History of the Earth

123456789101112131415161718192021222324252627282930
Across
  1. 3. the number of years that have passed since the rock formed
  2. 4. a vertebrate that controls its own body temperature and feeds milk to it's young
  3. 8. period during the first part of the Paleozoic era when life took a huge leap forward
  4. 9. era known as the "age of reptiles"
  5. 11. Geologists ________ that layers with matching index fossils are the same age
  6. 15. long units of time
  7. 16. when an element is unstable and releases energy in the form of radiation
  8. 19. when compared to another thing
  9. 20. animals without backbones
  10. 23. animal that lives part of it's life on land and part of it's life in water
  11. 24. dating used to find the age of plant and animal remains
  12. 25. animals with scaly skin that lay eggs with tough, leathery shells
  13. 26. radioactive _____________ is used by geologists to determine the absolute age of rocks
  14. 27. Period of the Paleozoic Era know as the "Age of Fish"
  15. 28. Geologists continually _______ the geologic time scale with new discoveries and new technology
  16. 29. Eras are subdivided into units of geologic time called
  17. 30. a gap in the geologic record
Down
  1. 1. causes losses in rock layers
  2. 2. used to determine the relative ages of sedimentary rock layers
  3. 5. time in earth's history with only single-celled organisms
  4. 6. animal with a backbone
  5. 7. the preserved remains or traces of living things
  6. 10. an event during which many types of living things became extinct at the same time
  7. 12. its age compared to the ages of other rocks
  8. 13. period of time when mammals first appeared
  9. 14. dating used to find the age of rocks
  10. 17. period of the Mesozoic era that ended with the extinction of the dinosaurs
  11. 18. a record of the geologic events and the evolution of life forms
  12. 21. Period of Cenozoic Era known as "Age of Humans"
  13. 22. Last period of Paleozoic Era when Pangaea forms