science crosswords

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Across
  1. 2. one of the three long units of geological time between the Precambrian and the present
  2. 5. the age of a rock compared to age of other rocks
  3. 6. the age of a rock given as the number of years since the rock formed
  4. 8. the process of determining the age of an object using the half-life of one or more radioactive isotopes
Down
  1. 1. the geological principles that states that in horizontally layers of cemetery rocks each layer is above it and younger than the layer below it
  2. 3. the procces of nuclie of radio active
  3. 4. the preserved remains or traces of an organism that lived in the past
  4. 7. a gab in the geological record that shows where rock layers have been lost due to erosion