Mass Extinction | 08 Nov 2021

Why in News

Recently, a paper published in the international journal Nature Geoscience has come up with a new reason behind the first mass extinction, also known as the Late Ordovician mass extinction.

• It notes that the cooling climate likely changed the ocean circulation pattern. This caused a disruption in the flow of oxygen-rich water from the shallow seas to deeper oceans, leading to a mass extinction of marine creatures.

Key Points

• Mass Extinction (Meaning):
  
  • A mass extinction event is when species vanish much faster than they are replaced.
  • This is usually defined as about 75% of the world's species being lost in a 'short' amount of geological time - less than 2.8 million years.
• Mass Extinctions So Far:
  
  • First Mass Extinction: The Ordovician mass extinction that occurred about 445 million years ago killed about 85% of all species.
  • Second Mass Extinction: The Devonian mass extinction (about 375 million years ago) wiped out about 75% of the world’s species.
  • Third Mass Extinction: The Permian mass extinction (about 250 million years ago) also known as the Great Dying caused the extinction of over 95% of all species.
  • Fourth Mass Extinction: The Triassic mass extinction (about 200 million years ago) eliminated about 80% of Earth’s species, including some dinosaurs.
  • Fifth Mass Extinction: This Cretaceous mass extinction (about 65 million years ago) is known for wiping out non-avian dinosaurs.

• About the Latest Findings:
  
  • New Explanations: There have been several theories behind each mass extinction and with advances in new technologies, researchers have been uncovering more intricate details about these events.
  • Traditional Thought: For decades, the prevailing school of thought was that volcanism-induced global warming causes the oceans to lose oxygen and thus impact marine habitability, potentially destabilising the entire ecosystem.
  • New School of Thought: In recent years, mounting evidence points to several episodes in the Earth’s history when oxygen levels also dropped in cooling climates.
    
    • Ordovician climate and marine biogeochemical cycles during that period showed “seafloor and upper-ocean oxygenation in response to ongoing global cooling.”
      
      • This led to deep-sea anoxia affecting ocean circulation.
    • Thus, the paper concludes that climate cooling may have led to changes in nutrient cycling, primary producer communities which ultimately drove the Late Ordovician mass extinction.
• Ongoing Sixth Mass Extinction and Impact:
  
  • Sixth Mass Extinction:
    
    • Some researchers have pointed out that we are currently experiencing a sixth mass extinction as the result of human-induced climate change (referred to as the Anthropocene extinction).
      
      • Currently, only an estimated 2% of all of the species that ever lived are alive but the absolute number of species is greater than ever before.
    • It is described as the most serious environmental problem since the loss of species will be permanent.
      
      • The loss of species has been occurring since human ancestors developed agriculture over 11,000 years ago. Since then, the human population has increased from about 1 million to 7.7 billion.
  • Possible Impact:
    
    • The extinction of the species causes tangible impact such as in the form of a loss in crop pollination and water purification.
    • Further, if a species has a specific function in an ecosystem, the loss can lead to consequences for other species by impacting the food chain.
    • The effects of extinction are expected to worsen the genetic and cultural variability which would change entire ecosystems.
      
      • When genetic variability and resilience is reduced, its contribution to human welfare may be lost.

Source: IE