1. Relative Age The relative age of rocks refers to the order in which they occurred When something is dated in a relative manner, we can say “This layer of rock is older than this layer” We cannot say “This layer of rock is 5000000 years old

2. Principle of original horizontality Original Horizontality: sedimentary layers are initially deposited in horizontal layers

3. Law of Superposition Older layers are found towards the bottom in a series of layers. Younger layers are found towards the top.

5. Crosscutting Rule Any event that disturbs a rock is always more recent (younger) than the rock itself. Clearly, the rock must be in place before something can happen to it.

7. Geological Detective Work Two trees have fallen in the forest. How could you find out which occurred first? Law of superposition (if one fell on the other) snowfall moss buildup decay

8. When volcanoes erupt, they can leave a layer of ash over thousands of miles. This layer can be used to help date deposits in a relative manner. See Figure 12.13 on p. 265

9. Which Came First? W J C - fracture E L

10. Which Came First? S B G K H M - fracture R - folding