Transcript Precambrian Time - Gordon State College

Conceptual
Physical
Science
5th Edition
Chapter 23:
GEOLOGIC TIME—
READING THE ROCK
RECORD
© 2012 Pearson Education, Inc.
© 2012 Pearson Education, Inc.
This lecture will help you
understand:
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•
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The Rock Record-Relative Dating
Radiometric Dating
Geologic Time
Precambrian Time
The Paleozoic Era
The Mesozoic Era
The Cenozoic Era
Early History in a Capsule
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The Rock Record—
Relative Dating
• Earth is ~4.5 billion years old.
• Compared to a single calendar year:
—Formation of Earth
—Oldest rocks
—Bacterial life
—Dinosaurs
—Homo sapiens
—Human history
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Jan. 1
Feb. 26
Mar. 23
Dec. 14 to 26
Dec. 31 @11:50 pm
Dec. 31 @11:59 pm
The Rock Record—
Relative Dating
Uniformitarianism
Uniformitarianism is the assumption that Earth’s
geology is the result of slow processes over
long periods of time.
Assumes that natural laws have been constant
throughout geologic history.
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The Rock Record—
Relative Dating
The rock record is like a very long, old
book with many pages that are tattered,
torn, indecipherable, and missing.
Two methods of dating rock:
• Relative dating—relative age, the ordering of
rocks in sequence by comparative ages
• Radiometric dating—absolute age, actual age
of rock determined in a laboratory
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The Rock Record—
Relative Dating
Original horizontality:
• New layers of sediment are horizontally
laid down over older layers.
Superposition:
• In undeformed sequences of rock, top
layers are younger than bottom layers.
Cross-cutting:
• A fault or intrusion that cuts into a rock is
younger than the rock it cuts through.
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The Rock Record—
Relative Dating
Inclusion:
• Any inclusion is older than the rock
containing it.
Lateral continuity:
• Allows us to date separated rock
outcrops from similar characteristics.
Faunal succession:
• Fossil organisms follow one another in a
definite, irreversible time sequence.
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The Rock Record—
Relative Dating
Unconformities
Gaps in the rock
record are called
unconformities. An
angular
unconformity
happens when tilted
or folded rock is
covered by
younger, horizontal
rock.
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The Rock Record—Relative Dating
CHECK YOUR NEIGHBOR
Three dikes (igneous intrusion) cut into a rock body.
Which dike is the oldest, and which is the youngest?
A.
B.
C.
D.
A is oldest, then B, and C is the youngest.
C is oldest, then B, and A is the youngest.
B is oldest, then A, and C is the youngest.
A is oldest, then C, and B is the youngest.
© 2012 Pearson Education, Inc.
The Rock Record—Relative Dating
CHECK YOUR ANSWER
Three dikes (igneous intrusion) cut into a rock body.
Which dike is the oldest, and which is the youngest?
A.
B.
C.
D.
A is oldest, then B, and C is the youngest.
C is oldest, then B, and A is the youngest.
B is oldest, then A, and C is the youngest.
A is oldest, then C, and B is the youngest.
© 2012 Pearson Education, Inc.
The Rock Record—Relative Dating
CHECK YOUR NEIGHBOR
The embedded rocks (inclusions) in the sedimentary layers
are
A.
B.
C.
D.
metamorphic.
older than the sedimentary layers.
younger than the sedimentary layers.
the same age as the layers.
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The Rock Record—Relative Dating
CHECK YOUR ANSWER
The embedded rocks (inclusions) in the sedimentary layers
are
A.
B.
C.
D.
metamorphic.
older than the sedimentary layers.
younger than the sedimentary layers.
the same age as the layers.
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Radiometric Dating
Radiometric dating gives the actual age of a rock
by measuring the ratio of radioactive isotopes to
their daughter products.
Half-life—the time it takes for half of the parent
isotopes to decay to their daughter products.
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Radiometric Dating
CHECK YOUR NEIGHBOR
Radiometric dating can give the actual age of a rock. An
exception to the “actual age” can be found in
A.
B.
C.
D.
sedimentary and some metamorphic rocks.
igneous rocks.
metamorphic rocks.
sedimentary rocks.
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Radiometric Dating
CHECK YOUR ANSWER
Radiometric dating can give the actual age of a rock. An
exception to the “actual age” can be found in
A.
B.
C.
D.
sedimentary and some metamorphic rocks.
igneous rocks.
metamorphic rocks.
sedimentary rocks.
Explanation:
In a sedimentary rock, the age of individual minerals can be
determined but not the age of when the sedimentary rock formed. In
a mineral reheated by metamorphism, the “time clock” is reset,
complicating estimation of the rock’s age. The date obtained will be
the date of the metamorphic event, not the original age of the mineral.
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Geologic Time
The geologic time scale—a “calendar” of
Earth history.
• Originally created using
relative dates
• Specific dates using
radiometric dating
• Subdivides geologic history
into units:
Eons, eras, periods, and
epochs based on changes
in life forms
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Precambrian Time
The Precambrian ranges from 4.5 billion
years ago to ~543 million years ago.
• ~90% of Earth’s history
• Considerable volcanic activity
• Meteorite bombardment
• Cyanobacteria
• Soft-bodied organisms
• Primitive atmosphere and ocean
• Beginnings of lithospheric plate formation
and movement
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Precambrian Time
Precambrian fossils:
• Most common are stromatolites
—Material deposited by algae
—Microfossils of bacteria and algae
—Importance of cyanobacteria
• Plant fossils—middle Precambrian
• Primitive animal fossils—late Precambrian
• Diverse and multi-celled organisms existed by
the close of the Precambrian
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Precambrian Time:
Transformation of Earth’s Atmosphere
• First atmosphere:
– primarily hydrogen and helium
• Second atmosphere:
– Volcanic outgassing and cometary impacts
– Rich in CO2 and H2O, no free oxygen
– H2O condensed to form oceans
• Third atmosphere:
–
–
–
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Removal of CO2 to rocks
Nitrogen increase
Oxygen increase (photosynthesis)
Development of O3
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Precambrian Time: Transformation of Earth’s Atmosphere
CHECK YOUR NEIGHBOR
The development of free oxygen was crucial to the
emergence of life on Earth, because it led to the formation
of
A.
B.
C.
D.
air for animals to breathe.
ozone, O3, which helped screen Earth from harmful incoming UV
radiation.
ozone, O3, which primitive organisms could breathe.
the oceans, where life emerged.
© 2012 Pearson Education, Inc.
Precambrian Time: Transformation of Earth’s Atmosphere
CHECK YOUR ANSWER
The development of free oxygen was crucial to the
emergence of life on Earth, because it led to the formation
of
A.
B.
C.
D.
air for animals to breathe.
ozone, O3, which helped screen Earth from harmful incoming
UV radiation.
ozone, O3, which primitive organisms could breathe.
the oceans, where life emerged.
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Precambrian Time: Transformation of Earth’s Atmosphere
CHECK YOUR NEIGHBOR
The evolution of cyanobacteria helped oxygen escape to
the atmosphere by
A.
B.
C.
D.
keeping the carbon and expelling the oxygen.
photosynthesis.
releasing it from carbon dioxide.
All of the above.
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Precambrian Time: Transformation of Earth’s Atmosphere
CHECK YOUR ANSWER
The evolution of cyanobacteria helped oxygen escape to
the atmosphere by
A.
B.
C.
D.
keeping the carbon and expelling the oxygen.
photosynthesis.
releasing it from carbon dioxide.
All of the above.
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The Paleozoic Era
Spans ~300 million years. Six periods:
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Cambrian
Ordovician
Silurian
Devonian
Carboniferous
Permian
Periods are characterized by changes in life forms.
Fossil representation due to hardened body parts.
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The Paleozoic Era
Each period had changes:
• In life forms.
• In tectonics.
• In sea level—rise and fall of sea level.
—Shallow seas covered the continents.
—Marine life flourished.
—Changing sea levels contributed to
diversification of life forms.
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The Paleozoic Era
The Cambrian Period—543 to 490 Ma
The “Cambrian explosion”—great diversity
of life forms evolved during this time.
Hard-bodied organisms:
— Ability of organisms to secrete calcium
carbonate and calcium phosphate for
formation of an outer skeleton.
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The Paleozoic Era
The Ordovician Period—490 to 443 Ma
Abundant and diverse marine life:
• Emergence of vertebrates (e.g., jawless fishes)
• Surge in rate of extinctions
Many landmasses on journey to become
southern continent of Gondwanaland:
• Situated close to South Pole
• Widespread glaciation
• Sea level drops and shallow-water
invertebrates deprived of habitat
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The Paleozoic Era
The Silurian Period—443 to 417 Ma
Supercontinent of Gondwanaland near the
South Pole
Ancestral North America and Europe begin
convergence and are situated near equator
Terrestrial life—plants, scorpions, and
millipedes
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The Paleozoic Era
The Devonian Period—417 to 354 Ma
Gondwanaland completely formed in Southern
Hemisphere
North America and Eurasia joined as continent of
Laurasia in Northern Hemisphere
Devonian known as “age of fishes”
• Two groups of bony fishes:
— Lung fish
— Lobe-finned fish, which evolved to become the
amphibians
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The Paleozoic Era
The Carboniferous Period—354 to 290 Ma
Warm moist climate
Dense swamplands
• Present-day coal beds
Insects
Amniote egg
Collision of Gondwanaland with Laurasia
• Appalachian Mountains
• Ural Mountains
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The Paleozoic Era
The Permian Period—290 to 248 Ma
Amniote vertebrates continue to diversify
• Ancestral link to reptiles and mammals
Permian extinction
• ~95% of all marine species
• ~70% of all land species
Possible causes of extinction
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Redistribution of water and land
Changes in landmass elevations
Climate change
Lowering of sea levels
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The Paleozoic Era
CHECK YOUR NEIGHBOR
The Paleozoic experienced several fluctuations in sea
level. When sea level rises,
A.
B.
C.
D.
shallow seas cover the continents.
more water is tied up in glaciers making the climate colder.
the climate turns warmer, and swamps form.
ocean basins become shallow.
© 2012 Pearson Education, Inc.
The Paleozoic Era
CHECK YOUR ANSWER
The Paleozoic experienced several fluctuations in sea
level. When sea level rises,
A.
B.
C.
D.
shallow seas cover the continents.
more water is tied up in glaciers making the climate colder.
the climate turns warmer, and swamps form.
ocean basins become shallow.
© 2012 Pearson Education, Inc.
The Paleozoic Era
CHECK YOUR NEIGHBOR
At the end of the Permian Period, sea level lowered. The
lowering of sea level could be a result of
A.
B.
C.
D.
glaciation as Pangaea drifted near the South Pole.
the collision of Gondwanaland and Laurussia to form Pangaea.
tectonics and climate change.
all of the above.
© 2012 Pearson Education, Inc.
The Paleozoic Era
CHECK YOUR ANSWER
At the end of the Permian period, sea level lowered. The
lowering of sea level could be a result of
A.
B.
C.
D.
glaciation as Pangaea drifted near the South Pole.
the collision of Gondwanaland and Laurussia to form Pangaea.
tectonics and climate change.
all of the above.
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The Mesozoic Era
Mesozoic era spans ~180 million years
from 248 Ma to 65 Ma
Three Periods
• Triassic
• Jurassic
• Cretaceous
Often called the “age of reptiles”
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The Mesozoic Era
Mesozoic history:
• Begins with much of the world’s land above
sea level
• Seas invade western North America
• Breakup of Pangaea begins forming the
Atlantic Ocean
• Subduction of oceanic crust produced
widespread deformation, volcanism, and
mountain building along the Western coast
• Mountains of western North America began
forming
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The Mesozoic Era
Mesozoic life
Survivors of the great Paleozoic
extinction:
• True pines and redwoods
• Flowering plants
• Insects
• Reptiles (first true terrestrial animals) readily
adapt to the dry Mesozoic climate
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The Mesozoic Era
Mesozoic life:
• Dinosaurs dominated.
• One group of reptiles led to the birds.
• Many reptile groups, along with many other
animal groups, become extinct at the close
of the Mesozoic.
• Possible Hypotheses for Extinction:
— Impact from large asteroid or comet.
— Extensive volcanism.
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The Mesozoic Era
CHECK YOUR NEIGHBOR
The breakup of Pangaea was the greatest tectonic
event in the Mesozoic. Of all the continental unions
that existed in Paleozoic time, which one survived
to this day?
A.
B.
C.
D.
Africa and Asia
The United States and Mexico
Asia and India
Europe and Asia
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The Mesozoic Era
CHECK YOUR ANSWER
The breakup of Pangaea was the greatest tectonic
event in the Mesozoic. Of all the continental unions
that existed in Paleozoic time, which one survived
to this day?
A.
B.
C.
D.
Africa and Asia
The United States and Mexico
Asia and India
Europe and Asia
Comment:
Asia and India came together in the Cenozoic,
producing the Himalayas.
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The Cenozoic Era
Cenozoic—a smaller fraction of geologic
time than the Paleozoic or Mesozoic
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65 million years ago to the present
Often called the “age of mammals”
Pangaea’s breakup complete
Two Periods:
• Tertiary
• Quaternary
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The Cenozoic Era
North America and Greenland split from
Europe.
Alps and Himalayas formed by collisions of
land masses.
Ridge formation and plate movement led
to San Andreas Fault.
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The Cenozoic Era
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•
Climates cooled
Glaciation in temperate zones
One-third of the land covered by ice
Marine mammals and large land animals
evolved
• Humans evolved
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The Cenozoic Era
CHECK YOUR NEIGHBOR
Glaciation during the Cenozoic resulted in
A.
B.
C.
D.
lowering of sea level worldwide.
carving of the Swiss Alps.
land bridge connections between various continents.
all of the above.
© 2012 Pearson Education, Inc.
The Cenozoic Era
CHECK YOUR ANSWER
Glaciation during the Cenozoic resulted in
A.
B.
C.
D.
lowering of sea level worldwide.
Carving of the Swiss Alps.
land bridge connections between various continents.
all of the above.
© 2012 Pearson Education, Inc.
The Cenozoic Era
CHECK YOUR NEIGHBOR
Which of the following is the Cenozoic era NOT noted for?
A.
B.
C.
D.
E.
the debut of humans.
ice ages.
swampy conditions that later developed fossil fuels
great mountain building activity.
the San Andreas Fault.
© 2012 Pearson Education, Inc.
The Cenozoic Era
CHECK YOUR ANSWER
Which of the following is the Cenozoic era NOT noted for?
A.
B.
C.
D.
E.
the debut of humans.
ice ages.
swampy conditions that later developed fossil fuels.
great mountain building activity.
the San Andreas Fault.
© 2012 Pearson Education, Inc.