It is hard to believe that since life began nearly 3.8 billion years ago, 99 percent of all living things that have ever lived on Earth have become extinct. What we see today is just a minuscule 1 per cent of all life that has ever lived on Earth. In fact, it is almost a miracle that life continues to exist at all!” elucidates author Pranay Lal in his enthralling book ‘Indica – A Deep Natural History of The Indian Subcontinent’.

The Cretaceous-Tertiary Extinction or the K-T Extinction event - that claimed, along with other 80 percent of the then existing species, the dinosaurs.

Photo: PxHere

It is sobering and exciting in equal measure to truly grasp the gravity of this piece of knowledge. The mind-bending array of present day diversity (from the modern day single-celled bacteria to towering giraffes) that surrounds us leads us to deceptively assume that it is easier for life to exist than not, on this planet, when the truth is diametrically opposite to this juvenile worldview.

Life Barely Survived The Mass Extinctions

Earth’s long geological history has been dramatic and a violent one, marked with cataclysmic events of all scales. Life on the planet has been prodded and shaped by five major mass extinction events over the last 500 million years which have been responsible for erasure of 70 percent to 96 percent of species each time, and each time the surviving species have had to recover, reassemble and start from the beginning. Each time the trajectory of evolution has had to reconfigure under newer conditions to make way for newer species to form and diversify. But each time, an equilibrium on the planet was achieved.

Speaking of mass extinctions, the most famous one undoubtedly comes to mind – the Cretaceous-Tertiary Extinction or the K-T Extinction event – that claimed, along with other 80 percent of the then existing species, the dinosaurs. A meteor 5-15 km. in diameter, named Chicxulub, hurtled towards the Earth at a deathly speed, 65-66 million years ago, and crashed into the Gulf of Mexico, close to where Yucatan Peninsula sits today. This collision may have raised unimaginable amounts of dust, gas and debris filling the skies, shrouding a large part of the planet into darkness. The massive meteorite collision in addition to the continued Deccan volcanic eruptions in the Indian subcontinent that caused the biggest lava floods in Earth’s history could have proved to be too much for life on land and in water. The resulting mega-tsunamis, fiery heat, spewing of billions of tonnes of sulphur dioxide and other toxic gases into the atmosphere, changing climate, perhaps, sealed the fate of most species, including the magnificent dinosaurs, eliminating three-quarters of life overnight, in geological terms.

But, it was the the Permian-Triassic extinction event that occurred 252 million years ago which truly tested life’s limits of resilience and remains unparalleled in the extent of devastation it caused, nearly ending all life on the planet. Fittingly also christened as ‘The Great Dying’, this mass extinction event wiped out nearly 96 percent of all marine species and two-thirds of terrestrial lifeforms on Earth. Scientists have posited quite a few hypotheses debating the real cause of ‘the Great Dying’ over the years, one of the latest ones being global warming most likely triggered by violent volcanic activity that released large amounts of greenhouse gas emissions over the course of hundreds of years. In geological timeframe, this counts as instantaneous. Earth’s temperatures spiked by 10 degree Celsius, it is believed, causing oceans to warm, oxygen levels in the seas to drastically decline, drastic weather events to occur and ecosystems to collapse.

The Big Five Mass Extinctions: Extinction is a normal part of the evolutionary process and most species that have ever existed are not living today. The normal loss of species through time is generally balanced by the rise of new species. Mass extinctions, however, disrupt this balance–representing times when many more species go extinct than are replaced by new ones. Scientists have found evidence of five mass extinction events during Earth’s history.

Click here to view the interactive poster. Credit: HHMI Biointeractive

Today, just a little more than one degree Celsius rise in global temperatures above pre-industrial levels due to man-made emissions of carbon and other greenhouse gas, and we are already witnessing a massive surge in natural catastrophes, unpredictable weather, rise in sea-levels, ocean acidification, and whatnot.

Through the crags and crevices of slim survival opportunities, a minuscule percentage of survivors made it through these mass extinctions, and recovered against all odds. Even the most successful group of animals to have ever lived (not humans!) – the trilobites – perished in the Great Dying after having lived in the seas for nearly 300 million years!

Background Extinction Vs. The Sixth Mass Extinction

The fossil record shows that more than 99 percent of all species to have graced the Earth have become extinct. While a majority of them fell victims to mass extinction events, other species have been lost over time, at rates much slower than those eradicated en masse. Species extinction is a very normal and continuous process, taking place in the background against the usual environmental pressures, local natural disasters, and competition among species for resources. This is called ‘background extinction’. The baseline extinction rate (or the natural background rate), as assumed by the available fossil record, is extinction of one species per million species each year.

But, the present circumstances plaguing the biodiversity on the planet has ushered in, according to the experts, the sixth mass extinction. As per scientific criteria, to qualify as a mass extinction, the planet must register a loss of more than 70-75 percent of all existing species in a short span of time, geologically speaking. Considering the extraordinary length of time that has elapsed since Earth formed (4.5 billion years!), anything up to 2.8 million years constitutes as “short” period of time.

This human-dominated era on the planet is undoubtedly witnessing an extinction crisis. Today, extinction rate is 1,000 to 10,000 times higher than the aforementioned baseline rate. It is estimated that more than 10,000 species are going extinct every year. The cause of this ongoing anthropocene extinction crisis is not hard to determine unlike for the previous ‘Big Five’. It is clear that humans are directly and indirectly responsible for causing it. Habitat destruction; overexploitation of natural resources such as overfishing, hunting, excessive extraction of groundwater, etc.; pollution of all kinds – air, water, sound, and light, carbon emissions, ensuing global warming and a changing climate, among myriad other problems, have resulted in massive loss of biodiversity in a very short span of time. How many species will the man-made sixth mass extinction claim? Will it upstage even the Great Dying?

The dazzling diversity of millions of living species that we see today, old and young, including Homo sapiens, makes up a mere one percent that has managed to evade extinction so far. Care to venture a guess about the total number of species to have ever made an appearance on Earth? We haven’t been able to accurately surmise the number of existing species on the planet even! The rough figure hovers around 9 million. As to the question of how many species that ever lived on the planet, I know for sure, that it is a number beyond comprehension.

Every species has to, at some point, go extinct. Having said that, this fact does not condone or justify humans’ reckless and highly destructive behaviour that has triggered the current deadly upsurge of species extinction on the planet.

Paradoxically, extinction is life’s one true constant. And, extinction is forever.

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About the author: Purva Variyar is a conservationist, science communicator and conservation writer. She works with the Wildlife Conservation Trust and has previously worked with Sanctuary Nature Foundation and The Gerry Martin Project.

Disclaimer: The author is associated with Wildlife Conservation Trust. The views and opinions expressed in the article are her own and do not necessarily reflect the views and opinions of Wildlife Conservation Trust.

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