Mass Extinctions in Earth History

Overview of Earth's Mass Extinction Events

Earth's geological history is marked by five major mass extinction events, each causing severe biodiversity loss due to drastic environmental and geological changes.

The Ordovician Extinction

• Extinction Magnitude: $86\%$ of species died out.

• Timing and Occurrence: Occurred approximately $440\text{ million years ago}$.

• Primary Causes:

  • A rapid drop in global temperatures and altered climate patterns.

  • Organisms were unable to adapt to the colder temperatures.

  • Widespread destruction of marine habitats.

• Hardest-Hit Organisms: Corals and deep-shelf bottom-dwelling creatures, such as trilobites.

The Devonian Extinction

• Extinction Magnitude: $75\%$ of species died out.

• Timing and Duration: Occurred approximately $365\text{ Mya}$ (million years ago) and lasted for about $20\text{ million years}$.

• Primary Causes:

  • Rapid expansion of terrestrial land plants absorbed massive quantities of atmospheric carbon dioxide ($CO_2$).

  • The decline in greenhouse gases triggered global cooling, severely affecting both terrestrial environments and oceans.

• Hardest-Hit Organisms: Corals, jawless fish, armored fish, and hard-shelled marine creatures such as ammonites.

The Permian Extinction

• Extinction Magnitude: $96\%$ of species died out, making it the largest mass extinction event in Earth's history.

• Timing and Duration: Occurred approximately $250\text{ Mya}$ and lasted for about $2.8\text{ million years}$.

• Primary Causes:

  • Major volcanic eruptions triggered rapid global warming.

  • Dramatic and catastrophic shifts in ocean chemistry.

• Hardest-Hit Organisms: Corals, early terrestrial tetrapods, insects, and trilobites.

The Triassic Extinction

• Extinction Magnitude: $80\%$ of species died out.

• Timing and Duration: Occurred approximately $200\text{ Mya}$ and lasted between $2\text{ to }3\text{ million years}$.

• Primary Causes:

  • Tectonic activity and shifting continents triggered widespread volcanic eruptions.

  • Eruptions caused rapid global warming, along with dramatic changes to ocean chemistry and sea levels.

• Hardest-Hit Organisms: Amphibians, reptiles, corals, and ammonites.

The Cretaceous Extinction

• Extinction Magnitude: $76\%$ of species died out.

• Timing and Duration: Occurred approximately $65\text{ Mya}$ and lasted for about $2.5\text{ million years}$.

• Primary Causes:

  • Intense volcanic activity combined with a massive asteroid impact.

  • Airborne dust and debris blocked solar radiation, halting photosynthesis.

  • The death of plant life caused a complete collapse of global food chains.

• Hardest-Hit Organisms: Plants, non-avian dinosaurs, large terrestrial animals, and mollusks.

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