Unit 5 - Geologic Time

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Across
  1. 3. Informal unit of the geologic time scale consisting of the first three eons.
  2. 5. Current eon of Earth's geologic time.
  3. 9. Name of the precambrian shield in North America, much of it is exposed in Canada.
  4. 11. Very stable mineral that scientists use to age-date old rocks.
  5. 12. Smallest unit of the geologic time scale, measured in hundreds of thousands to millions of years.
  6. 13. When an usually large number of organisms disappear from the rock record at the same time.
  7. 15. Small rock fragment that falls to Earth, generates heat.
Down
  1. 1. First eon lasting 600 million years, life could not have existed due to extreme heat.
  2. 2. Small fragment of granite-rich crust formed during the Archean.
  3. 4. The record of Earth's history from 4.6 bya to the present.
  4. 6. Process of internal zoning with the heaviest materials sinking to the center and lighter materials accumulating near the surface.
  5. 7. Second-longest time unit in the geologic time scale, measured in tens to hundreds of millions of years.
  6. 8. Deep and most stable part of a continent, continental core formed from the Archean or Proterozoic microcontinents.
  7. 10. Remnant of the early Solar System found orbiting between the orbits of Mars and Jupiter, bombarded early Earth generating heat energy.
  8. 14. The longest time unit in the geologic time scale.