telling time geologically determining numerical or absolute age factors affecting isotopic dating...

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Page 1: TELLING TIME GEOLOGICALLY DETERMINING NUMERICAL OR ABSOLUTE AGE FACTORS AFFECTING ISOTOPIC DATING Most useful in igneous rocks. As minerals crystallize,
Page 2: TELLING TIME GEOLOGICALLY DETERMINING NUMERICAL OR ABSOLUTE AGE FACTORS AFFECTING ISOTOPIC DATING Most useful in igneous rocks. As minerals crystallize,

TELLING TIME GEOLOGICALLY

DETERMINING NUMERICAL OR ABSOLUTE AGE

FACTORS AFFECTING ISOTOPIC DATING

Most useful in igneous rocks.As minerals crystallize, radioactive isotopes become

incorporated in the minerals.No daughter isotopes at that time.Crystallization sets the isotopic “clock”.

Doesn’t work in sedimentary rocks. How come?

Page 3: TELLING TIME GEOLOGICALLY DETERMINING NUMERICAL OR ABSOLUTE AGE FACTORS AFFECTING ISOTOPIC DATING Most useful in igneous rocks. As minerals crystallize,

TELLING TIME GEOLOGICALLY

DETERMINING NUMERICAL OR ABSOLUTE AGE

FACTORS AFFECTING ISOTOPIC DATING

Works best when a rock or mineral represents a “closed” system.

Parent and daughter isotopes cannot move in or out ofa mineral or rock.

Igneous rocks best fit this criteria.

Page 4: TELLING TIME GEOLOGICALLY DETERMINING NUMERICAL OR ABSOLUTE AGE FACTORS AFFECTING ISOTOPIC DATING Most useful in igneous rocks. As minerals crystallize,

TELLING TIME GEOLOGICALLY

DETERMINING NUMERICAL OR ABSOLUTE AGE

FACTORS AFFECTING ISOTOPIC DATING

Metamorphic rocks are not always closed systems.During metamorphism, heat, pressure, and circulating

fluids affect mineral grains.Daughter isotopes are generally lost in the process.

Dating metamorphic rocks provides the age of the metamorphic event rather than the age of therocks themselves.

Page 5: TELLING TIME GEOLOGICALLY DETERMINING NUMERICAL OR ABSOLUTE AGE FACTORS AFFECTING ISOTOPIC DATING Most useful in igneous rocks. As minerals crystallize,

TELLING TIME GEOLOGICALLY

DETERMINING NUMERICAL OR ABSOLUTE AGE

FACTORS AFFECTING ISOTOPIC DATING

Accuracy of isotope dating also depends on the condition of the material dated

Fractured or weathered rock is not a good candidate.

Age of the rocks being considered also presents someproblems.

Very young rocks may not have had enough time toaccumulate enough daughter isotope to measure.

Need to choose a radioactive isotope with t½ that fits theapproximate age of the rock.

Page 6: TELLING TIME GEOLOGICALLY DETERMINING NUMERICAL OR ABSOLUTE AGE FACTORS AFFECTING ISOTOPIC DATING Most useful in igneous rocks. As minerals crystallize,

TELLING TIME GEOLOGICALLY

DETERMINING NUMERICAL OR ABSOLUTE AGE

FACTORS AFFECTING ISOTOPIC DATING

The minerals in the rock also determine which isotopethat is best for dating the rock.

Page 7: TELLING TIME GEOLOGICALLY DETERMINING NUMERICAL OR ABSOLUTE AGE FACTORS AFFECTING ISOTOPIC DATING Most useful in igneous rocks. As minerals crystallize,

TELLING TIME GEOLOGICALLY

DETERMINING NUMERICAL OR ABSOLUTE AGE

TYPES OF ISOTOPIC DATING TECHNIQUES

Uranium (U) - Thorium (Th) - Lead (Pb) Dating

238U decays to 206Pb235U decays to 207Pb232Th decays to 208Pb

Rocks containing Uranium provide three possibletechniques.

Because all three occur together, it allows a methodto cross-check the dates.

Page 8: TELLING TIME GEOLOGICALLY DETERMINING NUMERICAL OR ABSOLUTE AGE FACTORS AFFECTING ISOTOPIC DATING Most useful in igneous rocks. As minerals crystallize,

TELLING TIME GEOLOGICALLY

DETERMINING NUMERICAL OR ABSOLUTE AGE

TYPES OF ISOTOPIC DATING TECHNIQUES

Uranium (U) - Thorium (Th) - Lead (Pb) Dating238U decays to 206Pb

Page 9: TELLING TIME GEOLOGICALLY DETERMINING NUMERICAL OR ABSOLUTE AGE FACTORS AFFECTING ISOTOPIC DATING Most useful in igneous rocks. As minerals crystallize,
Page 10: TELLING TIME GEOLOGICALLY DETERMINING NUMERICAL OR ABSOLUTE AGE FACTORS AFFECTING ISOTOPIC DATING Most useful in igneous rocks. As minerals crystallize,

TELLING TIME GEOLOGICALLY

DETERMINING NUMERICAL OR ABSOLUTE AGE

TYPES OF ISOTOPIC DATING TECHNIQUES

Uranium (U) - Thorium (Th) - Lead (Pb) Dating238U decays to 206Pb

Half-life (t1/2) is 4.5 billion years.

Can be applied to igneous and metamorphic rocks.

Uses zircons, uraninite and uranium ores.

Page 11: TELLING TIME GEOLOGICALLY DETERMINING NUMERICAL OR ABSOLUTE AGE FACTORS AFFECTING ISOTOPIC DATING Most useful in igneous rocks. As minerals crystallize,

TELLING TIME GEOLOGICALLY

DETERMINING NUMERICAL OR ABSOLUTE AGE

TYPES OF ISOTOPIC DATING TECHNIQUES

Uranium (U) - Thorium (Th) - Lead (Pb) Dating235U decays to 207Pb

Half-life (t1/2) is 713 million years.

Can be applied to igneous and metamorphic rocks.

Uses zircons, uraninite and uranium ores.

Page 12: TELLING TIME GEOLOGICALLY DETERMINING NUMERICAL OR ABSOLUTE AGE FACTORS AFFECTING ISOTOPIC DATING Most useful in igneous rocks. As minerals crystallize,

TELLING TIME GEOLOGICALLY

DETERMINING NUMERICAL OR ABSOLUTE AGE

TYPES OF ISOTOPIC DATING TECHNIQUES

Uranium (U) - Thorium (Th) - Lead (Pb) Dating232Th decays to 208Pb

Half-life (t1/2) is 14.1 billion years.

Can be applied to igneous and metamorphic rocks.

Uses zircons, uraninite and uranium ores.

Page 13: TELLING TIME GEOLOGICALLY DETERMINING NUMERICAL OR ABSOLUTE AGE FACTORS AFFECTING ISOTOPIC DATING Most useful in igneous rocks. As minerals crystallize,

TELLING TIME GEOLOGICALLY

DETERMINING NUMERICAL OR ABSOLUTE AGE

TYPES OF ISOTOPIC DATING TECHNIQUES

Potassium (K) - Argon (Ar) Dating

Potassium (K) is an extremely common element.One isotope, 40K, is radioactive.Found in muscovite, biotite, orthoclase and glauconite.Used to date volcanic rocks.

Page 14: TELLING TIME GEOLOGICALLY DETERMINING NUMERICAL OR ABSOLUTE AGE FACTORS AFFECTING ISOTOPIC DATING Most useful in igneous rocks. As minerals crystallize,

TELLING TIME GEOLOGICALLY

DETERMINING NUMERICAL OR ABSOLUTE AGE

TYPES OF ISOTOPIC DATING TECHNIQUES

Potassium (K) - Argon (Ar) Dating

Produced by electron or beta () capture.

Half-life (t1/2) is 1.3 billion years.Range is 100,000 to 4.6 billion years.Useful for relatively young and very old rocks.

Page 15: TELLING TIME GEOLOGICALLY DETERMINING NUMERICAL OR ABSOLUTE AGE FACTORS AFFECTING ISOTOPIC DATING Most useful in igneous rocks. As minerals crystallize,

TELLING TIME GEOLOGICALLY

DETERMINING NUMERICAL OR ABSOLUTE AGE

TYPES OF ISOTOPIC DATING TECHNIQUES

Potassium (K) - Argon (Ar) Dating

Problem with K-Ar dating is that the Argon producedis a gas and with fracturing, weathering, ormetamorphism, the gas can be lost, resettingthe clock.

Page 16: TELLING TIME GEOLOGICALLY DETERMINING NUMERICAL OR ABSOLUTE AGE FACTORS AFFECTING ISOTOPIC DATING Most useful in igneous rocks. As minerals crystallize,

TELLING TIME GEOLOGICALLY

DETERMINING NUMERICAL OR ABSOLUTE AGE

TYPES OF ISOTOPIC DATING TECHNIQUES

Rubidium (Rb) - Strontium (Sr) Dating

Rubidium (Rb) decays to Strontium (Sr).

Half-life (t1/2) is 47 billion years.

Found in muscovite, biotite, feldspars and hornblende.Used to date volcanic and metamorphic rocks.Because of large half-life, rocks between 10 million and

4.6 billion years can be dated.

Page 17: TELLING TIME GEOLOGICALLY DETERMINING NUMERICAL OR ABSOLUTE AGE FACTORS AFFECTING ISOTOPIC DATING Most useful in igneous rocks. As minerals crystallize,

TELLING TIME GEOLOGICALLY

DETERMINING NUMERICAL OR ABSOLUTE AGE

TYPES OF ISOTOPIC DATING TECHNIQUES

14Carbon (C) Dating

Produced by Beta () decay.

Half-life (t1/2) is 5,730 years.

Age range is 100 to 70,000 (really ~50,000) years.Used to date carbon-based remains like bones, plant

remains (wood, pollen, seeds), shells, cloth, paperand charcoal.

Page 18: TELLING TIME GEOLOGICALLY DETERMINING NUMERICAL OR ABSOLUTE AGE FACTORS AFFECTING ISOTOPIC DATING Most useful in igneous rocks. As minerals crystallize,

TELLING TIME GEOLOGICALLY

DETERMINING NUMERICAL OR ABSOLUTE AGE

TYPES OF ISOTOPIC DATING TECHNIQUES

14Carbon (C) Dating14C is produced in the

atmosphere.Cosmic rays hit other atoms in

atmosphere, giving offneutrons.

Neutrons hit 14N and decayoccurs producing 14C.

Page 19: TELLING TIME GEOLOGICALLY DETERMINING NUMERICAL OR ABSOLUTE AGE FACTORS AFFECTING ISOTOPIC DATING Most useful in igneous rocks. As minerals crystallize,

14C in atmosphere combines with O2 to produce 14CO2.Plants and animals ingest or breathe in 14CO2 and it

becomes incorporated in the organism.Upon death, 14C decays back into 14N.

The rate of cosmic ray bombardment has varied overtime.

Needs to be calibrated with other techniques.

TELLING TIME GEOLOGICALLY

DETERMINING NUMERICAL OR ABSOLUTE AGE

TYPES OF ISOTOPIC DATING TECHNIQUES

14Carbon (C) Dating

Page 20: TELLING TIME GEOLOGICALLY DETERMINING NUMERICAL OR ABSOLUTE AGE FACTORS AFFECTING ISOTOPIC DATING Most useful in igneous rocks. As minerals crystallize,

FISSION is the division of radioactive nuclei into twoequally-sized fragments.

Process releases and particles.When splitting occurs, particles rip through the mineral

lattice (crystal structure) producing tracks or tears in the lattice.

Occurs continuously in minerals with radioactive substances.

TELLING TIME GEOLOGICALLY

DETERMINING NUMERICAL OR ABSOLUTE AGE

OTHER NUMERICAL DATING TECHNIQUES

FISSION-TRACK DATING

Page 21: TELLING TIME GEOLOGICALLY DETERMINING NUMERICAL OR ABSOLUTE AGE FACTORS AFFECTING ISOTOPIC DATING Most useful in igneous rocks. As minerals crystallize,

The older the mineral, the more tracks are produced.Age range is 50,000 to billions of years.Can be applied to volcanic glass, zircons and apatites.

Limitations do exist.Temperatures above 250C cause tracks to heal.Can’t be used to date medium- to high-grade

metamorphic rocks.Fills the gap between 14C and K-Ar techniques.

TELLING TIME GEOLOGICALLY

DETERMINING NUMERICAL OR ABSOLUTE AGE

OTHER NUMERICAL DATING TECHNIQUES

FISSION-TRACK DATING

Page 22: TELLING TIME GEOLOGICALLY DETERMINING NUMERICAL OR ABSOLUTE AGE FACTORS AFFECTING ISOTOPIC DATING Most useful in igneous rocks. As minerals crystallize,

TELLING TIME GEOLOGICALLY

DETERMINING NUMERICAL OR ABSOLUTE AGE

OTHER NUMERICAL DATING TECHNIQUES

FISSION-TRACK DATING

13.5 m

1 m = 0.001 mm

Page 23: TELLING TIME GEOLOGICALLY DETERMINING NUMERICAL OR ABSOLUTE AGE FACTORS AFFECTING ISOTOPIC DATING Most useful in igneous rocks. As minerals crystallize,

Trees in temperate regions produce light and dark annual growth rings.

By counting the rings, the tree’s age can be determined.

TELLING TIME GEOLOGICALLY

DETERMINING NUMERICAL OR ABSOLUTE AGE

OTHER NUMERICAL DATING TECHNIQUES

DENDROCHRONOLOGY

Page 24: TELLING TIME GEOLOGICALLY DETERMINING NUMERICAL OR ABSOLUTE AGE FACTORS AFFECTING ISOTOPIC DATING Most useful in igneous rocks. As minerals crystallize,

Climate and other events arealso recorded.

By comparing the ring countsand chronology fromliving and fossil treesa dendrochronology fora region can be formed.

Goes back about 9000 years.

TELLING TIME GEOLOGICALLY

DETERMINING NUMERICAL OR ABSOLUTE AGE

OTHER NUMERICAL DATING TECHNIQUES

DENDROCHRONOLOGY

Page 25: TELLING TIME GEOLOGICALLY DETERMINING NUMERICAL OR ABSOLUTE AGE FACTORS AFFECTING ISOTOPIC DATING Most useful in igneous rocks. As minerals crystallize,

TELLING TIME GEOLOGICALLY

DETERMINING NUMERICAL OR ABSOLUTE AGE

OTHER NUMERICAL DATING TECHNIQUES

VARVE CHRONOLOGY

Lakes can produce annual layers.Usually occur in glacial lakes or those that freeze

over in winter.Coarser sediments are deposited in summer.Winter-summer layers are called COUPLETS.Couplets in lakes are known as VARVES.Count the couplets back from the sediment surface

to determine numerical age.

Page 26: TELLING TIME GEOLOGICALLY DETERMINING NUMERICAL OR ABSOLUTE AGE FACTORS AFFECTING ISOTOPIC DATING Most useful in igneous rocks. As minerals crystallize,

TELLING TIME GEOLOGICALLY

DETERMINING NUMERICAL OR ABSOLUTE AGE

OTHER NUMERICAL DATING TECHNIQUES

VARVE CHRONOLOGY

Page 27: TELLING TIME GEOLOGICALLY DETERMINING NUMERICAL OR ABSOLUTE AGE FACTORS AFFECTING ISOTOPIC DATING Most useful in igneous rocks. As minerals crystallize,

TELLING TIME GEOLOGICALLY

DETERMINING NUMERICAL OR ABSOLUTE AGE

OTHER NUMERICAL DATING TECHNIQUES

LICHENOMETRY

Lichens are plant-like organismsthat grow on rocks.

Grow at a measurable rate.By measuring size on items of

known date, the size isplotted against size on unknown aged objects.

Good for the last 9000 years.

Page 28: TELLING TIME GEOLOGICALLY DETERMINING NUMERICAL OR ABSOLUTE AGE FACTORS AFFECTING ISOTOPIC DATING Most useful in igneous rocks. As minerals crystallize,

TELLING TIME GEOLOGICALLY

DETERMINING NUMERICAL OR ABSOLUTE AGE

OTHER NUMERICAL DATING TECHNIQUES

LICHENOMETRY