Exploring the Environmental Ruin of the Permian Mass Extinction

252 million years ago, life on Earth almost ceased to exist as a volcanic apocalypse heralded the Permian Mass Extinction.

When it comes to mass extinctions, the demise of the non-avian dinosaurs gets most of the attention. However, while the Cretaceous-Palaeogene extinction event of 66 million years ago was indeed one of the most devastating in Earth’s history, there was a time much further back when life on our green planet almost vanished in its entirety. Known as the Great Dying, the Permian Mass Extinction heralded the end of the Palaeozoic era and saw some 90% of all species on Earth disappear forever, leaving an environmental catastrophe in its wake.

Thanks to recent advances in radiometric dating, we now know when the Great Dying occurred to within a thousand years of accuracy, which is quite extraordinary given that it happened a shade under 252 million years ago. Even more disturbingly, the event spanned as little as 50 thousand years, which is a mere drop in the bucket when it comes to geological timespans. During this relatively short time, the Earth’s environment saw unprecedented change, brought about by a combination of factors that we’ll be exploring in this article.

What Was Life Like Back in the Late Permian?

Dmitry Bogdanov

Dimetrodons were among the largest land-dwelling animals of the Permian Period.

Long before the dinosaurs roamed the Earth, the Permian Period saw the rise of amphibious megafauna and synapsids, the ancestors of all modern mammals. It was a world of lush primeval jungles in which plants spanned every landmass on Earth. While climates changed throughout the period, beginning with an ice age that had come about during the end of the preceding Carboniferous, things started looking bad between 262 and 259 million years ago, when extreme volcanism obliterated large swathes of what is now modern China.

The last epoch of the Permian, known as the Lopingian, saw a world reshaped by volcanism, but one in which biodiversity had managed to remain at a healthy high. We can discern this by studying the Emeishan Traps, a region of volcanic flood basalts in China. The immense volcanic uplift at the time brought about the End-Capitanian extinction event which, despite not being labelled among the traditional ‘Big Five’, was significantly more severe than the one that killed off the dinosaurs. This event set the precedent for what was to come, with the transformation of Earth’s climate now well underway.

The rich biodiversity that saw great beasts like dimetrodons and dinocephalians rise to dominance was under great threat during the Late Permian. The world was getting warmer and drier. At the same time, most of the continents were joined together in the form of the prehistoric supercontinent of Pangaea, which left relatively little room for biodiversity. Instead, as evolution has always done, species struggled for dominance in an increasingly harsh world, but far worse was yet to come.

Rising Greenhouse Gasses Devastate Earth’s Ecosystems

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Today, modern industry has a major impact on increasing CO2 levels.

In an alarming correlation between modern climate change and the most severe extinction event of all time, scientists have determined that rising CO2 levels and, later on, methane, were largely to blame for laying waste to marine ecosystems 252 million years ago. Many marine animals rely heavily on stable CO2 levels, since CO2 is absorbed by seawater to create calcium carbonite, which is a crucial building block for numerous marine organisms, such as molluscs and arthropods. However, should CO2 levels increase too much and too quickly, seawater becomes too acidic for most of these organisms to survive.

Back in the end of the Permian Period, rising CO2 levels were quick to wipe out a staggering 96% of all marine species, as well as countless more terrestrial species that relied on sea life for sustenance. Among the victims were the trilobites and eurypterids, which had dominated the seas for well over 200 million years, which is far longer than even the non-avian dinosaurs. Picture the scenario for a moment – in just a few thousand years, hundreds of millions of years of evolution had been largely undone, and this was ultimately due to an unprecedented increase in CO2.

As the events of the Late Permian so perfectly demonstrate, the stability of CO2 in the atmosphere is crucial for maintaining biodiversity. Too much, and the sea becomes too acidic and a runaway greenhouse effect leaves the land dry, hot and barren. Too little, and the world would cool too much, and photosynthesis would fail catastrophically. With rapidly rising CO2 levels, possibly reaching a peak of around 1,800 parts per million according to the GEOCARB III survey, terrestrial ecosystems were also in trouble. Without having enough time to adapt to rapidly drying and warming climates, and with global surface temperatures heating up as much as 11°C, around 70% of terrestrial vertebrates also disappeared.

The Great Dying also has the distinction of being the only mass extinction of insects in Earth’s history. Like the Carboniferous before it, the Permian was known for its enormous insects, which were partly a product of the much higher percentage of oxygen in the atmosphere at the time. While insects had long been decreasing in size as they adapted to lowering oxygen levels since the Carboniferous Rainforest Collapse of 305 million years ago, the Late Permian saw nearly a dozen insectoid orders disappear for good. This was likely down to a combination of factors, including a change in plant diversity and oxygen levels which continued to drop with the decline of photosynthesising plant life and increased volcanic activity.

Identifying the Bringer of Death

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Throughout Earth’s history, volcanism has played a major role in reshaping environmental conditions.

Even though we know that rising greenhouse gas levels and climate change were ultimately responsible for the Great Dying, pinning down the underlying cause is extremely difficult. After all, the event happened an unimaginably long time ago, and a great deal has happened since then, including the rise and fall of the dinosaurs and the rise of mammals after that.

Not much remains of the Permian Period, given that it ended, along with the Palaeozoic Era, 252 million years ago. As such, the story of the Great Dying is one that will forever be incomplete. Rocks from this far-off time are relatively scarce, and given that the sea floor is completely resurfaced by tectonic activity every 200 million years, even the most inaccessible depths of the Earth’s oceans hold no clue.

It’s not even known for certain whether the Great Dying was a sudden, catastrophic process or a much more gradual one. While there’s no doubt that the event was relatively short in geological terms, the gradual hypothesis points to the event lasting around 5 million years, during which gradual climate change and increased oceanic acidity, likely brought about by increased volcanic activity, stifled evolutionary progress. Nonetheless, the peak of the extinction event appears to have lasted in the tens of thousands, rather than millions, of years.

Although impact events, such as the Chicxulub impactor that heralded the eventual fall of the dinosaurs, have been considered, volcanism is by far the most likely main culprit behind the environmental catastrophe. Volcanic activity has long had a major impact on the planet’s environment. It is, after all, by far the largest natural producer of CO2.

A major increase in volcanism has the inevitable effect of warming the climate with greenhouse gasses which, in turn cause sea levels to rise and permafrost to melt. When permafrost melts, trapped methane gets released, further warming the environment. Volcanism also causes acid rain which devastates ecosystems as we’re seeing now in the case of man-made environmental pollution. Ultimately, what we have is a result is a sort of catastrophic domino effect that leaves behind an arid desert world, a highly acidic and anoxic ocean and a severely damaged ozone layer.

Life in a Desert World

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After the Great Dying, most of the planet’s landmasses were dominated by vast swathes of desert.

The world was not a pleasant place during the Permian-Triassic boundary. If you’ve ever read Frank Herbert’s classic novel Dune, you could perhaps compare the environment to that of the fictitious desert planet of Arrakis (albeit without the giant sand worms!). The environmental apocalypse had left behind a largely dry and barren landscape dominated by vast deserts that were, for the most part, lifeless. The average global surface temperature reached 29°C, which is almost twice as high as it is today.

Perhaps counterintuitively, sea levels had also reached their lowest ever point by the end of the Permian, being some 66 feet (20 metres) lower than they are today. Given that the period of glaciation of the Early Permian had already been over for many millions of years, one might assume that sea levels should have been much higher. After all, the poles were free of ice, and it’s likely that the only ice would have been restricted to very mountainous regions. The greatly reduced sea level was likely a result of the fact that the then supercontinent of Pangea had reached its maximum packing capacity, increasing the size of the ocean basin and therefore increasing the size of the ocean while also lowering sea levels in relation to the Pangean shorelines.

Only the hardiest of species made it through the Great Dying. While localized biodiversity had been devastated across the planet, the land and sea were not completely dead. Therapsid megafauna, the direct ancestors to modern mammals, survived, with hardy creatures like dicynodonts clinging on in the arid environment. A handful of brachiopods (shelled marine creatures similar to molluscs) also survived, although some 96% of their relatives did not. Similarly, around 4% of anthozoan species (anemones and stony and soft corals) survived. In the sea, bivalves and ostracods survived in relatively large numbers, and continue to form an important and extremely long-lasting component of maritime ecosystems to this day.

As one might expect, the world after the Great Dying certainly wasn’t a green one. The dense forests that had colonised almost every area of the planet during the Early Permian had all but vanished, and floral taxons changed profoundly. In fact, plant life had taken such an enormous hit, unlike ever before, that there’s also a vast coal gap spanning the entirety of the Early Triassic. There are no coal deposits known from this period, since there was minimal plant life left to decay and replenish the coal deposits formed previously.

Once the Great Dying had heralded the end of the 289-million-year-long Palaeozoic Era, it would take 30 million years for biodiversity to recover. However, this period also set the stage for the rise of the dinosaurs, which would dominate Earth’s terrestrial ecosystems right up until 66 million years ago.

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Let’s conclude our story on a more positive note – every mass extinction presents a new opportunity for previously underrepresented species to dominate and evolve down a different path. Nonetheless, there’s a lot that we and our own dominance over the world’s ecosystems can learn from our planet’s worst mass extinction, despite the fact it happened so long ago. We’re currently living in the sixth major mass extinction of all time but, this time, we’re at least partly to blame.

Further Reading