Lecture Outlines
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Chapter 12
Earth Science 11e
Tarbuck/Lutgens
© 2006 Pearson Prentice Hall
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Earth Science, 11e
Earth’s History: A Brief
Summary
Chapter 12
Precambrian era
4.5 billion to 540 million years ago
88% of Earth's history
Only sketchy knowledge
Most Precambrian rocks are devoid of
fossils
Precambrian era
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
Continental structures today
Figure 12.3
Precambrian era
Earth's atmosphere
• Primitive atmosphere formed from volcanic
gases
• A process called outgassing
• Water vapor, carbon dioxide, nitrogen, and several
trace gases
• Very little free oxygen
• Water vapor condenses and forms primitive
oceans as Earth cools
Precambrian era
Earth's atmosphere
• Bacteria evolve
• Plants evolve and photosynthesis produces
oxygen
• Oxygen content in the atmosphere increases
• By about 4 billion years after Earth formed,
abundant ocean-dwelling organisms that require
oxygen existed
Precambrian era
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)
Precambrian era
Precambrian fossils
• Plant fossils date from the middle Precambrian
• Animal fossils date from the late Precambrian
• Diverse and multicelled organisms exist by the
close of the Precambrian
The geologic time scale
Figure 12.2
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
Paleozoic era
Early Paleozoic history
• North America
• 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
Reconstruction of Earth in
early Paleozoic time
Figure 12.7
Paleozoic era
Early Paleozoic life
• Restricted to seas
• Vertebrates had not yet evolved
• Life consisted of several invertebrate groups
• Trilobites
• Brachiopods
• Cephalopods
• First organisms with hard parts, such as shells –
perhaps for protection
Natural cast of a trilobite
Figure 12.5 A
Evolution of major groups
of organisms
Figure 12.6
Paleozoic era
Late Paleozoic history
• 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
Formation of Pangaea in
late Paleozoic time
Figure 12.10 C
Paleozoic era
Late Paleozoic life
• 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
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
Mesozoic era
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
Reconstruction of Earth in
the late Jurassic period
Figure 12.13 B
Mesozoic era
Mesozoic life
• 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
Major reptile groups in
the Mesozoic era
Figure 12.16
Mesozoic era
Mesozoic life
• 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
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
Cenozoic era
North America
• Many events of mountain building, volcanism,
and earthquakes in the West
• Eastern North America
• Stable with abundant marine sedimentation
• Eroded Appalachians were raised by isostatic
adjustments
Cenozoic era
North America
• Western North America
• 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)
Cenozoic era
North America
• Western North America
• Volcanic activity is common
• Fissure eruptions form the Columbia Plateau
• Volcanoes form from northern California to the
Canadian border
• Coast Ranges form
• Sierra Nevada become fault block mountains
Cenozoic era
Cenozoic life
• Mammals replace reptiles as the dominant land
animals
• Angiosperms (flowering plants with covered
seeds) dominate the plant world
• Strongly influenced the evolution of both birds and
mammals
• Food source for both birds and mammals
Cenozoic era
Cenozoic life
• Two groups of mammals evolve after the
reptilian extinctions at the close of the
Mesozoic
• Marsupials
• Placentals
Cenozoic era
Cenozoic life
• Mammals diversify quite rapidly and some
groups become very large
• e.g., Hornless rhinoceros, which stood nearly 16 feet
high
• Many large animals became extinct
• Humans evolve
End of Chapter 12