19-September-2023-Special-Article

SIXTH MASS EXTINCTION MORE SEVERE THAN ESTIMATED, 73 GENERA VANISHED SINCE 1500: STUDY

Article Source: Down to Earth

Let’s first understand what a mass extinction is?

First, we need to be clear on what we mean by ‘mass extinction’. Extinctions are a normal part of evolution: they occur naturally and periodically over time.

There’s a natural background rate to the timing and frequency of extinctions:

10% of species are lost every million years; 30% every 10 million years; and 65% every 100 million years.

It would be wrong to assume that species going extinct is out of line with what we would expect. Evolution occurs through the balance of extinction – the end of species – and speciation – the creation of new ones.

Extinctions occur periodically at what we would call the ‘background rate’. We can therefore identify periods of history when extinctions were happening much faster than this background rate – this would tell us that there was an additional environmental or ecological pressure creating more extinctions than we would expect.

But mass extinctions are defined as periods with much higher extinction rates than normal. They are defined by both magnitude and rate.

Magnitude is the percentage of species that are lost.

Rate is how quickly this happens. These metrics are inevitably linked, but we need both to qualify as a mass extinction.

In a mass extinction at least 75% of species go extinct within a relatively (by geological standard) short period of time. Typically, less than two million years.

Extinction Event	Age(mya)	Percentage of species lost	Cause of extinctions
End Ordovician	444	86%	Intense glacial and interglacial periods created large swings in sea levels and moved shorelines dramatically. Tectonic uplift of the Appalachian mountains created lots of weathering, sequestration of CO2 and with it, changes in climate and ocean chemistry.
Late Devonian	360	75%	Rapid growth and diversification of land plants generated rapid and severe global cooling.
End Permian	250	96%	Intense volcanic activity in Siberia. This caused global warming. Elevated CO2 and sulphur (H2S) levels from volcanoes caused ocean acidification, acid rain, and other changes in ocean and land chemistry.
End Triassic	200	80%	Underwater volcanic activity in the Central Atlantic Magmatic Province (CAMP) caused global warming and a dramatic change in the chemical composition in the oceans.
End Cretaceous	65	76%	Asteroid impact in Yucatán, Mexico. This caused a global cataclysm and rapid cooling. Some changes may have already pre-dated this asteroid, with intense volcanic activity and tectonic uplift.

The Sixth Mass Extinction

Human actions are compounding the severity of the ongoing sixth mass extinction, according to a new study.

The current rate at which the entire genus of vertebrates, or animals with spinal cords, are going extinct is 35 times greater than the last million years.

What is a Genus?

A genus is a group of animals or plants which share some common characteristics. For example, dogs and wolves are in the same genus, Canis.

Between 1500 and 2022 AD, 73 genera (plural of genus) of vertebrates (excluding fish) went extinct, the study published.

Humans putting a dent in the evolution of life

Humans are putting a big dent in the evolution of life on the planet in the long term, Gerardo Ceballos, senior researcher at the Institute of Ecology at the National Autonomous University of Mexico and one of the authors of the paper, said in a statement.

“But also, in this century, what we’re doing to the Tree of Life will cause a lot of suffering for humanity,” Ceballos added.

Previous studies have focused on the extinction of species and found thousands of species and myriad populations have vanished.

For example, around 10,000,000 African elephants roamed Earth at the beginning of the 20th century. Now, only about 450,000 remain.

The Research Findings

The team first gathered information on species’ conservation statuses from the International Union for the Conservation of Nature, Birdlife International and other databases. Overall, they examined 5,400 genera of land-dwelling vertebrate animals.

Their analysis showed that 73 genera of land-dwelling vertebrates have vanished since 1500 AD.

The biggest victims

Birds, they found, suffered the heaviest losses with 44 genus extinctions, followed by mammals (21 genus extinctions), amphibians (five extinctions) and reptiles (three extinctions).

Humans have fuelled a surge of genus extinctions in the last five decades, which otherwise would have taken 18,000 years to occur.

The Pace of Extinction is alarming

Most extinctions were recent. The years between 1800 and 2022 saw 55 total extinctions. Birds ranked the highest with 36 extinctions, followed by mammals (12), amphibians (five) and reptiles (two).

Without humans, the researchers estimated that Earth would likely have lost only two genera between 1500-2022.

“This mass extinction is transforming the whole biosphere, possibly into a state in which it may be impossible for our current civilisation to persist,” the researchers wrote in their paper.

What does it mean to lose a genus?

Losing a genus could impact the functioning of an entire ecosystem.

For example, when the passenger pigeons went extinct, it narrowed human diets in north-eastern North America and altered ecosystem structure over wide areas.

It also triggered population declines of cougars and wolves, leading to shifts in rodent communities.

The region, according to the paper, became more conducive to outbreaks of infectious diseases that jump from animals to humans. An example is Lyme disease, a bacterial infection spread to humans by infected ticks.

Then, there is also climate change.

“Climate disruption is accelerating extinction and extinction is interacting with the climate because the nature of the plants, animals, and microbes on the planet is one of the big determinants of what kind of climate we have,”.

Important for Prelims

International Union for the Conservation of Nature

Birdlife International

Timeline of Extinctions

Sixth Mass Extinction

Mains Questions

1. Define Mass Extinction. Discuss the role of humans in increasing the pace of extinction. (150 Words) 10 Marks
2. Though, humans are blamed for the mass extinction, climate change also has a role to play. Comment (150 Words) 10 Marks