1. Geologic Time
Rocks record geologic events and the changing life forms of the past.
Uniformitarianism: The forces and processes that we observe today have been at work for a very long time.

2. Relative Dating
Tells us the sequence (order) in which events occurred, but NOT HOW LONG AGO they occurred.

3. Relative Dating
*3 Laws/Principles: 1. Law of Superposition: In an undisturbed sequence of sedimentary rocks, each bed is older than the one above it and younger than the one below it.

4. Stratigraphy

5. Relative Dating
2. Principle of Original Horizontality: Layers of sediment are generally deposited in a horizontal position.

7. Relative Dating
3. Principle of Cross-Cutting Relationships: States that when a fault cuts through or when magma intrudes into other rocks and crystallizes, we can assume that the fault or intrusion is younger than the rocks affected.

8. Relative Dating
Inclusion: Pieces of rock units that are contained within another (are younger than the rock they are in).

9. Relative Dating
Unconformity: a gap in the geologic record that occurs when rock is eroded, exposing older rock and then new rock forms on the much older exposed rock.

10. Absolute Dating Three Types: Radiometric Dating Tree Ring Dating
Ice Core Dating

11. Radiometric Dating
Radiometric Dating: Calculating the age of rocks and minerals that contain certain radioactive isotopes.
Uses the half-lives of those isotopes to calculate the age of rocks.

12. Radiometric Dating
Half-Life: The time it takes for 50% (1/2) of the nuclei in a radioactive sample to decay to its stable isotope.
Multiply the number of half-lives by the half-life time to get the age of a fossil.

14. Half-Life Practice
A bone of a T-Rex contains 1/16 the original parent material. Haw many half-lives have occurred in the T-Rex bone?
If 2 half lives have passed, what fraction of the original parent material remains?
If the half-life time of an isotope is 10,000 years and 3 half lives have passed, what is the age of the fossil?

15. Radiometric Dating
This method is possible because each radioactive isotope decays at a CONSTANT rate.
Cannot be used for sedimentary rocks because they are formed from many pieces of older rocks, so there would be many ages of rocks.

16. Tree Ring Dating Tree rings are a glimpse into the past.
Width of bands indicate climate changes and number of rings indicate age.
Must use a sample to be sure the results are accurate.

17. Ice Core Dating
Each layer of ice in a core corresponds to a single year, or sometimes even a single season and most everything that fell in the snow that year remains behind, including wind-blown dust, ash, atmospheric gases and even radioactivity.

18. Ice Core Dating