1. Jump to first page Geologic Time Chapter 34

2. Jump to first page Dating rocks n Relative dating F Compare events and put them in order based on their sequence of formation, oldest to youngest. n Absolute dating F Using radioactive decay to determine the exact age of rocks

3. Jump to first page The Geologic Time Scale p. 182 Cenozoic Mesozoic Paleozoic Precambrian Phanerozoic

4. Jump to first page Geologic Time Scale n Geologists have divided the earth’s history into various eras, periods and epochs using fossil evidence (which life forms lived when) n The chart has been updated many times as more fossil evidence is located

5. Jump to first page Principles of relative dating Principles of relative dating n Law of superposition F In an undisturbed sequence of sedimentary rocks the oldest rocks are on the bottom, youngest on top

6. Jump to first page Law of superposition

7. Jump to first page Principles of relative dating Principles of relative dating n Principle of original horizontality F Layers of sediment are generally deposited in a horizontal, flat-lying position F Rock layers that are flat have not been disturbed

8. Jump to first page Principles of relative dating Principles of relative dating n Principle of cross-cutting relationships F Younger features cut across older feature F A fault or dike that cuts across sedimentary layers is younger than the layers. Igneous dikes cutting across metamorphic rock

9. Jump to first page Principles of relative dating n Included Fragments F An inclusion is a piece of rock that is enclosed within another rock (2 examples: xenolith and pebble in conglomerate) F Rock containing the inclusion is younger, the inclusion is older

10. Jump to first page Principles of relative dating n Unconformity F An unconformity is a break in the rock record produced by erosion and/or nondeposition of rock layers

11. Jump to first page Sketch of an unconformity:

12. Jump to first page Geological events of an unconformity: 1. Sedimentation / deposition and lithification 2. Deformation / folding and erosion 3. Subsidence, water is covering 4. More sedimentation happened once covered with water

13. Jump to first page Unconformity in rocks: Angular unconformity at Siccar Point, Scotland