Earth Science, 10e.ppt

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Earth Science, 10e.ppt

Earth Science, 10e Edward J. Tarbuck Frederick K. Lutgens Earth’s History: A Brief Summary Chapter 11 Earth Science, 10e Stan Hatfield and Ken Pinzke Southwestern Illinois College Precambrian era 4.5 billion to 540 million years ago 88% of Earths 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 Precambrian shields Precambrian era Earths 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 Earths 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 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 eve

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