ESC 1000

1
ESC 1000

• Lecture 7
• Earths History
• Ch 12

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Precambrian Era

• 4.5 billion to 540 million years ago
• 85 of Earth's history
• Only sketchy knowledge
• Most Precambrian rocks are devoid of fossils

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Precambrian Time

• Subdivided into
• Hadean (beneath the Earth) about the 1st billion
  yrs
• Archaen (ancient) 1-1.5 byrs
• Proterozoic (early life)

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Hadean

• Formation of Earths crust
• Primitive atmosphere formed from volcanic gases
• A process called outgassing
• Water vapor, carbon dioxide, nitrogen, and
  several trace gases
• Very little free oxygen

5
Archaen

• Marked by 1st appearance of life
• Cyanobacteria
• Capable of photosynthesis
• Oxygen increases to about 10
• Precambrian fossils
• Most common are stromatolites
• Material deposited by algae
• Common about 2 billion years ago
• Microfossils of bacteria and algae have been
  found in chert
• Southern Africa (3.1 billion years of age)
• Lake Superior area (1.7 billion years of age)
• Atmospheric water vapor begins to condense to
  form oceans

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• Precambrian rocks
• Most are buried from view
• Each continent has a "core area" of Precambrian
  rocks called a shield
• Extensive iron ore deposits
• Absent are fossil fuels

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Proterozoic

• Organisms grow in abundance
• 1st soft-bodied marine, multi-celled organisms
  emerge
• Oxygen increases
• Continuation of crust formation
• Small continents emerging

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Paleozoic Era

• 540 million years ago to about 248 million years
  ago
• First life forms with hard parts
• Abundant Paleozoic fossils
• Early Paleozoic history
• Southern continent of Gondwanaland exists

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• A barren lowland
• Seas move inland and recede several times and
  shallow marine basins evaporate leaving rock salt
  and gypsum deposits
• Taconic orogeny, a mountain building event,
  affects eastern North America

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• Supercontinent of Pangaea forms
• Several mountain belts formed during the
  movements of the continents
• World's climate becomes very seasonal, causing
  the dramatic extinction of many species

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• Organisms diversified dramatically
• Land plants
• Fishes evolve into two groups of bony fish
• Lung fish
• Lobe-finned fish which become the amphibians
• Insects invade the land
• Amphibians diversify rapidly
• Extensive coal swamps develop

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• Subdivided into 6 periods
• Cambrian (570-505 mya)
• Ordivician (505-438 mya)
• Silurian (408-360 mya)
• Devonian (408-360 mya)
• Carboniferous (360-286 mya)
• Permian (286-245 mya)

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Cambrian

• Marked by organisms with hard parts or
  ecto-skeletons (invertebrates)
• Trilobites mud burrowing scavengers
• Brachiopods lampshells
• Cephalopods i.e. squids, octopus, etc

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brachiopods
trilobites
cephalopods
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Ordivician

• Increase in number types of organisms
• First clams, gastropods corals appear
• Appearance of 1st fish vertebrates
• Flooding often covered the continents with
  shallow seas

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Silurian

• Emergence of 1st land plants developed from green
  algae
• Appearance of spiders, millipedes, scorpions
• Shallow seas in northern U.S. evaporated ?
  deposits of rock salt gypsum beds

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Devonian

• Age of Fishes
• Rise of 1st amphibians
• Oxygen level increases

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Carboniferous

• Water swamps plentiful
• Creation of coal beds from decaying remains of
  plant life
• Insect life flourished
• 1st reptiles appear

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Permian

• Age of dry desert climate evaporating seas
• Age of Reptiles
• Permian extinction

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Mesozoic Era

• 248 million years ago to about 65 million years
  ago
• Often called the age of dinosaurs
• 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

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• Mesozoic history
• North American plate began to override the
  Pacific plate
• Mountains of western North America began forming
• Mesozoic life
• Survivors of the great Paleozoic extinction
• Gymnosperms become the dominant trees

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• Reptiles (first true terrestrial animals) readily
  adapt to the dry Mesozoic climate
• Reptiles have shell-covered eggs that can be laid
  on the land
• Dinosaurs dominate
• 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

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• Many reptile groups, along with many other animal
  groups, become extinct at the close of the
  Mesozoic
• One hypothesis is that a large asteroid or comet
  struck Earth
• Another possibility is extensive volcanism

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• Subdivided into 3 periods
• Triassic (245-208 mya)
• Jurassic (208-144 mya)
• Cretaceous (144-65 mya)

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Triassic

• Development of new species of animal and fish,
  reptiles,dinosaurs
• Earth above sea level
• Appearance of small mammals

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Jurassic

• Dinosaurs
• Archeopteryx
• Flowering plants

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Cretaceous

• Extinction of the Dinosaur
• How? Why?
• Theories
• Meteorites hitting the Earth blocking sunlight
  and causing dramatic climatic changes thus
  destroying global food supply chain

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Cenozoic era

• 65 million years ago to the present
• Often called the age of mammals
• Smaller fraction of geologic time than either the
  Paleozoic or the Mesozoic
• North America
• Most of the continent was above sea level
  throughout the Cenozoic era

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• North America
• Many events of mountain building, volcanism, and
  earthquakes in the West
• Eastern North America
• Stable with abundant marine sedimentation
• Building of the Rocky Mountains was coming to an
  end
• Large region is uplifted
• Basin and Range Province formed
• Re-elevates the Rockies
• Rivers erode and form gorges (e.g., Grand Canyon
  and Black Canyon)

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• Subdivided into 2 periods
• Tertiary (65-1.6 mya)
• Quaternary (1.6 mya-present)

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Tertiary

• Age of Mammals
• Physical landscapes and life forms of our modern
  world developed
• Many volcanic mountain building events in
  Western US (Cascades)
• Eastern US dominated by erosion sedimentation

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Quaternary

• Glacial advances retreats
• Appearance of 1st human fossils
• Homo erectus
• Homo sapiens
• Cro Magnon