Transcript Geologic Time

Geologic Time
Geologic time

Gigaannus:


Ga= Billion years
Billion years ago:

BYA
Major divisions of geologic time
Cenozoic
Mesozoic
Paleozoic
Precambrian
Early Earth History

Precambrian

Longest time unit
Biological events

Primordial puddle
Amino acids
formed
 Invertebrates
developed

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
Clicker
• Divisions between ERAS in
geologic time is based on?
a)Mass extinctions
b)Ice ages
c)Exfoliation
d)Volcanic eruptions
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D
4%
A
96%
Paleozoic, cont…
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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.
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

Mesozoic, contd…

Jurassic



Reptiles dominated
Big dinosaurs!
Birds appeared
Mesozoic, cont’d



Pangaea breaks up
(completely)
Volcanic activity
Dinosaurs become
extinct
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.
Clicker
When watching an old movie of Stone Age people
battling dinosaurs, you should know the story in the
movie is fiction because
A. stone age people were intelligent enough to
avoid dinosaurs.
B. stone age people and dinosaurs were not in
competition for the same food.
C. stone age people and dinosaurs lived at the same
time, but in different environments.
D. stone age people and dinosaurs did not exist at
the same time.
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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.
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
Michigan’s Geologic
History
• Precambrian
o
o
o
o
Metamorphic rock
MI was tectonically active
Copper and Iron
Fossilized algae (stromatolites)
• Paleozoic
o 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
• Mesozoic
o 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
• Cenozoic
o Glaciers
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B
4%
C
4%
A
92%
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.
EXAMPLES OF RADIOACTIVE
ISOTOPES

238Uranium

14Carbon
Parent product
(Unstable)
decays to
decays to
206Lead
16Nitrogen
daughter product
(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.
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.
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

14C
= 5,730 years
238U
= 4.5 billion years
40K
= 1.248 billion years
C-14
C-14
N-16
1 half life
It would take 5,730 years for half of the
14C
atoms in an object to decay to 16Nitrogen