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5/28/2015
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Geologic Time
What is Age?
• There are 2 kinds:
– Absolute Age – The number of years since the rock formed. (150 million years old, 10 thousand years old.)
– Relative Age – The age compared to the ages of other rocks. (older than this rock, younger than that rock.)
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Law of superposition
Which layer is oldest?
» Diagram this!
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Law of cross-cutting
Which layer is older 4 or 3?
» Diagram this!
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Law of Horizontality
Draw this!
A BREAK in the Earth’s crust.
A fault is always YOUNGER than the rock it cuts through.
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What is an Unconformity?
• The surface where new rock layers meet a much older rock surface beneath them.
• An unconformity shows where some rock layers have been lost because of erosion.
Unconformity
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Put in order!
Geologic time
Gigaannus:
Ga= Billion years
Billion years ago:
BYA
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Major divisions of geologic time
PrecambrianP
aleozoic
Mesozoic
Cenozoic
Early Earth History
Precambrian Longest time unit
Biological events Primordial puddle
Amino acids formed
Invertebrates developed
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Precambrian, contd…Geologic events
Very volcanic, many igneous rocks formed
Little is known about this era, because rocks were eroded, heated and pressurized, invertebrates are soft.
Paleozoic Era 544-286 MYA
Biological events
Mostly marine life forms:
Trilobites
Brachiopods and Crinoids still exist today
Fish
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Clicker• Divisions between ERAS in
geologic time is based on?
a)Mass extinctions
b)Ice ages
c)Exfoliation
d)Volcanic eruptions
TimerTimes up!
SMART Response QuestionTo set the properties right click and select
SMART Response Question Object->Properties...
Paleozoic, cont…
Appalachian Mountains started forming
First vertebrates
Plant life moved from ocean to land
Then animals moved to land.
Pangaea came together and major glaciers formed, caused mass extinctions of animals.
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Mesozoic Era 245-66.5 MYA
Divided into three periods:
Triassic
Jurassic
Cretaceous
Mesozoic, contd…
Triassic period Pangaea
separated
Climate dried out
Small dinosaurs appeared
First mammals
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Mesozoic, contd…
Jurassic
Reptiles dominated
Big dinosaurs!
Birds appeared
Mesozoic, cont’d
Pangaea breaks up (completely)
Volcanic activity
Dinosaurs become extinct
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Cenozoic, 66.4 MYA to present
Ice ages occurred
Himalayan mountains formed
Further evolution of plants and animals. Insects, small animals, Modern Humans appeared 200,000 years ago
Fossil
• Evidence such as the remains, imprints or traces of once living organisms preserved in rocks.
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Fossil types • Replacement fossil- form when bones, teeth or
shells are replaced by minerals dissolved in water.
• Carbonization fossil- forms when an animal is compressed, leaving behind a carbon film on the surrounding rock.
Fossil types Cast/Mold
• Cast- the part that is the shape of the original object.
• Mold- the cavity in the rock.
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Fossil types
• Original remains- insects can be completely preserved in crystallized tree sap (amber).
• Trace fossils- fossilized tracks and other evidence of animal activity.o Footprints
o Burrow holes
o Coprolites
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Michigan’s Geologic History
• Precambriano Metamorphic rock
o MI was tectonically active
o Copper and Iron
o Fossilized algae (stromatolites)
• Paleozoico MI was tropical
• Ocean (salt water)
• Coral => Petoskey stones
• MI basin bowl shaped
o Youngest rocks in the center older as you move away
Michigan’s Geologic History
• Mesozoico Jurassic rock the youngest what happened to the rest?
• Stolen!
• Unconformity
• What fossils would you not expect to find?
o Sorry no dinosaurs in your backyard
• Cenozoico Glaciers
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ABSOLUTE DATING
Absolute dating- Any method used to determine the age, in years, of a rock or other object. Radiometric Dating
Carbon dating
Uranium dating
Other methods dendrochronology
RADIOMETRIC DATING
Some isotopes of some elements break down (decay) into other elements over time. These are called radioactive isotopes.
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EXAMPLES OF RADIOACTIVE ISOTOPES
238Uranium decays to 206Lead
14Carbon decays to 16Nitrogen
Parent product daughter product
(Unstable) (stable)
RADIOMETRIC DATING
We know how long it takes uranium to decay to lead. This rate of decay is known as its half-life. This rate is quantifiable.
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HALF-LIFE
The half-life is the time it takes for half of the atoms of the parent product to decay to the daughter product.
14C = 5,730 years
238U = 4.5 billion years
40K = 1.248 billion years
C-14 C-14 N-161 half life
It would take 5,730 years for half of the 14C atoms in an object to decay to 16Nitrogen