# Pre/Post-Test Key

1. Current scientific evidence shows that the Earth is:
c) more than 4 billion years old

2. Look at the diagram below representing layers of rocks and the fossils buried in them.
a) Circle the oldest layer. (The bottom layer is circled)
b) Explain how you know which layer is the oldest. (Hint: The Law of Superposition might help you.)
According to the Law of Superposition newer rock layers form on top of already existing layers. As more and more layers are deposited, the older rock layers end up at the bottom and the newer ones toward the top.

3. What is the difference between relative and absolute age?
Relative age is the age of a rock layer (or the fossils it contains) compared to other layers. It can be determined by looking at the position of rock layers. Absolute age is the numeric age of a layer of rocks or fossils. Absolute age can be determined by using radiometric dating.

4. Look at the diagram below and then answer this question:
We can date the layers of volcanic ash using radiometric dating, but how can we determine the absolute age of fossil A?

You have to date the volcanic layer above and below the fossil layer. The age of the fossil will be an age range between the ages of the two volcanic layers.

5. The diagram below shows a portion of the Geologic Time Scale. What do the divisions of time represent?
b) major changes in flora (plants) and fauna (animals)