How rock layers show time
New rock layers form on top of old layers, so the oldest layer is at the bottom.
Law of superposition: in rock layers that are not disturbed, the oldest layer is at the bottom.
Watch rock layers form
Sediment: small pieces of rock, sand, mud, and shells. Fossil: the remains or trace of a living thing from long ago.
Earth is about 4.6 billion years old. The geologic time scale divides this long history into parts.
Try it
Put the layers in order
- Click the oldest layer first.
- Click the next oldest layer.
- Continue to the youngest layer.
- Read what each fossil tells about the past.
Cliff:
Click the oldest layer first.
Your list from oldest to youngest shows here.
Quick check
Answer 5 questions. You see your score at the end.