Earth Facing Sixth Mass Extinction Crisis, And It's Caused By Humans This Time: Scientists

Five mass extinctions have occurred on Earth in the past. All of them were caused by natural phenomena.

A cardboard reads 'Mass extinction: insects, fish, birds.. Glyphosate, pesticides: we continue ?' (Photo: Getty)

New Delhi: Ever since life began on Earth, there have been five events of mass biodiversity extinction. A mass extinction event is when species vanish much faster than they are replaced, and is usually defined as about 75 per cent of the world's species being lost in a 'short' amount of geological time (less than 2.8 million years), according to an article on the website of the National History Museum, located in London. 

The five mass extinctions that have occurred on Earth include the Ordovician Mass Extinction, Devonian Mass Extinction, Permian Mass Extinction, Triassic-Jurassic Mass Extinction, and Cretaceous-Tertiary (or the K-T) Mass Extinction. All these extinction events were caused by natural phenomena. 

Now, many experts warn that a Sixth Mass Extinction crisis is underway. However, this time, a mass extinction will be caused entirely by human activities, according to scientists.

A team of biologists from the University of Hawaii at Mānoa, United States, and the Muséum National d'Histoire Naturelle in Paris, France, performed a comprehensive assessment of evidence of this ongoing extinction event. The findings of the study were recently published in the journal, Biological Reviews.

Robert Cowie, the lead author of the study, said that drastically increased rates of species extinctions and declining abundances of many animal and plant populations are well documented, yet some deny that these phenomena amount to mass extinction, according to a statement issued by the University of Hawaii at Mānoa.

'Biased View' Of The Ongoing Extinction Crisis

Cowie said that a biased view of the crisis is responsible for this denial. The biased view focuses on mammals and birds and ignores invertebrates, which constitute the great majority of the biodiversity, he explained.

The researchers extrapolated estimates obtained from land snails and slugs, and estimated that Earth could already have lost between 7.5 and 13 per cent of the 2 million known species on the planet, since the year 1500. This means as many as 1,50,000 to 2,60,000 species could have gone extinct in over 500 years, according to the study.

Quoting Cowie, the statement said that including vertebrates was key to confirming that the world is indeed witnessing the onset of the Sixth Mass Extinction in Earth's history.

Aquatic And Terrestrial Species Affected Differently

The situation is different for terrestrial and aquatic organisms. Marine species gave significant threats. However, there is no evidence that the crisis is affecting the oceans to the same extent as the land, the study said.

Island species, such as those of the Hawaiian Islands, which live on land, are much more affected than continental species. 

The authors noted in the study that the rate of extinction of plants seems lower than that of terrestrial animals.

The study points out that some people deny the fact that the Sixth Extinction has begun. Also, some people believe that the declining abundances of organisms is a new and natural evolutionary trajectory, because humans are just another species playing their natural role in Earth's history. 

The study said that some people even consider that biodiversity should be manipulated solely for the benefit of humanity.

Humans Are The Only Species Manipulating The Biosphere

Cowie said that humans are the only species capable of manipulating the biosphere on a large scale. He asserted that humans are the only species with a conscious choice regarding the future of Earth's biodiversity.

Various conservation initiatives to fight the crisis have been successful for certain charismatic animals. For instance, India will be reintroducing the Cheetah, which went extinct in the 1960s in the country. 

However, the initiatives cannot target all species, and cannot reverse the overall trend of species extinction.

Cowie said it is clear that political will is lacking, despite the rhetoric about the gravity of the crisis. 

He explained that denying the crisis, accepting it without reacting, or even encouraging it constitutes an abrogation of humanity's common responsibility. These factors pave the way for Earth to continue on its sad trajectory towards a Sixth Mass Extinction, he concluded.