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Geologic Time Scale and Introduction to Extinctions

Geologic Time Scale

  • divides 4.5 billion years of Earth history into time periods

  • many divisions are based on extinction events

    • followed by radiation of the new species

  • precambrian is 87% of Earth’s history

Extinction

  • 99% of all species that ever lived are extinct

    • this is considering 3.8 billion years of life on Earth

    • there are still around 1.8 million known species and an estimated 5-15 million species (sources vary) on Earth

  • extinctions are normal

    • extinction is the expected fate, not the rarity

  • the current rate of extinction isn’t normal

    • 1000 times the background rate

Mass Extinction

  • must meet 3 criteria:

    1. 30% of species are extinct

    2. broad range of ecosystems

    3. short/sudden (<1 million years)

  • classified by severity:

    • major: 80-95% of species extinct

    • intermediate: 50% of species extinct

    • minor: 30% of species extinct

  • at least 5 in the Phanerozoic

    1. End-Ordovician

    2. Late Devonian

    3. Permo-Triassic (End-Permian)

    4. End-Triassic

    5. End-Cretaceous (Cretaceous/Paleogene)

  • Permo-Triassic is a major mass extinction, all others are intermediate

Geologic Time Scale and Introduction to Extinctions

Geologic Time Scale

  • divides 4.5 billion years of Earth history into time periods

  • many divisions are based on extinction events

    • followed by radiation of the new species

  • precambrian is 87% of Earth’s history

Extinction

  • 99% of all species that ever lived are extinct

    • this is considering 3.8 billion years of life on Earth

    • there are still around 1.8 million known species and an estimated 5-15 million species (sources vary) on Earth

  • extinctions are normal

    • extinction is the expected fate, not the rarity

  • the current rate of extinction isn’t normal

    • 1000 times the background rate

Mass Extinction

  • must meet 3 criteria:

    1. 30% of species are extinct

    2. broad range of ecosystems

    3. short/sudden (<1 million years)

  • classified by severity:

    • major: 80-95% of species extinct

    • intermediate: 50% of species extinct

    • minor: 30% of species extinct

  • at least 5 in the Phanerozoic

    1. End-Ordovician

    2. Late Devonian

    3. Permo-Triassic (End-Permian)

    4. End-Triassic

    5. End-Cretaceous (Cretaceous/Paleogene)

  • Permo-Triassic is a major mass extinction, all others are intermediate

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