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GEOLOGIC TIME
** Geologic time is divided into large blocks
based on the types of organisms that
dominated the Earth at that time**
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Precambrian Time
• 
4,600,000,000yrsagoto
543,000,000yrsago
• 
85%ofEarth’sHistory!!
• 
SimpleLifestartsinthe
oceans
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4.6 Billion Years Ago
A molten Earth forms
4.3 Billion Years Ago
Surface cools, forming the crust
n  Oldest
rock found in Australia & Canada
n  primitive
atmosphere forms from volcanic
eruptions (No Free oxygen gas).
n  Oceans
form (from water vapor released in
eruptions & comets)
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Early Earth
n Atmosphere
was made
of gases such as water
vapor, carbon dioxide,
and nitrogen
n Place
of turmoil –
volcanic eruptions,
meteors, storms,
radiation
n Unpleasant
environment for life
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Comparison of Atmospheres
What’s Different?
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Where did Life Start?
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o 
Where Did Life
Start?
Hydrothermal Ocean Vents
o 
Nutrient rich, possibly with complex molecules which may
have joined together to form structures such as cells
¢  Ocean
l 
covered in Ice
Extra protection from UV
radiation and opportunity
for organization
¢  Meteorites
l 
or Comets
Rich with building blocks of
life
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Early Life Hypothesis
n Life
developed from
simple chemicals in the
ocean and atmosphere
n HOW?
n Radiation
caused
chemicals to react and
form complex molecules
that made life possible
n These molecules joined to
form cells
Miller/Urey Experiment (1953)
n  Tried
to create
life from a
simulated
primitive
atmosphere.
n  Instead
created
complex
molecules, but
no cells.
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3.5 Billion Years Ago
n Oldest
fossils of bacteria
n The
early atmosphere did
not contain oxygen
n  The
first organisms were
prokaryotes
n Prokaryotes
= single-celled,
do not contain a nucleus
do not require oxygen
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** Video Connection –
n Describe
the early atmosphere and how life
could eventually be supported.
n How
did stromatolites influence life on
Earth or change the atmosphere?
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3.0 BYA: Photosynthesis and
Oxygen
n Stromatolites are huge colonies of
cyanobacteria
n What
is cyanobacteria?
n Prokaryotic organism that uses sunlight
to produce food (photosynthesize)
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Photosynthesis and Oxygen
n Photosynthesis
releases oxygen
into the oceans and air
n The
ozone layer begins to form and
reduce the amount of radiation
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3.5 BYA: Multicellular
Organisms
n After
1 billion years (3.5
BYA), larger organisms
(eukaryotes) appear in the
fossil record
n Eukaryotes
contain a
nucleus and other complex
structures
n More
complex, larger
single celled organisms
n Evolved
from prokaryotes
+ Precambrian Time – Check for
Understanding
Place the facts in each box in the correct order.
Earth’s Crust cools
Sun forms
Eukaryotes (cells with a
nucleus)
Oldest known rock
Left over material from our
sun collides to form the
planets
Cyanobacteria
(photosynthetic)
Earth was entirely molten
Bacteria or prokaryotes (cells
without a nucleus)
Atmosphere & oceans form
Multicellular life (examples:
sponges)
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Stop and Summarize
On page 72 in ISN…
Draw a line across middle of page
Label top half – Precambrian Time
Summarize in three sentences or less the
Precambrian time period. Then draw an
illustration of the period.
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Precambrian Time (Answers)
1. 
Sun forms
1. 
Oldest known rock
2. 
Left over material from our
sun collides to form the
planets
2. 
Bacteria or prokaryotes
(cells without a nucleus)
3. 
Cyanobacteria
(photosynthetic)
4. 
Eukaryotes (cells with a
nucleus)
5. 
Multicellular life (examples:
sponges)
3. 
Earth was entirely molten
4. 
Earth’s Crust cools
5. 
Atmosphere & oceans form