Geologic Time - Study Review

1. How old is the Earth?
2. Write the eras in order from most recent to oldest. Label each with their absolute dates and provide a description of each.
   
3. Write the periods of the Mesozoic and Cenezoic from most recent to oldest.
4. How do scientists know how old the earth is?

5. Create a timeline for the following events using absolute dates.

   a. Formation of the Earth and Moon

   b. Earliest life

   c. Early land plants

   d. Largest Mass Extinction (Permian-Triassic extinction event)

   e. Dinosaur Extinction (Cretaceous-Tertiary extinction event)

   f. “Lucy” Early Hominid
6. Explain the law of superposition.
7. If you start with 200 grams of Strontium-90, which has a half life of 28.8 years, how much Strontium-90 will you have after 6 half lives?
8. What do we mean by half life? What kinds materials do we use this term with?