View of the earth's past


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PreCambrian and Paleozoic Eras

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View of the earth's past

  1. 1. A View of the Earth’sPastThe Geologic Time Scale
  2. 2.  Rock Record holds a fascinating story of the evolution of life on earth
  3. 3. The Geologic Time Scale Some organisms flourish then become extinct with the changes that occur on earth such as mountains forming and eroding, oceans rising and receding Scientists use the geologic time scale – gives the sequence and length of time these changes occurred
  4. 4. The Geologic Time Scale: The Geologic ColumnReview Law of Superposition Index fossils Relative ages of rocksGeologic Column – the ordered arrangement of rocklayers based on the ages of rocks
  5. 5. Law of Superposition
  6. 6. The Geologic Time Scale: The Geologic Column Rock layers distinguished from each other mainly by the types of fossils and the kinds of rocks found in the rock layers Upper layers of rock layers contain modern types of plants and animals Lower layers have older plants and animal fossils  Many contain EXTINCT animals and plants
  7. 7. The Geologic Time Scale: The Geologic Column Original theory of geologic column thought the rates of deposition were constant  Later it was discovered that the rates of deposition change over time  Radioactive dating development also helped refine the geologic column theory
  8. 8. The Geologic Time Scale: The Geologic Column According to the law of superposition, the position of a given rock layer is a clue to its relative age
  9. 9. Relative Age of Rocks
  10. 10. The Geologic Time Scale:Divisions of Geologic Time Geologic history is divided into sections, like a calendar, that represent major changes in the earth surface or climate changes  Geologists use these events to divide the geologic time scale into smaller units
  11. 11. The Geologic Time Scale: Eras Era – a very large unit of geologic timeFour geologic eras1. Precambrian2. Paleozoic3. Mesozoic4. Cenozoic
  12. 12. The Geologic Time Scale: Eras1. Precambrian Time - OLDEST layer - much larger than other eras – 4 billion years - not many fossils so difficult to divide into sections
  13. 13. The Geologic Time Scale: Eras2. Paleozoic Era - Greek word meaning “ancient life” - lasted 325 million years (570 million years ago to 245 million years ago) - large variety of marine, plant, and animalfossils
  14. 14. The Geologic Time Scale: Eras3. Mesozoic Era - Greek for “middle life” - existed for 180 million years - more-complex life forms found like reptiles and birds
  15. 15. The Geologic Time Scale: Eras4. Cenozoic Era - Greek meaning “recent life” - fossils of mammals found in the rocks - earlier forms of life are lower than more-complex forms
  16. 16. The Geologic Time Scale: Periods and EpochsPeriods – shorter time units of each Era - defined by specific fossils - named by location where fossils were firstfound in geologic columnExample: Devonian Period named after Devonshire,England
  17. 17. The Geologic Time Scale: Periods and EpochsEpochs - shorter time units of each era defined bydiversity of fossils - Cenozoic Era has the most diverse anddetailed fossils so easy to divide rock layers fromthis era into periods
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  19. 19. Review Questions Page 346 #1 – 3 Write questions and answer