Presentation on theme: "Relative Age Dating Vs. Exact Age Dating"— Presentation transcript:
1 Relative Age Dating Vs. Exact Age Dating How do geologists know how old something is?How old is the earth?
2 Relative Age Dating WITHOUT TALKING! With the students in your row Line up from youngest to oldestYou have 5 min
3 Relative Age DatingAnalyze: Without moving, determine your group’s accuracy. (You can talk now!) How accurate were you?Exact!Nearly.Yikes! Not at all.EXACT AGE DATING: 2nd attempt, talking allowed, fix the age line up.
4 Relative Dating Laws review Law of superpositionLaw of original horizontalityLaw of lateral continuityPrinciple of cross cutting relationships.Principle of fossil succession/correlationAll of these give us relative ages.This rock is older than that one, but younger than this other one.
5 Law of original horizontality Layers have to be formed before anything can be done to them. Any layer that has folds, tilts, or erosion can use this law to help date it.
6 Law of lateral continuity Layers continue until they reach an edge or run out.
8 Relative dating practice problem #1 B-superpositionA-cross cuttingC-superpositionD- superpositionK-original horizontalityL- cross cuttingJ- superposition/lateral continuityFolding - original horizontalityI- superpositionH- superpositionG- superpositionF- superpositionE- superposition
9 Relative dating practice #2 Tilt- original horizontalityF, H, K, A, Q- (in order) superpositionTilt? And erosion-original horizontalityL-cross cuttingN-cross cuttingM-superpositionJ-superpositionI-superpositionErosion of C/BB-cross cuttingE/G?-Cross cuttingC-superpositionD-superpositionTilt may have occurred before N & L or after.
10 Exact Age Dating Measurable! Like lining up by height. Radiometric DatingUses radioactive isotopes and decay rates to determine exact ages of rocks and fossils.Half life- the amount of time it takes for one half of a radioactive isotope to decay.
11 Radioactive Decay For example, uranium decays into lead. A sample starts off with all uranium and no lead.Over time, the ratio of lead to uranium increases.
12 Radioactive Decay Different elements have different decay rates Must use different elements for different ages of rocksLimitations:Presence of radioactive isotopes (some types of rocks don’t have any)Age of rock (too young/old for the isotope present)Sedimentary rock is made up of sediments or pieces of other rock.