Geologic time

• Eon


  The largest time division, lasting billions of years
• Era


  A subdivision of an eon, scaling hundreds of millions of years
• Period


  A subdivision of an era, lasting tens of millions of years
• Epoch


  A subdivision of a period, lasting around several million years
• The Geologic Time Scale is the stratigraphic history of the Earth
• The Earth is at least 4.6 billion years old
• Humans have only thrived at less than a percent of the Earth's existence
• Geologic Time Scale subdivisions

  • Eons
  • Eras
  • Periods
  • Epochs
• Precambrian Supereon


  Contains three eons that highlight the significant events in the Earth's early life (about ⅞ of the Earth's history)
• Hadean Eon: The Burning Earth

  1. Formation of the moon

  2. Formation of the Earth

  3. Iron Catastrophe

  4. Earth's magnetic field began

  5. First solid continental crust formed

  6. Bombardment events

  7. Continents began to form
• Archaean Eon: The First Rain

  1. First rain fell

  2. Microfossils indicate chemoautotrophs were first living organisms

  3. First atmosphere formed

  4. Extremophiles born

  5. Carbon dissolved and utilised

  6. Vaalbara supercontinent formed
• Proterozoic Eon: The First Freezer

  1. Tectonic plates formed

  2. Prokaryotes formed symbiosis

  3. First extinction

  4. Photosynthetic and energy-converting organisms born

  5. First Ice Age

  6. First extinction of carbon-dependent prokaryotes
• Phanerozoic Eon is an eighth of the whole history of the Earth
• Paleozoic Era: When Life Booms Over

  1. Rodinia supercontinent broke up and formed Pangaea

  2. Plants became dominant land organisms

  3. Animals began to live on land
• Paleozoic Era Periods


  • Cambrian
  • Ordovician
  • Silurian
  • Devonian
  • Carboniferous
  • Permian
• Cambrian Period marked the Cambrian Explosion, creating biodiversity
• Ordovician Period saw the first extinction of eukaryotes
• Silurian Period saw the evolution of the first freshwater fish
• Devonian Period is known as the Age of the Fish
• Carboniferous Period saw the development of tropical swamps and the first reptiles
• Permian Period saw all separate continents form Pangaea
• Carboniferous


  Meaning "to carry", coal-bearing
• Rocks dated in this period are varied
• Rock types from the Carboniferous period

  • Limestone
  • Sandstone
  • Shale
  • Coal
• Coal deposits dominate other rock deposits from the Carboniferous period
• Average global temperatures were exceedingly high during the Carboniferous period
• Tropical swamps were developed during the Carboniferous period
• Lignin-laden plants and trees grew taller and became more numerous, including seed ferns, during the Carboniferous period
• Amniotic eggs were developed during the Carboniferous period, allowing amphibians to go farther inland and become the dominant vertebrate
• The first reptiles appeared during the Carboniferous period
• Because of the cool global temperatures, rainforests collapsed and a third Ice Age came during the Carboniferous period
• Permian Period


  Named after the Russian region of Perm
• All separate continents formed Pangaea during the Permian period
• The major marker of the Permian period is the Ural mountains (where Perm itself is located)
• Reptiles dominated the scene during the Permian period, with early dinosaurs such as Dimetrodon and Edaphosaurus evolving and dominating Pangaea
• The first cone-bearing plants (true conifers and cycads) and the ginkgo (sometimes written as gingko) evolved and thrived in the new landscape of the Permian period
• Near the end of the Permian period, Pangaea became drier, thus creating more deserts
• More vertebrates dominated the scene during the Permian period, such as Scutosaurus and Gorgonopsids
• Eventually, a third extinction came during the Permian period, which is known as The Great Dying
• Mesozoic Era


  Also known as the Age of Reptiles or Age of the Dinosaurs, it is the period where the Earth began to recover from its third extinction