relative age dating vs. exact age dating how do geologists know how old something is? how old is the...
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Relative Age Dating Vs. Exact Age Dating
How do geologists know how old something is?
How old is the earth?
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Relative Age Dating
WITHOUT TALKING!With the students in your rowLine up from youngest to oldest
WITHOUT TALKING!You have 5 minWITHOUT TALKING!
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Relative Age Dating
Analyze: Determine your group’s accuracy. (You can talk now! Don’t move yet!) How accurate were you?Exact! (tumb up)Nearly. (thumb sideways)Yikes! Not at all.(thumb down)
EXACT AGE DATING: 2nd attempt, talking allowed, fix the age line up.
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Relative Dating Laws review
1. Law of superposition2. Law of original horizontality3. Law of lateral continuity4. Principle of cross cutting
relationships.5. Principle of fossil
succession/correlation All of these give us relative ages.
This rock is older than that one, but younger than this other one.
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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.
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Law of lateral continuityLayers
continue until they reach an edge or run out.
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Fossil Correlation
Rocks containing the same index fossils are the same age.
Fossils must be: widespread, develop and go extinct quickly, & cannot be tied to a type of rock.
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Relative Play Dough
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Relative dating practice problem #1 B-superposition
A-cross cutting C-superposition D- superposition K-original
horizontality L- cross cutting Folding - original
horizontality J-
superposition/lateral continuity
I- superposition H- superposition G- superposition F- superposition E- superposition
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Relative dating practice #2 Tilt- original horizontality
F, H, K, A, Q- (in order) superposition
Tilt? And erosion-original horizontality
L-cross cutting N-cross cutting M-superposition J-superposition I-superposition Erosion of C/B B-cross cutting E/G?-Cross cutting C-superposition D-superposition
Tilt may have occurred before N & L or after.
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Exact Age DatingMeasurable! 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.
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Radioactive DecayFor example,
uranium decays into lead.
A sample starts off with all uranium and no lead.
Over time, the ratio of lead to uranium increases.
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Radioactive DecayDifferent elements have different
decay ratesMust use different elements for
different ages of rocksLimitations:
Presence of radioactive isotopes (igneous rock most common)
Age of rock (too young/old for the isotope present)
Sedimentary rock is made up of sediments or pieces of other rock. (not accurate)
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Elements for Radiometric Dating
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How do they do it?Radiometric dating process.