Rocket builds a tower of books. "The first book I put down is on the bottom," he says.
Raven points at a canyon photo with stripes of rock. "What do you notice about these stripes?"
Nova draws a glowing arrow up the canyon wall. "Think about Rocket's books," she says. "Which layer came first?"
Sedimentary rock is built layer upon layer.
Sand, mud and other bits pile up over a very long time.
Plants, animals and footprints can get trapped in the layers.
If conditions are right, they become fossils as the layers turn into rock.
Hard parts, like bones, shells or wood, are more likely to become fossils.
Each layer is older than the layer above it.
So the oldest rock is at the bottom. The youngest rock is at the top.
Fossils in low layers are older than fossils in high layers.
A sea animal with a shell dies and sinks to the sea floor.
Sand and mud slowly cover the shell.
More layers pile on top over a very long time.
The layers harden into rock. The shell is now a fossil inside it.
| Statement | True or false? |
|---|---|
| The oldest rock layer is at the bottom. | ? |
| Sedimentary rock forms in layers. | ? |
| Fossils form in just a few days. | ? |
| Footprints can be trapped in layers too. | ? |
You read rock layers like a pro! Tomorrow you make your own trace fossils.