Earth's History

• Stratified


  Successive beds of sediments that have been solidified
• Stratigraphy


  Study of layers of rocks and relationship
• Sedimentary


  From older rocks; accumulation of sediments
• Dating techniques


  • Relative - based on rock sequence = older rocks at the bottom layers
  • Absolute - gives the actual age of the rock or the period of events. Used radioactive decay
• Radioactive dating


  Most accurate method of absolute dating
• Carbon dating


  One of the best radiometric techniques
• Index fossils


  Establish the age of rock layers, act as a bookmark to determine the age or period of rock layers
• Index fossils


  • Ammonites, trilobites, graptolites, protista (marine fossils), Viviparus glacialis (Pleistocene)
• Characteristics of index fossils

  • Abundance, widespread distribution, distinct identifiable features, existed only in a short yet specific span of geologic time
• How fossils form


  1. Mummification

  2. Amber

  3. Tar seeps

  4. Freezing

  5. Petrification
• In very rare cases, DNA has been recovered from amber
• Types of fossils


  • Imprint carbonized leaf
  • Mold and cast of trilobite
  • Fossilized dung or waste of ancient animals
• Geologic time scale


  Model of Earth's history that describes the order of events and their duration
• Eras of the geologic time scale

  • Precambrian
  • Paleozoic
  • Mesozoic
  • Cenozoic
• Precambrian


  • Makes up 88% of Earth's history, not enough record, rocks are extremely old
• Paleozoic


  • Pangea was formed, abundant fossil records, trilobites flourished, end of Permian - mass extinction
• Mesozoic


  • Rich fossil records, age of reptiles - dinosaurs dominated, flowering plants appeared, ended with extinction of dinosaurs
• Cenozoic


  • Recent life, age of mammals, dramatic climate changes, present time belongs to Quaternary period