Transcript Chapter_19_Lecture

Essentials of Geology, 9e
Earth History: A
Brief Summary
Chapter 19
Early evolution of Earth
Origin of planet Earth
• Most researchers believe that Earth and
the other planets formed at essentially the
same time from the same primordial
material as the Sun
• Nebular hypothesis
 Solar system evolved from an enormous
rotating cloud called the solar nebula
 Nebula was composed mostly of hydrogen
and helium
Early evolution of Earth
Origin of planet Earth
• Nebular hypothesis
 About 5 billion years ago the nebula began to
contract
 Assumes a flat, disk shape with the protosun
(pre-Sun) at the center
 Inner planets begin to form from metallic
and rocky clumps of substances with high
melting points
 Larger outer planets began forming from
fragments with a high percentage of ices water, carbon dioxide, methane and
ammonia
Early evolution of Earth
Formation of Earth’s layered structure
• As Earth formed, high-velocity impacts
caused the temperature to increase and
iron and nickel began to melt and sink
toward the center
• Buoyant masses of molten rock rose to
the surface to produce a primitive crust
Early evolution of Earth
Formation of Earth’s layered structure
• Early chemical segregation established
the three basis divisions of Earth’s
interior
 an iron-rich core
 a thin, primitive crust
 the mantle between the core and crust
• A primitive atmosphere evolved as
gaseous materials escaped from Earth’s
interior
Earth’s atmosphere evolves
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
Earth’s atmosphere evolves
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
Earth’s history
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
Earth’s history
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
Precambrian shields
Figure 19.3
Earth’s history
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)
Earth’s history
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 19.2
Earth’s history
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
Earth’s history
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 19.9 B
Earth’s history
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
A natural cast of a trilobite
Figure 19.7 A
Earth’s history
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 19.9 D
Earth’s history
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
Earth’s history
Paleozoic era
• Late Paleozoic life
 Insects invade the land
 Amphibians diversify rapidly
 Extensive coal swamps develop
Earth’s history
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
Earth’s history
Mesozoic era
• Mesozoic history
 Breakup of Pangaea begins forming the
Atlantic ocean
 North American plate began to override the
Pacific plate
 Mountains of western North America began
forming
Reconstruction of Earth in
the late Jurassic period
Figure 19.13 B
Earth’s history
Mesozoic era
• Mesozoic life
 Survivors of the great Paleozoic extinction
 Gymnosperms become the dominant trees
 Reptiles (first true terrestrial animals) readily
adapt to the dry Mesozoic climate
 Reptiles have shell-covered eggs that can be
laid on the land
Major reptile groups in
the Mesozoic era
Figure 19.14
Earth’s history
Mesozoic era
• Mesozoic life
 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
 One hypothesis is that a large asteroid or
comet struck Earth
 Another possibility is extensive volcanism
The Chicxulub impact site
Figure 19 B
Earth’s history
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
Earth’s history
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
Earth’s history
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 is formed, Rockies are reelevated, rivers erode the Grand and
Black canyons, and volcanic activity is
abundant
Earth’s history
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
Earth’s history
Cenozoic era
• Cenozoic life
 Two groups of mammals evolve after the
reptilian extinctions at the close of the
Mesozoic
 Marsupials
 Placentals
Earth’s history
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 19