Sixth mass extinction

Why in news?

• Sixth mass extinction event in progress, claims study; blames human activities
• A new study has now added that Earth could have already lost about 7.5 and 13 per cent of its total species.

Five mass extinctions:

• First Mass Extinction: 444 million years ago
  • 86% of species lost, happened during Ordovician period
  • Severe ice age that lowered sea levels, possibly triggered by the uplift of the Appalachians.
  • The newly exposed silicate rock sucked CO2 out of the atmosphere, chilling the planet.
• Second Mass Extinction: 383-359 million years ago
  • 75% of species lost, happened during late Devonian period
  • With the emergence of land plants, their deep roots stirred up the earth, releasing nutrients into the ocean. This might have triggered algal blooms which sucked oxygen out of the water, suffocating bottom dwellers like the trilobites.
• Third Mass Extinction:252 million years ago
  • 96% of species lost, happened during Permian
  • A cataclysmic eruption near Siberia blasted CO2 into the atmosphere. Methanogenic bacteria responded by belching out methane, a potent greenhouse gas.
  • Global temperatures surged while oceans acidified and stagnated, belching poisonous hydrogen sulfide.
• Fourth Mass Extinction:201 million years ago
  • 80% of species lost, happened during Triassic
  • No clear causes have been found.
• Fifth Mass Extinction: 66 million years ago
  • 76% of all species lost, happened during Cretaceous.
  • Volcanic activity and climate change along with asteroid species

Sixth mass extinction:

• Mass extinction refers to a substantial increase in the degree of extinction or when the Earth loses more than three-quarters of its species in a geologically short period of time.
• The Holocene extinction, otherwise referred to as the sixth mass extinction or Anthropocene extinction, is an ongoing extinction event of species as a result of human activity.
• The study said that 150,000 to 260,000 species lost (7.5 to 13 per cent of its two million species) have gone extinct in the last 500 years.
  • 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.
• The research blames human activities for the rapid deterioration of the number of species in the planet.
• The current extinction is not a new phenomenon and has been going on since the 16th century.

Impacts:

• 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.
• When the number of individuals in a population or species drops too low, its contributions to ecosystem functions and services become unimportant.
• 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.

PRACTICE QUESTION:

The terms ‘Cretaceous’ and ‘Permian’, are associated with:

(a) Organisms inhabiting the seafloor

(b) Geological time scale

(c) Ancient cave architecture

(d) Zoonotic pathogens

Answer