How Fossils Form How fossils show that life on Earth has changed

Fossils are things that have lasted from living things that died long ago. Traces of ancient animals and plants left as molds, casts, and prints. Some fossils show us the shapes of plants and animals of the past. Some fossils are also remains, which show actual bones, shells, or teeth.

A mold is the shape of a plant or animal left in sediments when the rock formed. A cast forms when mud or minerals fill a mold. The cast has the exact same shape of the animal that made the mold. Imprints are molds of leaves or other thin objects. Some imprints are of animal wings or feathers.

Fossils often form in sedimentary rocks, such as limestone and shale. Steps: 1. The soft parts of an animal decompose 2. Hard parts of the animal, such as shells or bones, are slowly buried under layers of sediment. 3. Over a long time the sediment turns into rock. 4. Movement of the Earth’s crust brings the rock and fossils closer to the surface. Wind and rain wear away the rock on top of the fossils.

Plant fossils are much less common than animal fossils. This is because plant parts are more easily destroyed as rocks form.

Dinosaurs became extinct long before there were any scientists to study them. But today scientists can use fossils to learn how dinosaurs looked and lived. Scientists use fossils to put together dinosaur skeletons. The skeletons show how large the dinosaurs were, and the teeth fossils show what kind of food they ate.