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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