1. An introduction Geologic Time

2. Which elephant is older????

3. Oldest Youngest

4. These two questions are related to relative time versus absolute ages. Relative time: Which elephant is oldest? Youngest? Absolute age: How old is the oldest elephant? Youngest? oldest youngest Born in 1970 Born in 1999

5. Rocks Record Earth’s History Rocks record geological events and changing life forms of the past We have learned that Earth is much older than anyone had previously imagined and that its surface and interior have been changed by the same geological processes that continue today.

6. The same two questions are frequently asked in the geosciences. Relative time: Which rock unit is oldest? Youngest Absolute age: How old is the oldest rock unit? Youngest ? older younger 975 Ma 375 Ma I made these dates up!

7. Three terms Strata-layers of rock Stratigraphy- science of studying, describing, and correlating strata Stratigraphic Column- An ordered sequence of strata.

9. Discovering Earth’s History Uniformitarianism means that the forces and processes that we observe today have been at work for a very long time.

10. Law of Superposition In an undisturbed rock sequence, younger rocks are found on top of older rocks.

13. Unconformity An unconformity represents a long period during which deposition stopped, erosion removed previously formed rocks, and then deposition resumed.

15. Principle of Cross-Cutting Relationships The principle of cross-cutting relationships states that when a fault cuts through rock layers, or when magma intrudes other rocks and crystallizes, we can assume that the fault or intrusion is younger than the rocks affected.

16. Principle of Cross-Cutting Relationships

17. Another Example Oldest to Youngest 1,2,3,4,5