Geologic Time and Earth's Biological History

• Geologic Time Scale


  A chronologic schema relating to time that is used by geologists, palaeontologists and other Earth scientists to describe the timing and relationships between events that have occurred during the history of the Earth

  
• Divisions of Geologic Time

  • Eon: half a billion years or more
  • Era: several hundred million years
  • Period: one hundred million years
  • Epoch: tens of million of years
  • Age: million of years

  
• We are living in the Phanerozoic Eon, Cenozoic Era, Quaternary Period, Holocene Epoch

  
• Eons


  • Precambrian
  • Phanerozoic

  
• Eras


  • Paleozoic
  • Mesozoic
  • Cenozoic

  
• Periods


  • Cambrian
  • Ordovician
  • Silurian
  • Devonian
  • Carboniferous
  • Permian
  • Triassic
  • Jurassic
  • Cretaceous
  • Paleogene
  • Neogene
  • Quaternary

  
• Epochs


  • Paleocene
  • Eocene
  • Oligocene
  • Miocene
  • Pliocene
  • Pleistocene
  • Holocene

  
• Precambrian time covers approximately 88% of Earth's history

  
• Precambrian Eras


  • Hadean
  • Archean
  • Proterozoic

  
• Precambrian


  • Earth formed
  • Life arose
  • First tectonic plates arose and began to move
  • Eukaryotic cells evolved
  • Atmosphere became enriched in oxygen
  • Complex multicellular organisms, including the first animals, evolved

  
• Stromatolites


  Layered mats formed by colonies or groups of cyanobacteria (blue-green algae thought to be one of the earliest life forms on Earth)
• Most Precambrian organisms had soft bodies which looked like modern jellyfish and worms
• Invertebrates (animals with no backbone) appeared near the end of the Precambrian Time

  
• Mass extinction event ended the Precambrian Time
• Paleozoic Era


  Age of the Invertebrates

  
• Much of the limestone quarried for building and industrial purposes, as well as the coal deposits of western Europe and the eastern United States, were formed during the Paleozoic
• The Cambrian period is the 1st period of the Paleozoic Era

  
• Cambrian Period


  Age of the Trilobites
• Explosion of life in the oceans began during the Paleozoic Era
• Most of the continents were covered in warm, shallow seas during the Paleozoic

  
• Dominant Paleozoic animals


  • Trilobites
  • Fish
  • Amphibians

  
• Early land plants including mosses, ferns and cone-bearing plants appeared during the Paleozoic
• The early coal forming forests were also formed during the Paleozoic
• The Appalachian mountains were formed during the Paleozoic
• The end of the Paleozoic era is called the "Age of Amphibians"

  
• The Permian period was the last period of the Paleozoic Era

  
• 90% of Earth's species became extinct at the end of the Permian period due to volcanism in Siberia
• Trilobites


  Lived in Earth's ancient seas and were extinct before the dinosaurs came into existence

  
• Brachiopods


  Marine animals that resemble clams
• Early fish did not have jaws
• Some species of sharks were in existence during the Paleozoic
• Cone bearing plants, ferns and mosses were early land plants that appeared during the Paleozoic
• The largest mass extinction event in Earth's history occurred at the end of the Paleozoic Era
• Carboniferous Period


  • Ice covers the southern hemisphere
  • Coal swamps formed along equator
  • Lizards and winged insects first appear
• Permian


  • Last period of the Paleozoic
  • Pangea forms
  • Reptiles spread across continents
  • The Appalachians rise
  • 90% of Earth's species become extinct due to volcanism in Siberia
• Trilobites


  • Lived in Earth's ancient seas
  • Extinct before the dinosaurs came into existence
  • Cambrian Period is known as the "Age of the Trilobites"

  
• Early Fish


  • Did not have jaws
  • Some species of sharks were in existence
• Frilled Shark


  • Found in Japan in January 2007
  • Considered a "living fossil"
• Early Land Plants


  • Cone bearing plants
  • Ferns
  • Mosses
• Paleozoic Era


  • At the end, the largest mass extinction in history wiped out approximately 90% of all marine animal species and 70% of land animals
  • Possible causes: Lowering of sea levels when the continents were rejoined as Pangaea, Increased volcanic activity, Climate changes – cooler climate