Footnotes for Unit 1 - Many Planets, One Earth

  1. American Museum of Natural History, "Our Dynamic Planet: Rock Around the Clock,"
  2. Peter D. Ward and Donald Brownlee, Rare Earth: Why Complex Life Is Uncommon in the Universe (New York: Springer-Verlag, 2000).
  3. U.S. Geological Survey, "Radiometric Time Scale,", and "The Age of the Earth,"
  4. Paul F. Hoffman and Daniel P. Schrag, "Snowball Earth," Scientific American, January 2000, pp. 68–75.
  5. Andrew Knoll, Life on a Young Planet: The First Three Billion Years of Evolution on Earth (Princeton University Press, 2003), p. 23.
  6. University of California Museum of Paleontology, "Cyanobacteria: Fossil Record,"
  7. Knoll, Life on a Young Planet, p. 42.
  8. "Did the Snowball Earth Kick-Start Complex Life?",
  9. Stephen Jay Gould, Wonderful Life: The Burgess Shale and the Nature of History (New York: Norton, 1990).

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