Across
- 3. time it takes for half the atoms of an isotope to decay
- 5. gap in the rock layer due to erosion or periods without deposition
- 6. era of recent life that began about 66mil years ago
- 9. next smaller division of geologic time after the period
- 12. third longest division of geologic time
- 13. middle era of earths history
- 15. age in years or other objects(can be
- 16. imprints of an organisms
- 17. indent of something
- 18. type of body fossil that forms when crystals fill a mold
- 19. chlorophyll containing photosynthetic bacteria
- 20. longest part of earths history
Down
- 1. age of something compared with others
- 2. era of ancient life
- 4. second longest division of geologic time
- 7. group of organisms that normally breed amongst themselves
- 8. division of earths history into time units
- 10. organism with 3 lobbed exoskeleton
- 11. longest subdivision in the geologic time
- 14. thin film of carbon residue preserved as a fossil