In the canyon visitor center, a ranger hands Raven a gray rock. It is covered in tiny shell shapes.
"These are fossils of sea animals," the ranger says. "Rocks like this come from the canyon walls."
Rocket looks around at the dry desert. "Sea animals? Up here? There is no ocean for miles!"
"What do you notice about where the fossil was found?" Raven asks.
Nova blinks thoughtfully. "Would you like a hint? Fossils show what lived in a place when the rock formed."
A fossil is the remains or traces of a living thing from long ago, kept in rock.
Many Grand Canyon rock layers hold fossils of sea animals. These include sponges and animals called crinoids and brachiopods.
Sea animal fossils are evidence that a sea once covered that place when those layers formed.
Other layers hold fossil plants and footprints of reptiles and scorpions. Those show times when the place was land.
The fossils in each layer help scientists tell the order the layers formed. They also show how the place changed.
Here is a model of three rock layers at one cliff.
| Layer | Fossils found |
|---|---|
| Top layer | sea shells |
| Middle layer | fern leaves and footprints |
| Bottom layer | no fossils |
| Statement about the cliff | True or false? |
|---|---|
| The middle layer formed when the place was land. | ? |
| The top layer formed when the place was covered by water. | ? |
| The top layer is older than the middle layer. | ? |
Fossils are like snapshots from long ago.
A layer with sea animal fossils formed under water.
A layer with plant fossils or footprints formed on land.
Stack the clues in order, and you can read how a place changed.
You read Earth's history like a detective! Tomorrow you test how water moves land.