Time Scales Time Perspectives Chronostratigraphy Geologic Time Scale Radioactive Decay Radiometric...

Time Scales

• Time Perspectives

• Chronostratigraphy

• Geologic Time Scale

• Radioactive Decay

• Radiometric Dating

• Pilot Knob Lab

Text: Manual, p. 3, 29, 131-136; Boggs, Ch. 18

Catastrophism

Time Perspectives

http://www.meteorcrater.com/

Uniformitarianism

Time Perspectives

Time Perspectives

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? how may years to save 1 billion $

How Much is a Billion?

Time Scales

The Geologic Time Scale: an arrangement of the earth’s geologic record into a standard sequence of units.

• relative age order

• boundaries based on fossils, lithology, polarity

• absolute ages by radiometric dating

Time Scales

• Time Perspectives

• Chronostratigraphy

• Geologic Time Scale

• Radioactive Decay

• Radiometric Dating

• Pilot Knob Lab

Text: Manual, p. 3, 29, 131-136; Boggs, Ch. 18

Chronostratigraphy

Chronostratigraphy: establish time relationships among rock units

Geologic Time Units

• Geochronologic Units - time interval

• Chronostratigraphic Units - rock body representative of time interval

Chronostratigraphy

Eon

Era

*Period

Epoch

Age

Chron

Geochronologic Unit – time interval

Chronostratigraphy

Eon – Phanerozoic

Era – Mesozoic

*Period – Cretaceous

Epoch – Late Cretaceous

Age – Campanian

Chron – Orbitoides tissoti

Geochronologic Unit – time interval

Chronostratigraphy

Eonothem

Erathem

*System

Series

Stage

Chronozone

Chronostratigraphic Unit – rock bodies representative of time interval

Chronostratigraphy

Eonothem

Erathem

*System – Cretaceous System

Series – Upper Cretaceous Series

Stage

Chronozone

Chronostratigraphic Unit – rock bodies representative of time interval

Chronostratigraphy

System Subdivisions

Lower and Upper

Period Subdivisions

Early and Late

Time Scales

• Time Perspectives

• Chronostratigraphy

• Geologic Time Scale

• Radioactive Decay

• Radiometric Dating

• Pilot Knob Lab

Text: Manual, p. 3, 29, 131-136; Boggs, Ch. 18

Geologic Time Scale

(Harland et al., 1990)

Ryazanian

Maastrichtian

Campanian

Cenomanian

Coniacian

Turonian

Santonian

Albian

Barremain

Aptian

Hauterivian

ValanginianA

ge

s o

f C

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ceo

us

Pe

rio

d

Even More Detail…

Geologic Time Scale

after (http://www.ucmp.berkeley.edu/precambrian/precambrian.html)

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Precambrian Events

World’s Oldest Rocks (Age in Billion Years)

4.0

3.8

3.5-3.7

3.5

3.6

4.4

Geologic Time Scale

after (http://www.ucmp.berkeley.edu/precambrian/precambrian.html)

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www.calm.wa.gov.au/national_parks/hamelin_pool_mnr.html

Geologic Time Scale

Precambrian Events

after (http://www.ucmp.berkeley.edu/precambrian/precambrian.html)

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http://www-rohan.sdsu.edu/~rhmiller/depositionfeatures1/

Geologic Time Scale

Precambrian Events

after (http://www.ucmp.berkeley.edu/precambrian/precambrian.html)

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http://www.ucmp.berkeley.edu/vendian/pter.gif

Geologic Time Scale

Precambrian Events

http://www.inhandmuseum.com/images/Geologic_Timeline.GIF

http://palaeo.gly.bris.ac.uk/Palaeofiles/Lagerstatten/Burgess/gallery.html

Amphibians

Animals with Hard Parts

Land Plants

Geologic Time Scale

http://www.inhandmuseum.com/images/Geologic_Timeline.GIF

Primates

Break-up of Pangea

Amphibians

Animals with Hard Parts

Land Plants

Dinosaurs

http://www.inhandmuseum.com/images/Geologic_Timeline.GIF

PrimatesGrasses

Human Civilizations

Ice Ages

Break-up of Pangea

Amphibians

Animals with Hard Parts

Land Plants

Dinosaurs

Relative Time Absolute Ages

Time Scales

• Time Perspectives

• Chronostratigraphy

• Geologic Time Scale

• Radioactive Decay

• Radiometric Dating

• Pilot Knob Lab

Text: Manual, p. 3, 29, 131-136; Boggs, Ch. 18

Radioactive Decay

Daughter

• loss of particle from nucleus

• statistical behavior of population

• constant decay rate

Parent

radioactive radiogenic

Alphapa.movBetapar.mov

Radioactive Decay

Alpha Decay: lose 2P + 2 N

Beta Decay: N P and lose e-

Some Types of Radioactive Decay

AGI, 1999

87Rb 87Sr

Radioactive Decay

Time Atoms Parent Atoms Daughter

“Close the Box” 6 0

1 Half Life 3 3

Radioactive Decay

“Close the Box”

Half Life: The time required for half of the amount of parent to decay to daughter

Nu

mb

er

of

Pa

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Number of Half Lives

0 1 2 3 4

100

80

60

40

20

0

Radioactive Decay

M&M Experiment

Radioactive Decay

Time Scales

• Time Perspectives

• Chronostratigraphy

• Geologic Time Scale

• Radioactive Decay

• Radiometric Dating

• Pilot Knob Lab

Text: Manual, p. 3, 29, 131-136; Boggs, Ch. 18

Parent-Daughter Pairs

Parent Daughter Half-Life (y) Age Ranges Material 238U 206Pb 4.5 billion < 65 million zircon235U 207Pb 704 million > 60 million zircon

87Rb 87Sr 49 billion > 5 million micas, K-spar40K 40Ar 1.3 billion > 100,000 micas14C 14N 5,730 < 40,000 organics, calcite

Radiometric Dating

measure amount of parent and daughter

isolate parent and daughter

Radiometric Dating

Analytical Methods

What event are you dating?

Radiometric Dating

volcano2_und_nodak_edu

NPS

zircon

• choose right mineral

• assume a closed system

Radiometric Dating

Considerations

14C-dating Concerns

variable production rates of 14C

old C in oceans

selective uptake of 14C

Radiometric Dating

Calibrate the Time Scale

absolute date

absolute date

relative age biozone

relative age biozone

Radiometric Dating

http://www.talkorigins.org/faqs/dating.html

Radiometric Dating

Assign ages to relative time period boundaries

USGS

Time Scales

• Time Perspectives

• Chronostratigraphy

• Geologic Time Scale

• Radioactive Decay

• Radiometric Dating

• Pilot Knob Lab

Text: Manual, p. 3, 29, 131-136; Boggs, Ch. 18

Pilot Knob Lab

• basalt

• pyroclastics

Pilot Knob Lab

Pilot Knob Lab

Kavachi, Solomon Islands

NOOA