Context: According to a new research published in the journal Proceedings of the National Academy of Sciences of the United States of America (PNAS), the ongoing sixth mass extinction may be one of the most serious environmental threats to the persistence of civilisation.
Key Findings of the study

• The study analysed 29,400 species of terrestrial vertebrates and determined which of these are on the brink of extinction because they have fewer than 1,000 individuals.
• The disappearance of their component populations has been occurring since the 1800s.
• Most of these 515 species are from South America (30 per cent), followed by Oceania (21 per cent), Asia (21 per cent) and Africa (16 per cent) among others.
• The research claims that this extinction is human-caused and is more immediate than climate destruction. 
• Even though only an estimated 2% of all of the species that ever lived are alive today, the absolute number of species is greater now than ever before. 
• It was into such a biologically diverse world that we humans evolved, and such a world that we are destroying.

What is Mass Extinction?

• The fossil records show that something unusual happened millions of years ago. A wide range of animals from terrestrial megafauna to tiny aquatic beings died suddenly. This extinction of a large number of animals altogether is known as a mass extinction.
• As the new species start evolving, the old species get depleted from the earth. More than 90% of the species are believed to have become extinct in the last 500 million years.
• Mass extinctions are deadly events. The Permian Triassic extinction took place 250 million years ago. It gave rise to the era of dinosaurs. 96% of the marine species were depleted during the “Great Dying”. The fossils from the ancient sea floor depict the diversity of life at sea.

About Six Mass Extinctions
1) Ordovician-Silurian Extinction

• During this extinction, the life of small aquatic organisms ended. This happened 440 million years ago. 60% of the animal species got extinct during this period.

 Causes

• Beginning of glacial cycles on Earth, and corresponding changes in sea level
• Changes in atmospheric and oceanic chemistry relating to the rise of the Appalachian mountains

2) Devonian Extinction

• It marks the extinction of tropical marine life forms. It occurred 20 million years ago. 70% of the marine species including the coral reefs became extinct in the shallow areas of the sea.

Causes

• Climate change, possibly linked to the diversification of land plants
• Decrease in oxygen levels in the deep ocean

3) Permian-Triassic Extinction

• It is the largest mass-extinction known which depleted a wide range of species, including vertebrates. This was an abrupt extinction. 96% of the marine and terrestrial animal species became extinct and therefore the event is known as the “Great Dying”.
• It is thought to be the result of a massive volcanic activity or a comet striking the surface of the earth.

Causes

• Volcanic activity
• Climate change
• Decrease in oxygen levels in the deep ocean
• Changes in atmospheric chemistry
• Changes oceanic chemistry and circulation

4) Triassic-Jurassic Extinction

• This took place 18 million years ago at the end of the Triassic age. All the terrestrial and marine reptiles and plants species including the dinosaurs were wiped out.

Cause

• Volcanic activity

5) Cretaceous-Tertiary Extinction

• This marks the extinction of nonavian dinosaurs. They were wiped out at the end of the Cretaceous period and the beginning of the Tertiary period. Hence called KT extinction.
• This marked the dawn of a new age. This extinction took place 65 million years ago when a massive asteroid hit the earth’s surface.
• This led to immense changes in the atmosphere, sea levels and temperatures that ended the life on earth.

Causes

• Asteroid impact
• Volcanic activity
• Climate change
• Changes in atmospheric and oceanic chemistry

6) Sixth Mass Extinction

• We are currently in the middle of the sixth mass extinction, and humans are the major cause of it. The humans have killed most of the animal species for their own benefits.
• The invasive species were transported from one part of the world to the other which eliminated the native species. Also, the immigration and emigration of humans and animals have spread certain diseases in different parts of the world where they were never present before.
• The chemicals have harmed marine life. The natural resources are depleting due to the growing population. Heavy pollution has led to an increase in temperatures and water levels in the sea which will have catastrophic effects on the life on earth in the near future.

Impact of species extinction

• Loss in crop pollination: According to the Center for Biological Diversity, when species go extinct, the impact can be tangible such as in the form of a loss in crop pollination and water purification. 
• Impacting food chain: 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.
• For instance, when the wolves in Yellowstone Park in California, US, were hunted to near extinction by the 1930s, the deer and elk they preyed upon thrived, as a result of which their grazing decimated the streamside willows and aspens, which provided habitat for songbirds.
• Contribution to ecosystem functions may be lost: When the number of individuals in a population or species drops too low, its contributions to ecosystem functions and services become unimportant, its genetic variability and resilience is reduced, and its contribution to human welfare may be lost.

Suggestions

• Significantly, the study calls for a complete ban on wildlife trade as many of the species currently endangered or on the brink of extinction are being decimated by legal and illegal wildlife trade.
• Researchers point out that the current COVID-19 pandemic, while not fully understood, is also linked to the wildlife trade. 
• There is no doubt, for example, that there will be more pandemics if we continue destroying habitats and trading wildlife for human consumption as food and traditional medicines.