Science
How does a fossil form?
A fossil forms when the remains or traces of a once-living thing are preserved in rock over thousands to millions of years. Usually, minerals slowly replace buried bone or shell, turning it to stone and capturing a record of ancient life.
See it in motion.
Watch a 2-minute animated lesson that shows exactly how a fossil works.
Step by step
- 1An organism is buried quickly by sediment after death.
- 2Soft parts usually decay; hard parts like bone remain.
- 3Over ages, minerals seep in and replace the original material.
- 4The remains turn to rock, preserving their shape.
- 5Fossils reveal the history of life and help date rock layers.
Frequently asked questions
- How does a fossil form?
- Remains get buried in sediment, and over long ages minerals gradually replace the hard parts, turning them to stone while keeping their shape.
- Why are fossils usually bones and shells?
- Soft tissues decay quickly; hard parts like bones, teeth, and shells last long enough to be mineralized and preserved.
- How do scientists know a fossil's age?
- By dating the surrounding rock layers and using radioactive decay (radiometric dating) to estimate how long ago it formed.