Geologic time notes


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  • Geologists use the fossil record to determine natural cut-offs Fossils of similar living things are used to represent a specific time period Transitions from one dominant group of organisms to another can mark the division of time periods (Eras, periods, epochs) Other geologic events present in rock layers are also used to mark transitions between time periods: Climate change Extraterrestrial impact Continental drift Change in dominant rock type
  • 4 major eras in Earth’s history Precambrian 4.5 bya-540 mya Paleozoic 540mya- 250 mya Mesozoic 250 mya- 65 mya Cenozoic 65 mya-present
  • Longest Era- spans about 4 billion years or 89% of Earth’s total history Lots of volcanism creating Earth’s crust Some very simple organisms- bacteria, algae, protozoa Oldest Precambrian rocks on Earth date to about 3.5 billion years old Asteroids are thought to have formed at approximately same time as all terrestrial planets- all meteorites that have been recovered from Earth’s surface date to around 4.6 billion years.
  • Paleozoic begins with “Cambrian Explosion”- huge diversity of life Middle of Paleozoic: life made the transition from entirely aquatic to both aquatic and terrestrial Paleozoic ends with the End Permian Mass Extinction- largest loss of life EVER on Earth- over 90% of all living things died out
  • Age of Dinosaurs” Lizards/reptiles are the dominant life form during Mesozoic Birds and mammals also appeared during the Mesozoic
  • With dinosaurs gone, mammals and birds flourished Age of Mammals Mammals became larger Global temperatures cooled Apes and humans appeared Still continues today
  • 5 major mass extinctions 1. End Ordovician - global cooling (57% marine genera) 2. Devonian - 20 degree drop in ocean temperatures (50% marine genera) 3. End Permian - global cooling? Global warming? (90% marine genera, 70% land species) 4. End Triassic - global cooling (48% marine genera) 5. Cretaceous (K/T) - extraterrestrial impact (50% marine genera, 18% terrestrial families)
  • Geologic time notes

    1. 1. Geologic Time A brief history of our planet…
    2. 2. How were these divisions created? <ul><li>fossil record </li></ul><ul><li>Other geologic events </li></ul>
    3. 3. Eon <ul><li>Largest, most general division of time </li></ul><ul><li>4 Eons </li></ul><ul><li>Hadean, Archean, Proterozoic combined are Precambrian Time </li></ul><ul><li>Phanerozoic </li></ul>
    4. 4. Era <ul><li>Each Eon is broken up into Eras </li></ul><ul><li>3 major eras in Earth’s history </li></ul><ul><ul><ul><li>Precambrian Time* 4.5 bya-540 mya </li></ul></ul></ul><ul><ul><ul><li>Paleozoic 540mya- 250mya </li></ul></ul></ul><ul><ul><ul><li>Mesozoic 250 mya- 65 mya </li></ul></ul></ul><ul><ul><ul><li>Cenozoic 65 mya-present </li></ul></ul></ul><ul><ul><ul><li>*Precambrian Time NOT an era, rather several eras combined </li></ul></ul></ul>
    5. 5. Periods <ul><li>Each Era is divided into even more specific blocks of time called periods </li></ul><ul><li>characteristic organisms </li></ul><ul><li>geologic events associated with it </li></ul>
    6. 6. Precambrian time <ul><li>4 billion years (4.5bya-540mya) </li></ul><ul><li>volcanism creating Earth’s crust </li></ul><ul><li>simple organisms- bacteria, algae, protozoa </li></ul><ul><li>Oldest rocks = 3.5 billion years old- So how do we know that Earth is 4.6 billion years old? </li></ul>
    7. 7. Paleozoic Era <ul><li>540-250 mya </li></ul><ul><li>“ Cambrian Explosion” </li></ul><ul><li>Middle of Paleozoic- transition </li></ul><ul><li>End Permian Mass Extinction </li></ul>
    8. 8. Mesozoic Era <ul><li>250-65 mya </li></ul><ul><li>“ Age of Dinosaurs” </li></ul><ul><li>Lizards/reptiles are dominant </li></ul><ul><li>Birds and mammals also appeared </li></ul>
    9. 9. Cenozoic Era <ul><li>65 mya-today </li></ul><ul><li>mammals and birds flourish </li></ul><ul><li>Age of Mammals </li></ul><ul><li>Mammals became larger </li></ul><ul><li>Global temperatures cooled </li></ul><ul><li>Apes and humans appeared </li></ul>
    10. 10. Mass Extinctions <ul><li>5 major mass extinctions </li></ul><ul><li>1. End Ordovician </li></ul><ul><li>2. Devonian </li></ul><ul><li>3. End Permian (aka Permo-Triassic) </li></ul><ul><li>4. End Triassic </li></ul><ul><li>5. Cretaceous (K/T) </li></ul>