At some point in history, almost all species on land and sea disappeared. We now know why. The Permian mass extinction, informally referred to as the Great Dying, is considered one of the largest geological events in the history of life on Earth. In a relatively short period of time, about 70% of vertebrates living on land and about 90% of marine species disappeared from the face of the earth. The massive Permian extinction, to be honest, just became the largest earthly disaster. After all, the Earth for us is, first of all, life.
Ten years ago, it was not known for certain which trigger pulled this very deadly disaster 252 million years ago. The reason was shrouded in mystery, scientists proposed dozens of theories.
And so, more recently, advances in dating technology and the search for geological evidence have provided a precise indication. Most scientists on Earth agree that the greatest of the Big Five extinctions was caused by a million years of volcanic activity.
But has this riddle been solved? Not really.
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Yes, somewhere around 5 million cubic kilometers of lava came out somewhere in today's northwestern Siberia - enough to cover the Earth's surface 10 meters deep - and this happened just before the mass extinction began. This triggered the release of huge volumes of greenhouse gases that have underpinned global warming and severely disrupted the Earth's life support systems.
Nevertheless, the exact details of how exactly this led to the extinction of so many life forms remain the subject of fierce scientific debate.
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And this is not just academic interest. This catastrophic event played an important role in shaping the flora and fauna that we see today. In addition, there are clear parallels between the environmental changes that took place then and are observed today. Some say that raising our species' awareness of the times when life almost ceased to exist will help us ensure our own long-term survival.
In 1980, Louis and Walter Alvarez, a father and son at the University of California, Berkeley, provided new and compelling evidence that the most famous of the mass extinctions - the one that occurred 66 million years ago - was the result of a massive asteroid falling. And they sparked a wave of interest in the causes of other mass extinctions, including the largest of the late Permian.
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Back then, Western extinction hunters had less evidence to access because they were located in China and Russia, not the most open countries. But this did not stop them from proposing various theories.
Some have pointed to the side effects of the formation of the Pangea supercontinent, such as lowering the depth of the marine habitat, where most marine species lived. Others have pointed to a sharp drop in oxygen in late Permian rock samples and a drop in sea levels - both of which might explain why marine species had such a lousy experience.
Others have suggested a massive release of methane from the seabed. There was also the option that the intense volcanism that left so much volcanic rock in Siberia was a special factor. Each subsequent lava flow spread on the previous one, creating a series of stepped hills. They got the name Siberian traps - from the Swedish "trapp", that is, steps.
“The end of Permian mass extinction was then thought to have stretched out over several million years,” says Paul Vignal, a geologist at the University of Leeds who published The Worst of Times in September 2015 on mass extinctions.
After collecting samples in the Dolomites, Italy, Vignal and Anthony Hallam of the University of Birmingham concluded in an article published in 1992 that the extinction actually lasted tens or thousands of years.
This short time frame has prompted many to go in search of a short but acute catastrophe that could explain the extinction - for example, the fall of an asteroid.
In favor of this idea, some scientists point to rare grains of shock quartz in Australia - grains of sand that were at the site of the alleged impact and were subjected to strong physical impact in this process. Other scientists working in Antarctica have discovered helium and argon with an isotopic ratio similar to that of carbon-rich meteorites in the early solar system.
But no impact crater was found, and everything died out.
“We simply do not have geological evidence of an impact or any other major event that could lead to an extinction of this magnitude, other than the Siberian traps,” says Jonathan Payne, a geologist and mass extinction specialist at Stanford University in California, USA.
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As dating methods improved and samples were collected, volcanism gradually became the main culprit - in particular, after scientists concluded that Siberian traps formed about a million years ago, and not 10-50 million years, as previously thought.
The consequences of the Siberian traps were dire. The largest impacts were observed in the oceans, in particular on the seabed.
Many groups have disappeared completely, including one of the earliest groups of arthropods - trilobites - and primitive rugoses, corals, blastoids, relatives of modern sea urchins and sea stars. Others, like brachiopods, bryozoans, squid-like ammonites and sea lilies, have lost most of their species.
The swimmers were a little more fortunate: acanthodes and placoderms became extinct, but many other fish and eel-like conodonts remained practically intact.
Terrestrial organisms were also affected. Many major groups were destroyed, including the gorgonops, the saber-toothed dominant predators of the time, and the bulky herbivorous pareiasaurs.
According to Dmitry Shcherbakov of the Paleontological Institute in Moscow, about 40% of insect families from the end of Permian were destroyed. Many equatorial groups, such as cockroaches and cicadas, moved north as temperatures rose.
In terms of plants, forest species have practically disappeared.
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Many groups of dominant gymnosperms have declined. Coal has not been produced for about 10 million years, indicating the disappearance of peat-forming plants. Another sign of unambiguous lethal destruction of plants is the "mushroom leap" - a huge increase in the number of fossilized fungal spores.
“This is being interpreted as the result of an explosion of mushrooms living on dead or dying trees,” says Barry Lomax of the University of Nottingham in the UK. "We have not seen anything like this on any other geological boundary."
An accurate analysis of what died and when it died thus offers some of the best clues that will explain how Siberian traps could have had such a big impact.
When Vinyal and colleagues at the China University of Terrestrial Sciences in Wuhan examined in detail the samples showing the fate of 537 marine species in China, they found that 92 percent of them had been destroyed. They also found that the extinction took place in two phases, separated by 180,000 years.
The first was especially fatal to shallow-water inhabitants like corals, living on the bottom of microscopic animals fusulinids and plankton of radiolarians. The extinctions of the second wave occurred in the depths of the ocean.
New species developed fairly quickly after the first wave, but recovery was much slower after the second - most likely due to long-term reasons that have eroded the deep foundations of many ecosystems. Other evidence from plant remains recovered in Greenland and Antarctica supports the idea of a double mass extinction.
What was it about Siberian volcanism that caused so much destruction for life in its various Permian manifestations?
Together with the lava, huge volumes of greenhouse and other harmful gases came out. These included huge volumes of carbon dioxide and sulfur dioxide, which led to rising temperatures.
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The heating of the oceans reduced their ability to hold oxygen, and the currents that normally carried oxygen into the depths could slow down or stop. Lack of oxygen is believed to have been the main cause of the marine extinction, as shown by rock samples at the boundary between two geological periods in various locations around the world.
“Nearly all the sediment we looked at went from being rich in oxygen and life to poor in oxygen and life,” says Mike Benton, a paleontologist at the University of Bristol. "This line is as absolute as the edge of a knife and is clearly visible."
Some point out that as the level of carbon dioxide in the atmosphere increased, its level also increased in the oceans, the water became more acidic and less likely to encourage marine organisms to make their shells. The increased level of carbon dioxide in general had a negative effect on the oxygen exchange system of marine animals.
"People talk about the deadly trinity of warming, acidification and deoxygenation," says Payne, who claims acidification could last for tens of thousands of years. "All these things affect the life of marine animals, their metabolism and the use of oxygen."
Vignal, however, plays down the role of ocean acidification. "No doubt if you acidify the ocean's surface it will, but most organisms can still make their shells because they do it in their bodies, without contact with the surrounding seawater."
The warming had significant consequences for the land - but incomparable with those that led to extinctions of such proportions at that time. Geologists blame the release of harmful CFC-like gases like chloromethane.
These gases are thought to be generated when layers of coal and salt heat up as magma moves up to the Siberian surface. They lead to the destruction of the ozone layer, which leads to a significant increase in the exposure to harmful ultraviolet radiation from the sun.
Arguments to support this theory emerged in 2004 when Henk Vischer of the University of Utrecht in the Netherlands presented evidence of a significant increase in fossilized mutated lymphoid spores during the late Permian mass extinction.
Others have suggested that environmental stressors like increased aridity, rather than increased radiation, may have caused mutations. Lomax, however, supports Vischer's theory. "There have been other periods of prolonged dryness, and we see no evidence of any association with spore mutation, so it seems more logical to attribute them to UV radiation."
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The gases escaping from the volcanoes formed carbolic, sulfuric and other acids, which fell in the form of acid rain, exacerbating the environmental hazard. This demonstrates how the environment could destroy species directly and indirectly overnight.
“Plant loss from UV radiation and acid rain should have removed the backbone of the food chain on land, leading to starvation of herbivores, which in turn were the food source for carnivores,” says Benton.
Many believe that these ecosystem relationships should be thought of by the people of the 21st century, as our activity raises the concentration of carbon dioxide in the atmosphere to an extreme level. The extinction of the end of the Permian period provides food for thought.
“In essence, we are creating or accelerating the end-of-Permian mass extinction,” says Vignal. “However, it will take a long time to warm up the oceans, and the models show that the oceans will be in trouble in 200-300 years in terms of dissolved oxygen content, and problems with ocean circulation will appear in a couple of thousand years. Who knows what we will do then."
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Payne points out that the late Permian mass extinction could be seen as beneficial to life in the long term - the total number of species on Earth eventually grew even more than it did - but its timeline provides no food for comfort.
“The biggest extinction in life history has a lot to do with the environmental changes that are happening today and that can be expected in the next 100-1000 years,” he says. "In fact, in the long term, this will have a stimulating effect on the diversity of the ecosystem, but recovery will take millions of years, so the loss of diversity is hardly beneficial for human society."
In his 1993 book The Great Paleozoic Crisis, American paleobiologist Doug Erwin compared the problem of assessing the potential causes of the end-Permian mass extinction with the situation faced by Hercule Poirot in Murder on the Orient Express. Detective Agatha Christie ultimately concludes that all the passengers on the train were involved in the murder.
In his latest book, Vignal describes Poirot's conclusion that "everyone did it" as "lazy." Instead, he cites the example of Sarah Lund, star of the Danish crime drama Murder. The list of suspects grows with each series. (It would be more convenient for us to cite Chekhov's "The Seagull" as an example). Vignal's killer is volcanism, resulting in warming, ocean deoxygenation and ozone depletion.
However, scientists are gaining access to a growing body of increasingly accurate data trying to isolate differences in the exact combinations of causal factors for extinction in different ecosystems, groups and species, which may not provide direct answers. If this is one crime play, then it is very complex, with a bunch of corpses, and they were killed with a variety of weapons.
"Environmental causes multiply rather than add up, so it's hard to pick one thing out," Payne says. This is not a failure of science, but rather an accusation against our demand for simple answers.