Across
- 3. rock layer formed when lava cools on the Earth's surface
- 5. a fossil that shows the activities of ancient organisms
- 9. fossil made by a extremely thin coating of carbon on rock
- 12. a person who studies fossils
- 15. a record of the geologic events in Earth's history
- 17. the process in which radioactive elements break down
- 18. a group of organisms that has completely died out
- 19. the exact age of a rock
- 21. widely distributed fossils of an organism the lived for a short time
- 23. a mold fossil that was filled in and turned into a stone replica of the organism
Down
- 1. parts that eras are split into
- 2. a crack in Earth's surface on which rocks move
- 4. A gap in the geologic record that shows where rock layers have been lost due to erosion
- 6. when rock layers are horizontal, each rock layer is older than the one above it
- 7. rock layer formed when magma hardens below the Earth's surface
- 8. three long units of time that only end with mass extinctions
- 10. type of fossil that is a hollow space in sediment in the shape of the organism
- 11. a type of fossil that is fully or partly replaced by minerals
- 13. the time it takes for half the atoms in a radioactive element to decay
- 14. the age of a rock in comparison to another rock
- 16. a collection of ice and dust that orbits the sun
- 20. how organisms change over long periods of time
- 22. a way that nature shows us the organisms that lived in the past