Biodiversity crisis in the geological past: The Great Dying

The Permian-Triassic mass extinction was the largest biodiversity crisis ever, called the Great Dying. Almost 90% of all life died while the environment underwent a dramatic transformation. In this article we look at causes and compare it with the biodiversity crisis we face today. We also do a little experiment: putting humans in the Permian world. Was it like on Frank Herbert's Arrakis? 

The Great Dying refers to the biodiversity crisis at the end of the Permian (the geological period between ~300 and ~250 million years ago). 90% of all life in the sea died, and 75% of life on land. Many insects perished, including the largest that ever existed, known as Meganeura. The world changed so dramatically that geologists there drew the line between the Paleozoic with its 'old' life (time of abundant marine life, trilobites, first vertebrates, fish, first terrestrial life, etc.) and the Mesozoic (time of dinosaurs, first mammals, etc.) eras. The greatest changes were seen in the marine fauna. On the land, Glossopteris (a seed fern), was widespread during the Permian but became extinct at the end of that period (this plant was pivotal for nineteenth century scientists to hypothesize continental drift)

There is still debate about the causes of the extreme climate crisis at the end of the Permian, but the most widely accepted hypothesis is that of massive volcanic eruptions in Siberia, on a scale that humanity has not yet witnessed.

Reset button of life

The Siberian Trapps are extensive basalt deposits, formed by a massive outpouring of lava during an event known as a large igneous province (LIP). The lava covered almost half of Siberia. The many lava flows consolidated in horizontal deposits forming staircase-like basalt traps. It was one of the largest volcanic events that ever happened. The emissions of greenhouse gases and aerosols during such a LIP is tremendously high and has far-reaching effects on the climate, environment, and life. In comparison, Tonga, the volcano that recently erupted, spewed much aerosols but in the end had only a minimal effect on climate.

What were the effects of the Permian LIP? The air, oceans and surface waters acidified and caused marine life to die (especially the organisms with a calcite skeleton), as the change is so quick that evolution and adaptation could not keep up. The skies darkened due to the aerosols and smoke, so photosynthesizing organisms also perished. While these environmental changes affected microorganisms and primary producers in the first place, the consequences repercussed into the whole food web, which collapsed like a house of cards. And that is exactly what happened. Life's reset button was pressed. (Stephen Jay Gould used that metaphor quite often in his book Wonderful Life, a great read)

No survival of the fittest

Only few hardy species survived in the most protected ecological niches, and from that impoverished pool, all life that developed later, descends.

Many people still believe that survival of the fittest is the main or only rule that commands evolution and survival, but Stephen Jay Gould suggested other ways of viewing life. Species survive due to contingency. Those who survive were just lucky enough to have a few random traits (maybe not even useful at times when life was good) that help them survive unexpected disasters. But there is no merit in that, and no way to prepare for it, or to evolve towards. 

But why is pondering on evolution relevant when we think of the Great Dying? Humans think they're the dominant species on Earth, but there's no way of predicting that we have what it takes to survive our own climate crisis. The only thing we can do, that other species can't, is learn from past mistakes and act. 

Inhospitable planet

Even before the Siberian Trapps, life during Permian times was already extremely harsh. Due to plate tectonics, all continents had united into one big supercontinent: Pangaea, surrounded by one vast ocean, Panthalassa. There were fewer islands or shallow sunlit seas. Therefore, marine life was suffering as there was less heterogeneity in marine habitats. Furthermore, the land had an inhospitable arid continental climate. It was dry and hot, with large temperature extremes, and at times it may have been about 60 degrees Celsius, maybe not unlike the Sinai desert today (picture in the title).

Besides from the volcanism, there may have been other (partial) causes of the Great Dying, like a depleted ozone layer. Maybe there had been a supernova or gamma ray burst, and/or excessive emissions of hydrogen sulphide, formed by bacteria. All are detrimental to ozone. With less ozone, more UV-radiation reaches the earth's surface and damages life.

In short, our planet was particularly inhospitable by the end of the Permian already before the Siberian LIP volcanoes started to erupt.

Methane emissions from China

Not only carbon dioxide but also methane emissions are to blame, has recently been hypothesized. A team of British and Chinese scientists found that an enormous amount of methane had escaped from another large igneous province at the end of the Permian: the Emeishan Trapps (in Sichuan, China). When it erupted, a staggering amount of 1440 gigaton of methane had leaked into the atmosphere. This amount corresponds to a thousand times the carbon dioxide emitted by humanity so far.

But why so much methane? Heat rising from the Earth's mantle underneath the volcanic area warmed ancient carbon and oil deposits, which released methane. Being volatile, methane worked its way through fissures and cracks and entered the atmosphere.

Methane from landfills

Methane is the simplest organic substance, consisting of one carbon atom surrounded by four hydrogen atoms. It originates mostly from biological processes: as a decomposition product of dead life, through the gastrointestinal system of ruminants, through peat soils, and through gas hydrates on the sea floor, and in permafrost (that's why we don't want permafrost to melt). 

Methane plumes on other planets or moons could be a sign of microbial activity, and are the subject of very active areas of research (even through non-biological sources must not be ruled out).

A human source of methane are large landfills. In the absence of oxygen, organic waste at the bottom of the landfill produces methane. Methane plumes from landfills are detected on satellite images.

Methane contributes to climate change and it is advisable, to say the least, that methane production be addressed if we are to turn the tide for the current biodiversity crisis - actually the sixth extinction wave. 

Like Arrakis?

Extinction waves in the geologic past happened a couple of times, some worse than others, but always at a relatively slow rate (except for the meteorite impact at the end of the Cretaceous). In Permian times, it took thousands or even a million years before all the dying had happened, and for life to start, slowly, with a new slate. And although many lifeforms suffered greatly during these harsh times, the downfall itself would have been barely noticeable within a human lifetime. 

And what if humans lived during the Permian? They would have found our planet extremely cruel and hostile. The planet would not have been able to sustain a large population of humans. I like to think that the Earth then was like Arrakis in Herbert Frank's book Dune, where water was extremely scarce, and the environment almost uninhabitable.

Where humanity is today, with all its prosperity, is only possible because the climate has been very mild and pleasant for the last ten thousand years, allowing the flourishing of a lush, generous nature. And yet a staggering million species are threatened with extinction, according to the latest IPBES Global Assessment report, and the number is rising.

LIP in the future?

The analogy between the late Permian world and the current climate crisis is crystal clear: greenhouse gases lead to climate change with dire consequences for biodiversity and life in general.

It is also useful to contemplate the consequences of a large igneous province (LIP). The current anthropogenic climate crisis may turn out being an exercise in facing a LIP sometime in the future. Such an event occurs every few tens of millions of years. Humanity has yet to witness a LIP, but one day, we will. Are we prepared for it? Great sums of money, as those spent by NASA, should rightfully be invested in volcanic risk assessment, eruption aftermath recovery and climate crisis preparedness and mitigation. 

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Read more: Large volcanic eruptions can have a cooling effect on climate, as was expected from Tonga, though for now-understood chemical reasons it did not cause cooling. Prolonged episodes of drought contribute to desertification and soil erosion, which in the 30s lead to the Dust Bowl disaster. Such calamities may affect semiarid regions like Spain. Much dry vegetation increases the risk of wildfires setting large swaths of land ablaze, leading fire experts such as Stephen Pyne to define our current era as the Pyrocene. A crisis also struck the Mediterranean, which dried out almost completely about 5 million years ago, even though it was caused by the action of plate tectonics and not climate. To understand and quantify how and whether humanity can live and thrive on Earth, scientists have defined nine planetary boundaries, which are values related to certain earth-system properties that are better not exceeded. As to quantify the human-induced effect, I calculated how much faster anthropogenic climate change progresses as opposed to natural global warming. 

Sources: 

Phys.org News, 2022, Lancaster University, Methane discovery sheds new light on world's largest mass extinction event. 

Article written by Kathelijne Bonne, geologist and soil scientist. I also write on Good Climate News. 

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