Earth 101 - Week 1: The beginning

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Across
  1. 5. The ___ is 4.55 billion years old
  2. 6. Stars produce heavier elements by ____ fusion
  3. 8. There are ___ naturally-occurring elements
  4. 9. The heaviest elements are produced during ___
Down
  1. 1. ___ have been on Earth for ~160,000 years
  2. 2. Larger stars have _____ lifespans
  3. 3. The Universe is 13.8 billion years old. We know this from:_____ estimates of the expansion rate of the Universe
  4. 4. There are ____ billion stars in the Milky Way
  5. 7. the Big Bang produced mostly ___ and Helium (plus some Li, Be, and B).