish could decay completely, layers of sediment covered it. Minerals in the sediment seeped into the fish’s bones. Slowly, pressure changed the sediment into solid rock. Inside the rock, the fish became a fossil. Fossils like the ancient fish provide evidence of how life has changed over time. Fossils can also help scientists infer how Earth’s surface has changed. Fossils are clues to what past environments were like.
Most fossils form when living things die and are buried by sediments. The sediments slowly harden into rock and preserve the shapes of the organisms. Fossils are usually found in sedimentary rock. Sedimentary rock is the type of rock that is made of hardened sediment. Recall that sediment is the material removed by erosion. Sediment is made up of rock particles or the remains of living things. Sandstone, limestone, and coal are examples of sedimentary rocks.
Fossils also provide evidence about the past climate of a region. For example, coal has been found in Antarctica. But coal only forms from the remains of plants that grow in warm, swampy regions. As you probably know, thick layers of ice and snow now cover Antarctica. The presence of coal shows that the climate of Antarctica was once much warmer than it is today.