Earth History: A Brief Summary
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

Origin of planet Earth
Nebular hypothesis
 About
5 billion years ago the nebula began to contract
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
 Assumes
Nebular Hypothesis
 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
 Formation
of Earth’s layered structure
Early
chemical segregation established the three basis divisions
of Earth’s in-terior
 an
iron-rich core
 a thin, primitive crust
 the mantle between the core and crust
A
primitive atmosphere evolved as gas-eous materials escaped
from Earth’s interior
Earth’s atmosphere evolves
 Primitive
A
atmosphere formed from volcanic gases
process called outgassing
Water vapor, carbon dioxide, nitrogen, and several trace gases
Very
 Water
little free oxygen
vapor condenses and forms primitive oceans as Earth
cools
 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
 Precambrian
era
Precambrian
rocks
 Most
are buried from view
continent has a "core area" of Precambrian rocks called a shield
 Extensive iron ore deposits
 Absent are fossil fuels
 Each
Precambrian shields
 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
 Plant
fossils
fossils date from the middle Precambrian
fossils date from the late Precambrian
 Diverse and multicelled organisms exist by the close of the Precambrian
 Animal
The geologic time scale
 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
 Paleozoic
Early
continent of Gondwanaland exists
era
Paleozoic history
 North
America
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
A
Reconstruction of early Paleozoic time
 Paleozoic
Early
era
Paleozoic life
 Restricted
to seas
had not yet evolved
 Life consisted of several invertebrate groups
 Trilobites
 Brachiopods
 Cephalopods
 First organisms with hard parts, such as shells – began the Cambrian
Explosion
 Vertebrates
 Paleozoic
Late
era
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
 Paleozoic
Late
era
Paleozoic life
 Organisms
diversified dramatically
plants
 Fishes evolve into two groups of bony fish
 Lung fish
 Lobe-finned fish which become the amphibians
 Land
 Paleozoic
Late
era
Paleozoic life
 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
 Mesozoic
era
Mesozoic
history
 Breakup
of Pangaea begins forming the Atlantic ocean
American plate began to override the Pacific plate
 Mountains of western North America began forming
 North
 Mesozoic
era
Mesozoic
life
 Survivors
of the great Paleozoic extinction
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
 Gymnosperms
 Mesozoic
era
Mesozoic
life
 Dinosaurs
dominate
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
 One
Mass Extinctions
 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, vol-canism, and earthquakes in the
West
 Eastern
North America
 Stable with abundant marine sedimen-tation
 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 is formed,
Rockies are re-elevated, rivers erode the Grand and Black canyons,
and volcanic activity is abundant
 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
Humans Impact on Earth
Key Terms Chapter 14
Photosynthesis
Cell
DNA
Prokaryotes, eukaryotes
Domain
Evolution, natural selection
Species
Fossil
Trace fossil
Kingdom
Gymnosperm, angiosperm
Mass extinction
Key Terms Chapter 15
Natural resource
Renewable and non-renewable resources
Fossil fuel
Peat, lignite, bituminous, anthracite coals
Petroleum, oil and natural gas, tar sand and oil shale
Biomass energy
Nuclear energy
Hydroelectric energy
Solar, tidal, wind energy
Ore