Surviving an extinction level event | Khan Academy

Surviving an Extinction Level Event

Mass Extinctions

  • Life on Earth has experienced multiple mass extinctions followed by periods of recovery.

  • Extinction events lead to a significant decrease in species diversity and abundance.

  • Geologists and paleontologists analyze extinctions utilizing sedimentary rock and fossil records to understand past events.

Five Major Extinction Events

  1. Ordovician-Silurian Extinction (442 MYA)

    • Characterized by the extinction of small marine organisms.

  2. Late Devonian Extinction (365 MYA)

    • Many tropical marine species experienced extinction during this time.

  3. End-Permian Extinction (251 MYA)

    • Known as the most catastrophic event, resulting in the extinction of approximately 95% of marine species and 70% of terrestrial species.

  4. End-Triassic Extinction (201 MYA)

    • This event removed other vertebrates, paving the way for dinosaurs to thrive.

  5. K-T (Cretaceous-Paleogene) Extinction (66 MYA)

    • Led to the extinction of the non-avian dinosaurs, likely triggered by an asteroid impact.

K-T Extinction and the Chicxulub Crater

  • An object, comparable in size to Mount Everest, struck Earth near the Yucatán Peninsula.

  • The impact created a crater approximately the size of Belgium, resulting in massive fires, climatic changes, and ecosystem collapse.

  • Most dinosaurs, along with around 75% of all species, went extinct as a result.

  • The presence of iridium in rock layers has provided crucial evidence pointing towards an asteroid or comet impact.

  • The Chicxulub crater was identified as the impact site in 1991.

Possible Causes of Mass Extinctions

  • Volcanic activity that releases CO₂ can lead to global warming and diminished photosynthesis.

  • Rapid shifts in climate conditions.

  • Impacts from asteroids or comets.

  • Ocean anoxia (low oxygen levels) affecting marine life.

  • Changes in continental drift that alter ocean currents.

  • Some researchers propose that previous extinctions were driven by heightened levels of CO₂ and methane, which may have resulted in toxic conditions for oceanic organisms.

A Sixth Mass Extinction?

  • Numerous scientists argue that a sixth extinction is currently in progress, primarily due to human activities.

  • Factors like habitat destruction, climate change, and pollution are leading to a significant loss of species.

  • This potential extinction began about 50,000 years ago coinciding with human expansion into new continents.

  • It is predicted that one in four mammal species and one in eight bird species are at risk of extinction.

  • If current trends continue, it is estimated that 50% of all known species may disappear by the end of this century.