Relative Age Dating Vs. Exact Age Dating

Relative Age Dating Vs. Exact Age Dating

How do geologists know how old something is?

How old is the earth?

How do geologists know how old something is?

How old is the earth?

Relative Age DatingRelative Age Dating

WITHOUT TALKING!With the students in your rowLine up from youngest to oldestWITHOUT TALKING!You have 5 minWITHOUT TALKING!

WITHOUT TALKING!With the students in your rowLine up from youngest to oldestWITHOUT TALKING!You have 5 minWITHOUT TALKING!

Relative Age DatingRelative Age Dating

Analyze: 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.

Analyze: 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.

Relative Dating Laws review

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.

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.

Law of original horizontality

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.

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.

Law of lateral continuityLaw of lateral continuityLayers

continue until they reach an edge or run out.

Layers continue until they reach an edge or run out.

Relative Play DoughRelative Play Dough

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Relative dating practice problem #1

Relative dating practice problem #1 B-superposition

A-cross cutting C-superposition D- superposition K-original

horizontality L- cross cutting J- superposition/lateral

continuity Folding - original

horizontality I- superposition H- superposition G- superposition F- superposition E- superposition

B-superposition A-cross cutting C-superposition D- superposition K-original

horizontality L- cross cutting J- superposition/lateral

continuity Folding - original

horizontality I- superposition H- superposition G- superposition F- superposition E- superposition

Relative dating practice #2

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- 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-superpositionTilt may have occurred

before N & L or after.

Exact Age DatingExact 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.

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.

Radioactive DecayRadioactive 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.

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.

Radioactive DecayRadioactive DecayDifferent elements have different

decay ratesMust 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.

Different elements have different decay rates

Must use different elements for different ages of rocks

Limitations: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.

Elements for Radiometric Dating

Elements for Radiometric Dating

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How do they do it?How do they do it?Radiometric dating process.Radiometric dating process.

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