5.4 Mass extinctions and their impact on biodiversity

Earth's history is marked by five major mass extinctions, where vast numbers of species vanished rapidly. These events, like the End-Permian "Great Dying" and the dinosaur-killing End-Cretaceous, reshaped life on our planet.

Mass extinctions were caused by asteroid impacts, volcanic eruptions, and climate change. They drastically reduced biodiversity, but also paved the way for new evolutionary paths. Today, human activities are driving a biodiversity crisis that could lead to a sixth mass extinction.

Mass Extinctions

Mass extinctions in Earth's history

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Top images from around the web for Mass extinctions in Earth's history

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  Charting Earth’s (Many) Mass Extinctions — Blog of the Long Now View original

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• Events characterized by rapid, global decrease in biodiversity with significant proportion of species going extinct within geologically short time period
  • Typically 75% or more of all species go extinct during mass extinction event
• The Big Five mass extinctions in Earth's history
  • End-Ordovician (444 million years ago)
  • Late Devonian (372 million years ago)
  • End-Permian (252 million years ago)
    • Most severe mass extinction, known as "The Great Dying"
    • Estimated 95-96% of marine species and 70% of terrestrial vertebrate species went extinct
  • End-Triassic (201 million years ago)
  • End-Cretaceous (66 million years ago)
    • Famous for extinction of non-avian dinosaurs (Tyrannosaurus rex, Triceratops)

Causes of mass extinctions

• Asteroid impacts
  • Cause global cooling due to dust and aerosols blocking sunlight
  • Trigger wildfires, tsunamis, and acid rain
  • Chicxulub impact at End-Cretaceous boundary
• Volcanic eruptions
  • Large-scale eruptions release vast amounts of ash, dust, and greenhouse gases
    • Ash and dust block sunlight, causing global cooling
    • Greenhouse gases lead to global warming
  • Siberian Traps eruptions at End-Permian boundary
• Climate change
  • Rapid changes in temperature disrupt ecosystems (global warming or cooling)
  • Changes in ocean circulation patterns affect nutrient distribution and marine life
  • Global cooling during End-Ordovician extinction

Impact on biodiversity and recovery

• Mass extinctions drastically reduce global biodiversity
  • Many species, including entire families or orders, go extinct (ammonites, trilobites)
  • Ecosystems disrupted and food webs collapse
• Recovery after mass extinctions is gradual
  1. Surviving species adapt to new niches and evolve into new forms
  2. Biodiversity slowly increases as new species emerge
  3. Recovery can take millions of years
• Mass extinctions alter course of evolution
  • Surviving lineages radiate and diversify, leading to new evolutionary paths
  • Rise of mammals after End-Cretaceous extinction

Current biodiversity crisis

• Current biodiversity crisis characterized by rapid species loss due to human activities
  • Habitat destruction, fragmentation, and degradation (deforestation, urbanization)
  • Overexploitation of resources (overfishing, poaching)
  • Pollution and climate change (plastic waste, greenhouse gas emissions)
  • Invasive species introduction (rats on islands, zebra mussels in lakes)
• Current extinction rates estimated to be 100 to 1,000 times higher than background extinction rate
  • Background extinction rate: 1-5 species per year
  • Current extinction rate: 100-1,000 species per year
• If current trends continue, Earth may experience sixth mass extinction
  • Referred to as Anthropocene or Holocene extinction
  • Unique in being primarily driven by human activities rather than natural causes
• Consequences of current biodiversity crisis
  • Loss of ecosystem services (pollination, water filtration)
  • Reduced resilience to environmental changes
  • Potential cascading effects on human well-being and global economy