Grades 4 to 5

Fossils are evidence of animal and plant life that has been preserved within the Earth’s crust. Fossils can be actual parts of an animal or plant. They can also be traces of an animal, such a footprint or even its waste! Preserved traces of animals are important because they can reveal information about how the animal behaved long ago and what it ate.

Fossils are typically created when an animal or plant dies. Before it has a chance to decay, it is covered with mud, rocks and sand called sediment. As sediment builds up on top of the animal or plant, it becomes hard and forms rock. Many of the fossils we find took place in a body of water. Over time the animal and plant remains were washed away, leaving a mold of the remains. If minerals filled the mold, a cast or replica of the animal or plant is left behind. Fossils can be found in bogs, quicksand, amber, volcanic ash and tar pits.

You can see a variety of plant and animal fossils. Just take a tour of the virtual fossil museum by clicking on this link:

The fossil record
Studying fossils and how life developed and progressed throughout history is called paleontology (pay-lee-un-tall-o-gee), and people who study it are called paleontologists. The location of fossils within the Earth’s crust is also important. It is part of the fossil record, which reveals a lot about the history of the Earth. Scientists discovered in the early 1800s that similar fossils were found in similar rock around the globe, and they always occurred in a similar order. Based on that, scientists developed a system for dating the age of the fossils and created the geologic time scale that shows Earth’s history.

Show students how sediment forms fossils.

Fossils can come in many forms. Upper left: The limestone rock has the shape of a trilobite, a small sea creature that made an impression that was filled in with minerals when the rocks was formed. Upper right: Teeth are coated with enamel that helps preserve them. This rhinoceros tooth helps scientists know what kinds of foods were eaten and how old the animal was when it died. Bottom: This leg bone from a mastodon helps scientists determine how large the animal was when it died.