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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
save $100 / day
? 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
reta
ceo
us
Pe
rio
d
Even More Detail…
Geologic Time Scale
after (http://www.ucmp.berkeley.edu/precambrian/precambrian.html)
mil
lio
ns
of
year
s ag
oGeologic Time Scale
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)
mil
lio
ns
of
year
s ag
o
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)
mil
lio
ns
of
year
s ag
o
http://www-rohan.sdsu.edu/~rhmiller/depositionfeatures1/
Geologic Time Scale
Precambrian Events
after (http://www.ucmp.berkeley.edu/precambrian/precambrian.html)
mil
lio
ns
of
year
s ag
o
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
ren
ts
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