Book 5, Question 44
Rock Clock Clues! Why Is Index Fossil a Useful Nickname?
An index fossil comes from a kind of living thing that was common and lived only during a certain stretch of time. If scientists find that fossil in a rock layer, it gives a clue about how old the layer is. It works a bit like a time label on the rock.
From the book
Page from A Million Whys Book 5
More fun facts
- Layers of rock are like chapters in a very thick book about Earth's history.
- As species appear and go extinct, the fossils in the rock layers change too.
- When the same kinds of fossils show up in rocks from different places, the rocks are about the same age.
- Fossils that help match rock ages this way are called index fossils.
- Scientists also date fossils using layers of volcanic ash found above and below them.
- As one science editor put it, no fossil is buried with its birth certificate.
Sources: U.S. Geological Survey, Science News Explores, Smithsonian Magazine
Questions kids ask
How do index fossils work like a clock?
Certain fossils lived only during a certain time. Finding them tells scientists the age of the rock.