1. Aim: How do we determine the relative age of rock strata? Do Now: Clear your desk except for your Earth Science Reference Table

2. Fossil Dating

3. HOW DO WE KNOW THE AGE OF FOSSILS? -Scientists use 2 methods to determine the age of fossils: 1. Relative Dating 2. Absolute Dating

4. Relative Dating Shows the order in which fossils occurred- does not give exact ages. Shows what organisms lived together. Scientists look at where fossils are located within the rock column. Use the Law of Superposition

5. Law of Superposition Sedimentary layers are deposited in a time sequence Oldest rock on the bottom, youngest at the top Youngest Oldest

6. Absolute Dating Determines the specific age of a fossil Looks at chemical properties 2 types: –Carbon-14 (radiocarbon) –Potassium-Argon

7. Carbon-14 Dating Also known as Radiocarbon dating Used to date organic substances Scientists measure the radiocarbon in the fossil to determine its age Can only date specimens up to about 60,000 years old

8. Potassium-Argon Dating Scientists determine the age of the rock surrounding the fossil to determine the fossil’s age. Used only for inorganic substances (rocks and minerals) Scientists measure the amount of argon in the rock to determine its age Dates rock 60,000 years old and older

9. QUIZ

10. Which rock layer is the oldest? Youngest? Oldes t Youngest

11. If you wanted to figure out the exact age of a rock, what technique would you use? a.Relative Dating b.Carbon-14 Dating c.Law of Superposition d.Potassium-Argon Dating

12. If you were looking to find the exact age of a fossil that is at least 1 million years old, what technique would you use? a. Carbon-14 Dating b. Potassium-Argon Dating c. Relative Dating d. You can’t; it is impossible

13. If you wanted to figure out the exact age of a fossil that is less than 40,000 years old, what technique would you use? a. Carbon-14 Dating b. Potassium-Argon Dating c. Relative Dating d. You can’t; it is impossible

14. List the teachers from oldest to youngest? Walsh Antonecchia Adamiak Mr. Mulvey Abrahamson Pimentel Lanese Turnbull Scherer Heckman

15. How do we define relative age? Original Horizontality: rocks deposited in horizontal layers D, K, A, G Relative age (dating): age of rocks or events compared to the surrounding rocks/events Law of Superposition: Oldest layer on the bottom and youngest layer on top. –Undisturbed rocks Uniformitarianism: The present is the key to the past.

16. How does the following events affect the rocks? Law of Cross - Cutting Relationships Folds,FaultsTilting,Overturn folds,

17. How are the following cross cutting relationships younger? Intrusions – (igneous) younger than rocks that surround it. –Contact metamorphism on all sides Extrusions – (igneous) Are always YOUNGER than the rocks they sit on. (Lava solidifying on the surface after an eruption.) –contact metamorphism only with rocks below If the lines (contact metamorphism) touch the rock layer, then the rock layer is older than the intrusion.

18. How do we define unconformity? Unconformity – buried erosional surface represents a gap(missing time) in the geologic rock record Erosional Agent Unconformity

19. Extra Questions Identify the letter of the rock unit that is the youngest event. Rock unit C is younger because there is contact metamorphism with the bottom rock layer D.