Determining the numerical age of rocks and fossils.
The sediment of this area was laid down after ammonite A appeared million years ago, and before ammonite B became extinct million years ago.
Human effects and interactions Marine mammals:
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Ancient Rock Arches Sing Songs.
Postcards from the Universe.
By understanding the dates of these rocks, scientists can deduce the age of the nearby fossils.
Keokuk Quartz Geodes.