The Beginning of the Universe

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Across
  1. 2. The second element to have formed in the entire universe.
  2. 6. At one point, the universe cooled down enough so protons and electrons can stay together to form particles called __________. (Hint: you cannot trust these particles because they make up everything)
  3. 7. The universe used to be a single dot that was super dense and ___.
  4. 9. The universe’s first element.
  5. 10. A scientific theory about the universe began.
Down
  1. 1. The history of the universe is divided into multiple periods called _________.
  2. 3. Is it possible that new evidence in the future can lead scientists to revise the Big Bang Theory? ___.
  3. 4. The universe has been doing this since it first formed.
  4. 5. Do we know what was there before the Big Bang? ___.
  5. 8. The universe is more than ______ billion years old (the blank is a spelled-out number, like forty-five).