Module 18 Geologic Time Scale

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Across
  1. 1. walking upright on two legs
  2. 3. the ancient geographic setting of an area
  3. 6. egg with a shell, providing a complete environment for a developing embryo
  4. 7. very stable and common mineral that scientist often use to age-date old rocks
  5. 8. a building block of proteins
  6. 10. occurs when sea level falls, causing the shoreline to move seaward, and results in shallow-water deposits overlying deep-water deposits
  7. 14. process in which a planet becomes internally zoned, with the heavy materials sinking toward the center and the lighter materials accumulating near its surface
  8. 16. sudden appearance of a diverse collection of organisms in the Cambrian fossil record
  9. 17. name given to the Precambrian shield in North America
  10. 18. large mat or mound composed of billions of photosynthesizing cyanobacteria
  11. 19. metal that is rare in rocks at Earth's surface but is relatively common in asteroids
  12. 20. organism composed of one or more cells each of which usually contains a nucleus
  13. 23. fossils of various multicellular organisms from about 635 mya
  14. 24. microscopic, photosynthetic prokaryotes that formed stromatolites and changed early Earth's atmosphere by generating oxygen
  15. 25. edge of a continent along which there is no tectonic activity
  16. 26. ancient continent formed during the Proterozoic that is the core of modern-day North America
Down
  1. 2. metallic or silica-rich object, 1 m to 950 km in diameter, that bombarded early Earth, generating heat energy
  2. 3. microscopic organisms that are the basis of marine food chains
  3. 4. the top of a craton exposed at Earth's surface
  4. 5. a sedimentary rock deposit that contains oxidized iron
  5. 9. species to which modern humans belong
  6. 11. unicellular organism that lacks a nucleus
  7. 12. alternating bands of iron oxide and chert, an iron-poor sedimentary rock
  8. 13. a small fragment of granite-rich crust formed during the Archean
  9. 15. continental core formed from Archean or Proterozoic microcontinents; deepest (as far as 200 km into the mantle) and most stable part of a continent
  10. 21. occurs when sea level rises and causes the shoreline to move inland, resulting in deeper-water deposits overlying shallower-water deposits
  11. 22. a small fragment of an orbiting body that has fallen to Earth, generating heat; does not completely burn up in Earth's atmosphere and strikes Earth's surface, sometimes causing an impact crater