Introduction

Extinction events are periods in Earth’s history when large numbers of species vanish in a relatively short time. These events have shaped the diversity of life on our planet, influencing which species survive and evolve. Understanding extinction events helps scientists learn about Earth’s past environments, the impact of natural disasters, and the resilience of life. Extinction is a natural process, but mass extinctions are rare and dramatic, often caused by extraordinary circumstances.

Main Concepts

What Is Extinction?

  • Extinction occurs when a species no longer exists anywhere on Earth.
  • Background extinction rate refers to the normal rate of species loss due to environmental changes, competition, or predation.
  • Mass extinction is when at least 75% of species disappear within a geologically short time (usually less than 2 million years).

Major Extinction Events

Scientists recognize five major mass extinction events, known as the “Big Five”:

  1. Ordovician-Silurian Extinction (about 443 million years ago)

    • Up to 85% of marine species disappeared.
    • Likely caused by rapid climate change and glaciation.

  2. Late Devonian Extinction (about 372 million years ago)

    • Around 75% of species lost, especially marine life.
    • Causes may include asteroid impacts, volcanic activity, and changes in sea level.

  3. Permian-Triassic Extinction (about 252 million years ago)

    • The largest extinction event; over 90% of species vanished.
    • Massive volcanic eruptions in Siberia released gases, altering climate and ocean chemistry.

  4. Triassic-Jurassic Extinction (about 201 million years ago)

    • About 80% of species lost.
    • Possible causes: volcanic eruptions, climate change, and asteroid impacts.

  5. Cretaceous-Paleogene (K-Pg) Extinction (about 66 million years ago)

    • Famous for ending the reign of dinosaurs.
    • Evidence points to a large asteroid impact near the Yucatán Peninsula (Chicxulub crater).

Causes of Extinction Events

  • Asteroid impacts: Can cause global fires, darkness, and cooling.
  • Volcanic eruptions: Release gases and ash, changing climate and ocean acidity.
  • Climate change: Rapid shifts in temperature or sea level can disrupt ecosystems.
  • Ocean anoxia: Loss of oxygen in oceans, often linked to volcanic activity.
  • Human activity: In recent times, habitat destruction, pollution, and overhunting have accelerated extinctions.

Effects on Life and Evolution

  • Biodiversity loss: Many unique species disappear forever.
  • Evolutionary opportunities: Surviving species may evolve rapidly to fill empty niches.
  • Recovery periods: Ecosystems can take millions of years to recover.

Controversies and Debates

  • Single vs. multiple causes: Scientists debate whether mass extinctions are triggered by one event (like an asteroid) or a combination (volcanoes, climate change).
  • Human-driven extinction: Some argue that current species loss rates indicate a “Sixth Mass Extinction” caused by human activities. Others believe more evidence is needed.
  • Fossil record gaps: Incomplete fossil records make it difficult to determine exactly how and when species disappeared.
  • Resilience of life: Some researchers question how quickly ecosystems can recover and whether some groups are more vulnerable than others.

Latest Discoveries

  • New insights on Permian-Triassic extinction: A 2021 study published in Nature Geoscience found that volcanic activity in Siberia released massive amounts of greenhouse gases, causing severe global warming and ocean acidification, which led to the extinction of most marine species.
  • Modern extinction rates: Recent research (Ceballos et al., 2020, PNAS) shows that current extinction rates are much higher than background rates, suggesting humans are driving a new mass extinction.
  • Exoplanet discoveries: The first exoplanet was discovered in 1992, expanding our understanding of planetary systems. While not directly linked to extinction events, studying exoplanets helps scientists explore how life might survive or perish under different conditions.

Project Idea

Create a Timeline and Model of a Mass Extinction Event

  • Research one of the “Big Five” mass extinction events.
  • Build a timeline showing key events before, during, and after the extinction.
  • Make a 3D model or poster illustrating the causes, effects on species, and recovery period.
  • Include recent scientific findings and controversies about the event.
  • Present your project to your class, explaining how scientists study extinction events and why they matter today.

Conclusion

Extinction events are crucial chapters in Earth’s history, shaping the evolution and diversity of life. They are caused by extraordinary natural disasters, rapid environmental changes, and, more recently, human activities. Studying these events reveals how life responds to challenges and recovers over time. Recent research continues to uncover new details about past extinctions and warns us about the consequences of current species loss. Understanding extinction events helps us protect biodiversity and appreciate the resilience of life on our planet.

Recent Reference

  • Ceballos, G., Ehrlich, P.R., Raven, P.H. (2020). “Vertebrates on the brink as indicators of biological annihilation and the sixth mass extinction.” Proceedings of the National Academy of Sciences, 117(24), 13596-13602. Link
  • Black, B.A., et al. (2021). “Global climate change and the Siberian Traps: Evidence from the end-Permian extinction.” Nature Geoscience, 14, 1–6. Link