18.2 Precambrian Time: Vast and Puzzling

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18.2 Precambrian Time Vast and Puzzling
? The Precambrian encompasses immense geological
time, from Earths distant beginnings 4.56
billion years ago until the start of the Cambrian
period, over 4 billion years later.
? Precambrian Rocks
Shields are large, relatively flat expanses of
ancient metamorphic rock within the stable
continental interior.
Much of what we know about Precambrian rocks
comes from ores mined from shields.
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Geologic Time Scale
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Remnants of Precambrian Rocks
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18.2 Precambrian Time Vast and Puzzling
? Earths Atmosphere Evolves
Earths original atmosphere was made up of
gases similar to those released in volcanic
eruptions todaywater vapor, carbon dioxide,
nitrogen, and several trace gases, but no oxygen.
Later, primary plants evolved that used
photosynthesis and released oxygen.
Oxygen began to accumulate in the atmosphere
about 2.5 billion years ago.
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18.2 Precambrian Time Vast and Puzzling
? Precambrian Fossils
The most common Precambrian fossils are
stromatolites.
Stromatolites are distinctively layered mounds
or columns of calcium carbonate. They are not the
remains of actual organisms but are the material
deposited by algae.
Many of these ancient fossils are preserved in
cherta hard dense chemical sedimentary rock.
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Stromatolites

• Stromatolites of Hamelin Pool

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18.2 Paleozoic Era Life Explodes
? Following the long Precambrian, the most recent
540 million years of Earths history are divided
into three eras Paleozoic, Mesozoic, and
Cenozoic.
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18.2 Paleozoic Era Life Explodes
? Early Paleozoic History
During the Cambrian, Ordovician, and Silurian
periods, the vast southern continent of Gondwana
encompassed five continents (South America,
Africa, Australia, Antarctica, and part of Asia).
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Gondwana and the Continental Landmasses
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18.2 Paleozoic Era Life Explodes
? Early Paleozoic Life
Life in early Paleozoic time was restricted to
the seas.
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Life in the Ordovician Period
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18.2 Paleozoic Era Life Explodes
? Late Paleozoic History
Laurasia is the continental mass that formed
the northern portion of Pangaea, consisting of
present-day North America and Eurasia.
By the end of the Paleozoic, all the
continents had fused into the supercontinent of
Pangaea.
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Late Paleozoic Plate Movements
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18.2 Paleozoic Era Life Explodes
? Late Paleozoic Life
Some 400 million years ago, plants that had
adapted to survive at the waters edge began to
move inland, becoming land plants.
The amphibians rapidly diversified because
they had minimal competition from other land
dwellers.
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Armor-Plated Fish
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Model of a Pennsylvanian Coal Swamp
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18.2 Paleozoic Era Life Explodes
? The worlds climate became very seasonal,
probably causing the dramatic extinction of many
species.
? The late Paleozoic extinction was the greatest
of at least five mass extinctions to occur over
the past 500 million years.
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18.2 Mesozoic Era Age of Reptiles
? Dinosaurs were land-dwelling reptiles that
thrived during the Mesozoic era. (Jurassic Period)
? Mesozoic History
A major event of the Mesozoic era was the
breakup of Pangaea.
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18.2 Mesozoic Era Age of Reptiles
? Mesozoic Life
Gymnosperms are seed-bearing plants that do
not depend on free-standing water for
fertilization.
The gymnosperms quickly became the dominant
plants of the Mesozoic era.
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Canadian Rockies Were Formed Throughout the
Cretaceous Period
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18.2 Mesozoic Era Age of Reptiles
? The Shelled Egg
Unlike amphibians, reptiles have shell-covered
eggs that can be laid on the land.
The elimination of a water-dwelling stage
(like the tadpole stage in frogs) was an
important evolutionary step.
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18.2 Mesozoic Era Age of Reptiles
? Reptiles Dominate
With the perfection of the shelled egg,
reptiles quickly became the dominant land animals.
At the end of the Mesozoic era, many reptile
groups became extinct. (end of the Cretaceous)
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The Flying Reptile Pteranodon
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Fossil Skull of an Extinct Crocodile
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18.2 Cenozoic Era Age of Mammals
? The Cenozoic era is divided into two periods of
very unequal duration, the Tertiary period and
the Quaternary period.
? Plate interactions during the Cenozoic era
caused many events of mountain building,
volcanism, and earthquakes in the West.
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18.2 Cenozoic Era Age of Mammals
? Mammalsanimals that bear live young and
maintain a steady body temperature replaced
reptiles as the dominant land animals in the
Cenozoic era.
? Angiospermsflowering plants with covered
seedsreplaced gymnosperms as the dominant land
plants.
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18.2 Cenozoic Era Age of Mammals
? Mammals Replace Reptiles
Adaptations like being warm blooded,
developing insulating body hair, and having more
efficient heart and lungs allow mammals to lead
more active lives than reptiles.
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Fossils from La Brea Tar Pits
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18.2 Cenozoic Era Age of Mammals
? Large Mammals and Extinction
In North America, the mastodon and mammoth,
both huge relatives of the elephant, became
extinct. In addition, saber-toothed cats, giant
beavers, large ground sloths, horses, camels,
giant bison, and others died out on the North
American continent.
The reason for this recent wave of extinctions
puzzles scientists.
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The Geologic Time Scale

• Paleozoic Era (six periods) Means Ancient
  Life
• Cambrian Period (marine invertebrates)
  (540 million years ago)
• Trilobites
• Brachiopods
• Ordovician Period (primitive fish)
  vertebrates (490 million yrs. ago)
• Ostracoderms (bony
  plated fish)
• No plant life on land
• Silurian Period (marine vertebrates and
  invertebrates) (443 mya)
• Eurypterids
• Earliest land plants
  and animals such as spiders and
• Millipedes

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The Geologic Time Scale

• Devonian Period (Age of Fishes)(417 mya)
• Lung fish
• Ichthyostega (first
  true amphibian)
• Land plants such as
  giant horsetails, ferns and cone bearing plants
• Carboniferous Period(Mississippian 354
  mya,Pennsylvanian 323 mya)
• Forests and swamps
  cover much of the land
• Coal formation
  begins
• Amphibians and fish
  thrive
• Crinoids (relative
  of modern sea star) thrive
• Reptiles appear at
  the end of this period
• Permian Period (290 mya)
• Mass extinction of
  numerous life forms
• Appalachian
  Mountains form
• Trilobites become
  extinct
• Pangaea comes
  together

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The Geologic Time Scale

• The Mesozoic Era (three periods)
• Triassic Period (248 mya)
• Dinosaurs
  (Terrible Lizards)
  
• Ranged in size
  from small squirrel to 30 meters long
• Ichthyosaurs
• Ammonite
  (shellfish similar to the nautilus)
• 1st mammals appear
• Jurassic Period (206 mya)
  
• Apatosaurus,
  Stegosaurus, pterosaurs(flying reptiles)
• First birds appear
• Cretaceous Period (144 mya)
• Tyrannasaurus Rex
• Angiosperms
  (flowering plants)
• Mass extinction of
  the dinosaurs

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The Geologic Time Scale

• The Cenozoic Era (The Age of Mammals)
• Teritiary Period
• Paleocene and Eocene Epochs (65
  mya 54.8 mya)
• Lemuroids
• Hyracotherium
  (ancestor of the horse)
• Flying squirrels,
  bats, whales
• Oligocene and Miocene Epochs
  (golden age of Mammals)
• Largest known land
  animals existed at this time
• Raccoons, wolves,
  foxes, saber toothed cat
• Modern polar ice
  caps began to form
• Pliocene Epoch
• Bear, dog, cat
  became fully evolved
• Continental ice
  sheets began to spread
• Bering Land
  bridge appeared as sea levels fell

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The Geologic Time Scale

• Quaternary Period
• Pleistocene Epoch
• Glaciation over
  Eurasia and North America
• Large mammal
  extinctions as humans entered the
• Holocene Epoch
• Ice age ends,
  sea levels rise 140 meters
• Great Lakes
  form
• Humans
  developed agriculture

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Questions

• Why are fossils rare in Precambrian rocks?
• Because possible fossils have been
  destroyed by weathering, erosion, volcanic
  activity and metamorphism and because early life
  forms lacked the hard parts that normally
  fossilize well
• How did the formation of Pangaea affect Paleozoic
  life-forms?
• The shallow inland seas disappeared,
  causing many species of marine invertebrates to
  die out
• How did the ice ages affect animal life during
  the Cenozoic Era?
• Warm-blooded, fur-covered mammals survived
  and became the predominant life-form
• Compare the Permian extinction with the
  Cretaceous extinction.
• Both extinctions allowed a new group of
  animals to become the dominant life-form in the
  following era Permian
  extinctionreptiles became dominant
• 
  Cretaceous extinctionmammals became dominant