Mass extinctions on Earth


    In news

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

    About the extinctions

    • 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.
      • More than 99 per cent of all organisms that have ever lived on Earth are extinct.
      • As new species evolve to fit ever-changing ecological niches, older species fade away. But the rate of extinction is far from constant.
    • Several theories: There have been several theories behind each of the mass extinction and with advances in new technologies; researchers have been uncovering more intricate details about these events.
    • Other great mass extinctions: Before the Cretaceous mass extinction known for wiping out non-avian dinosaurs, the Earth had witnessed four other great mass extinctions.

    What are these mass extinctions?

    • Rapid decrease in biodiversity: An extinction event is a widespread and rapid decrease in the biodiversity on Earth.
    • Biotic crisis: It is also known as a mass extinction or biotic crisis.
    • Abundance of multicellular organisms: Such an event is identified by a sharp change in the diversity and abundance of multicellular organisms.
    • Increase in rate of extinction: It occurs when the rate of extinction increases with respect to the rate of speciation.
    • Uneven rate: Extinction occurs at an uneven rate.
    • The Great Oxidation Event: which occurred around 2.45 billion years ago, was probably the first major extinction event.
    • New forms of life: Though mass extinctions are deadly events, they open up the planet for new forms of life to emerge.

    Factors affecting the extinction

    • Change in ocean circulation pattern and climate cooling: 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.
      • They also noticed a lack of oxygen or anoxia in deep oceans during the period.
      • Upper-ocean oxygenation in response to cooling was anticipated because atmospheric oxygen preferentially dissolves in cold waters.
      • However, we were surprised to see expanded anoxia in the lower ocean since anoxia in Earth’s history is generally associated with volcanism-induced global warming.
    • Major changes in Earth’s carbon cycle: such as large igneous province eruptions, huge volcanoes that flooded hundreds of thousands of square miles with lava. These eruptions ejected massive amounts of heat-trapping gases such as carbon dioxide into the atmosphere, enabling runaway global warming and related effects such as ocean acidification and anoxia, a loss of dissolved oxygen in the water.
    • Humans to be blamed: Ever since the beginning of the pollutant-pumping industrial revolution in 1760, humans have been the main contributor to Earth’s current environmental crisis.
      • From greenhouse gas emissions and ozone depletion to deforestation, plastic pile-up and the illegal animal trade, humans have actively stripped the world of some species and threatened many more.
    • Pandemic perspective: 2020’s lockdowns have led to a 17% global decrease in carbon emissions and a 20% fall in nitrogen oxide levels, according to NASA. Waterways cleared up, and animals were seen venturing into cities and towns around the world. 

    The other big extinction events

    • Ordovician-Silurian extinction – 444 million years ago
      • The Ordovician period, from 485 to 444 million years ago, was a time of dramatic changes for life on Earth. This event killed an estimated 85 percent of all species.
      • Over a 30-million-year stretch, species diversity blossomed, but as the period ended, the first known mass extinction struck.
      • At that time, massive glaciation locked up huge amounts of water in an ice cap that covered parts of a large south polar landmass.
      • The icy onslaught may have been triggered by the rise of North America’s Appalachian Mountains.
      • The large-scale weathering of these freshly uplifted rocks sucked carbon dioxide out of the atmosphere and drastically cooled the planet.
      • As a result, sea levels plummeted by hundreds of feet. Creatures living in shallow waters would have seen their habitats cool and shrink dramatically, dealing a major blow.
      • The event took its hardest toll on marine organisms such as corals, shelled brachiopods, eel-like creatures called conodonts, and the trilobites.

    • Late Devonian extinction – 383-359 million years ago
      • Starting 383 million years ago, this extinction event eliminated about 75 percent of all species on Earth over a span of roughly 20 million years.
      • In several pulses across the Devonian, ocean oxygen levels dropped precipitously, which dealt serious blows to conodonts and ancient shelled relatives of squid and octopuses called goniatites.
      • The worst of these pulses, called the Kellwasser event, came about 372 million years ago.
      • Rocks from the period in what’s now Germany show that as oxygen levels plummeted, many reef-building creatures died out, including a major group of sea sponges called the stromatoporoid.
      • The faster rocks weathered, the more excess nutrients flowed from land into the oceans. The influx would have triggered algae growth, and when these algae died, their decay removed oxygen from the oceans to form what are known as dead zones.
      • In addition, the spread of trees would have sucked CO2 out of the atmosphere, potentially ushering in global cooling.
      • The slowdown may have been caused by the global spread of invasive species, as high sea levels let creatures from previously isolated marine habitats mix and mingle, which let ecosystems around the world homogenize.

    • Permian-Triassic extinction – 252 million years ago
      • Some 252 million years ago, life on Earth faced the “Great Dying”: the Permian-Triassic extinction.
      • The cataclysm was the single worst event life on Earth has ever experienced.
      • Over about 60,000 years, 96 per cent of all marine species and about three of every four species on land died out.
      • The world’s forests were wiped out and didn’t come back in force until about 10 million years later.
      • Of the five mass extinctions, the Permian-Triassic is the only one that wiped out large numbers of insect species.
      • The extinction’s single biggest cause is the Siberian Traps, an immense volcanic complex that erupted more than 720,000 cubic miles of lava across what is now Siberia.
      • The eruption triggered the release of at least 14.5 trillion tons of carbon, more than 2.5 times what’d be unleashed if every last ounce of fossil fuel on Earth were dug up and burned.
      • As temperatures rose, rocks on land weathered more rapidly, hastened by acid rain that formed from volcanic sulfur.

    • Triassic-Jurassic extinction – 201 million years ago
      • Life took a long time to recover from the Great Dying, but once it did, it diversified rapidly.
      • Different reef-building creatures began to take hold, and lush vegetation covered the land, setting the stage for a group of reptiles called the archosaurs: the forerunners of birds, crocodilians, pterosaurs, and the non-avian dinosaurs.
      • But about 201 million years ago, life endured another major blow: the sudden loss of up to 80 percent of all land and marine species.
      • At the end of the Triassic, Earth warmed an average of between 5 and 11 degrees Fahrenheit, driven by a quadrupling of atmospheric CO2 levels.
      • This was probably triggered by huge amounts of greenhouse gases from the Central Atlantic Magmatic Province, a large igneous province in central Pangaea, the supercontinent at the time.
      • The uptick in CO2 acidified the Triassic oceans, making it more difficult for marine creatures to build their shells from calcium carbonate.
      • On land, the dominant vertebrates had been the crocodilians, which were bigger and far more diverse than they are today. Many of them died out.
      • In their wake, the earliest dinosaurs—small, nimble creatures on the ecological periphery rapidly diversified.

    • Cretaceous-Paleogene extinction – 66 million years ago
      • The Cretaceous-Paleogene extinction event is the most recent mass extinction and the only one definitively connected to a major asteroid impact.
      • Some 76 per cent of all species on the planet, including all nonavian dinosaurs, went extinct.
      • The massive impact—which left a crater more than 120 miles wide-flung huge volumes of dust, debris, and sulfur into the atmosphere, bringing on severe global cooling.
      • Wildfires ignited any land within 900 miles of the impact, and a huge tsunami rippled outward from the impact.
      • Overnight, the ecosystems that supported nonavian dinosaurs began to collapse.
      • Global warming fueled by volcanic eruptions at the Deccan Flats in India may have aggravated the event.

    Extinction today (Sixth mass extinction)

    • Biodiversity crisis: Earth is currently experiencing a biodiversity crisis.
    • Various human factors: Recent estimates suggest that extinction threatens up to a million species of plants and animals, in large part because of human activities such as deforestation, hunting, and overfishing.
    • Spread of invasive species: Other serious threats include the spread of invasive species and diseases from human trade, as well as pollution and human-caused climate change.
    • Extinctions are occurring hundreds of times faster: If all species currently designated as critically endangered, endangered, or vulnerable go extinct in the next century, and if that rate of extinction continues without slowing down, we could approach the level of mass extinction in as soon as 240 to 540 years.
    • Climate change presents a long-term threat: Humans’ burning of fossil fuels has let us chemically imitate large igneous provinces, through the injection of billions of tons of carbon dioxide and other gases into Earth’s atmosphere each year.

    Various steps to be taken to prevent the mass extinctions

    • Humans can be the driving force: The world is awash with scientists, conservationists and environmentalists working in the laboratory, in conservation areas and in political battlegrounds to protect endangered species.
    • Legislation: From tackling global pollution emissions in the 2016 Paris Agreement to the U.K.’s Global Resource Initiative that combats deforestation, legislation will always be at the forefront of the fight against mass extinction.
    • Regulating wildlife markets: In the wake of the current pandemic, wildlife markets have been thrust into the spotlight as not only being environmentally irresponsible, but potentially dangerous to human health through zoonotic diseases that jump from animals to humans such as COVID-19. These markets, trading live exotic animals or products derived from them, are found throughout the world.
    • Monitoring species population: One of the best ways to help prevent species from becoming extinct is to monitor their populations and identify any problems before it’s too late to help. Currently camera traps and surveys conducted on foot or from aircraft are the main method of data collection.
    • Saved by cloning: Another potential solution to combat extinction could be to clone species. In 2021, scientists revealed they had successfully cloned a black-footed ferret from an animal that had died more than 30 years ago.
      • Native to North America, these small mammals were thought to be extinct until a small colony was found in the early 1980s, which were entered into a breeding program and reintroduced around the United States.