At the end of the Permian period 252 million years ago, Earth was devastated by a mass extinction that wiped out more than 90% of the planet’s species. Compared to other mass extinctions, the recovery from the Great Dying was slow: it took at least 10 million years for the planet to be repopulated and begin to restore its diversity. The largest mass extinction in Earth’s history may have been triggered by a strong El Niño cycle. A deadly pulse of ultraviolet (UV) radiation may also have played a role in Earth’s largest mass extinction, fossilized pollen grains suggest.
Volcanoes spewing carbon dioxide 250 million years ago heated the climate so much that extreme El Niño events became the norm, pushing most life on Earth beyond its limits. The largest mass extinction in Earth’s history may have been caused by a powerful El Niño cycle.
New research suggests that an overload of carbon dioxide in the atmosphere led to climate change, which in turn led to the extinction of 90% of Earth’s species around 250 million years ago, at the end of the Permian period. The discovery has implications for modern climate science: Researchers don’t know how current warming will affect the El Niño-La Niña cycle, but even a small part of the disruption caused by the world’s largest extinction would make life very difficult for humanity.
Life flourished during the Permian Period (298.9 million to 251.9 million years ago). The supercontinent Pangaea was surrounded by lush forests where strange reptiles roamed alongside amphibians and buzzing clouds of insects. In the oceans, towering reefs were home to spiral nautiluses, bony fish, and sharks.
Then a series of giant volcanic rifts erupted in what is now Siberia. These rifts, known as the Siberian Traps, released huge amounts of carbon dioxide into the air. Worse, they erupted in an area rich in coal seams, which also evaporated into the atmosphere. Geological deposits from this eruption have been found in rock layers as far away as South Africa.
A geological section of the field from the study revealed extreme dryness 252 million years ago, a sign of disruptions in the El Niño-La Niña cycle. The new study suggests that volcanic eruptions in Siberia triggered extreme El Niño events that led to the end-Permian extinction, when 90% of life on Earth died out. Paul Wignall/University of Leeds
The study’s lead author, Yadong Sun, a geoscientist at the China University of Geosciences, has long compiled a database of teeth from eel-like Permian creatures called conodonts, because the teeth can provide information about ocean temperatures. His data show that across Panthalassa — the ancient ocean that was the predecessor to the Pacific — the western part of the ocean was initially warmer than the eastern part. However, this gradient weakened as the climate warmed at the end of the Permian, creating warmer temperatures in the east — just as it does in today’s El Niño events in the Pacific.
The end result, Farnsworth said, was a series of very severe, very long-lasting El Niños. Sun, Farnsworth and their colleagues modeled the effects and showed that on land, these El Niño events would have intensified the already rising temperatures caused by carbon dioxide-induced warming. Forests and the species that depended on them would have struggled and died first. Forests remove carbon dioxide from the atmosphere, so their loss allowed even more heat-trapping carbon to remain aloft.
There was a noticeable time lag between the death of marine and land fauna. Moreover, the extinction of marine biota began 17 thousand years earlier than the sharp warming of equatorial waters from 26° to 34°, which clearly exceeded the capabilities of many living creatures. This means that there was another invisible “killer” at work – perhaps a lack of oxygen in the ocean (anoxia). However, the authors of the study rejected this version, since in the era of high atmospheric oxygen saturation, ocean anoxia could hardly have caused the death of land biota, which began before the marine crisis and long before the peak of warming. Evidence of this is the disappearance of peatlands and the replacement of gymnosperm forests with shrub ecosystems tens or even hundreds of thousands of years before the death of ocean biota. Scientists have put forward several hypotheses for land extinction – from metal poisoning, ozone depletion to acid rain. But none of them could explain the full depth of the Late Permian crisis.
The team looked at short-term climate events that operate on annual and decadal timescales and can cause large fluctuations in temperature and hydrological cycles. They used the HadCM3BL model to predict global climate in the context of a sharp increase in greenhouse gas emissions, paleotemperature data, and sedimentary rock analysis to determine the equatorial sea surface temperature gradient (SST) and to build a model of the interaction between the atmosphere and the ocean.
According to the resulting model, at the end of the Permian, the zonal SST gradient in the Tethys Ocean decreased from 7–10°C to 1–4° at the boundary of geological periods. These and other major changes in ocean parameters led to a weakening of the Walker circulation, a meteorological phenomenon of mixing the lower layers of the atmosphere over the ocean in the tropics. All this caused El Niño, a fluctuation in the temperature of the upper layer of the tropical ocean.
Modern El Niño lasts for 9-12 months, while in the Pliocene they lasted for three million years. There is debate about how much global warming is intensifying this phenomenon. However, a model built by the authors of the new scientific paper showed that at the end of the Permian period, the strength and duration of El Niño increased. As a result, a very warm and extremely unstable climate was established on the planet.
During powerful El Niños, heat energy stored in the ocean spilled onto land, causing severe droughts and extreme heat waves. Today, this is happening in the equatorial zone, hitting the Amazon and central Africa.
As for marine biota, intense El Niño heat waves still cause coral reef bleaching and plankton die-offs today. At the end of the Permian, this nearly led to a planet-wide catastrophe.
A deadly pulse of ultraviolet (UV) radiation may have played a role in Earth’s greatest mass extinction, fossilized pollen grains suggest. Analysis has shown that pollen dating to the Permian-Triassic mass extinction, about 250 million years ago, produced “sunscreen” compounds that protected against harmful UVB radiation. About 80% of all marine and land species died out at the time.
For the study, published in the journal Science Advances, a team of international scientists developed a new method of using a laser beam to study the tiny grains, which are about half the width of a human hair and were found embedded in rocks discovered in southern Tibet, according to a statement.
Dimetrodon was one of the creatures that lived during the Permian period. Mark Garlick/Science Photo Library
Plants use photosynthesis to convert sunlight into energy, but they also need a mechanism to block harmful UVB radiation. In this case, the burst of radiation would not kill the plants outright, but rather slow them down, reducing their ability to photosynthesize, which would eventually make them unable to reproduce.
Experts have long suspected that the Permian–Triassic extinction, classified as one of Earth’s five major extinction events, was a response to a “paleoclimate emergency” caused by the Siberian Traps eruption, a major volcanic event in what is now Siberia. The catastrophic event pushed carbon plumes buried deep within the Earth into the stratosphere, triggering global warming that “led to the collapse of Earth’s ozone layer,” according to the researchers.
A pollen grain used in the study, about half the width of a human hair. Liu Feng/Nanjing Institute of Geology and Palaeontology
In their study, the researchers also found a link between the surge in UVB radiation and how it altered the chemistry of plant tissues, leading to a “loss of insect diversity,” in which plant tissues became less palatable to herbivores and less digestible.
Because the plant leaves had less nitrogen, they were not nutritious enough for the insects that ate them. This may explain why insect populations plummeted during this extinction. Insects often survive mass extinctions unscathed, but not during this extinction.
After the Great Dying, life on Earth took millions of years to recover. Microorganisms may explain the slow recovery after this period.
At the end of the Permian period 252 million years ago, Earth was devastated by a mass extinction that wiped out more than 90% of the planet’s species. Compared to other mass extinctions, recovery from the Great Dying was slow: it took at least 10 million years for the planet to be repopulated and begin to restore its diversity.
Now, scientists may have figured out what delayed Earth’s recovery. A group of tiny marine organisms called radiolarians disappeared in an extinction event. Their absence radically altered marine geochemistry, leading to the formation of a type of clay formation that released carbon dioxide. This release of carbon dioxide kept the atmosphere warm and the oceans acidic, thereby slowing the recovery of life, the scientists explained in a paper published in the journal Nature Geoscience.
Study co-author Clement Bataille, now a professor of earth and environmental sciences at the University of Ottawa in Canada, told Live Science that such extreme conditions had not been seen on Earth for hundreds of millions of years, before life emerged everywhere.
“It just shows how much we don’t know about these biogeochemical cycles and how a small change can throw a system out of balance very quickly,” Bataille said.
Bataille worked on the study as a postdoctoral fellow in the lab of Xiao-Ming Liu, a geochemist at the University of North Carolina at Chapel Hill. The researchers were trying to understand changes in Earth’s climate during the late Permian period (298.9 million to 251.9 million years ago) and the early Triassic period (251.9 million to 201.3 million years ago). The team wanted to study a process called chemical weathering — when rocks on land break down and release calcium, which flows into the oceans. There, the calcium combines with carbon dioxide (CO2) to form carbonate rocks. The warmer the climate, the faster the weathering occurs, because chemical reactions happen faster at higher temperatures, and more flowing water means more erosion. This creates a feedback loop that controls global temperatures: When it’s warmer and weathering happens faster, more CO2 flows into the sea and gets locked in ocean rocks, helping to cool the climate. As the climate cools, weathering slows and less CO2 is locked into ocean rocks, thus preventing too much cooling.
But there is another process that can happen in the ocean called reverse weathering. This happens when the mineral silica is abundant and forms new clays on the ocean floor. During reverse weathering, these clays release more CO2 than the carbonate rocks can hold.
Silicon is not very abundant in modern oceans because it is consumed by tiny planktonic organisms to build their shells, so reverse weathering does not occur often. Likewise, during the Permian, tiny organisms called radiolarians consumed almost all the silicon, thereby keeping reverse weathering to a minimum.
But all that may have changed at the end of the Permian and beginning of the Triassic. At that point, silica-rich rocks containing countless radiolarian shells disappeared, suggesting that radiolarians may have gone extinct. At the same time, the balance of certain types of molecules in oceanic rocks was disrupted, Bataille, Liu, and their colleagues found.
The researchers studied the ratios of lithium isotopes. Isotopes are versions of an element with slightly different atomic masses than normal because their nuclei contain different numbers of neutrons. Because of their different weights, different lithium isotopes are absorbed in different ratios when new clays form, which occurs during reverse weathering. The researchers found that some lithium isotopes virtually disappeared from the ocean just before the Great Dying and were not restored for about 5 million years during the Triassic. That paints a picture of a world in which the loss of radiolarians left the ocean overflowing with silica, allowing reverse weathering to occur, Bataille said. The CO2 released by reverse weathering could have suppressed the CO2-trapping chemical weathering occurring at the time and, in turn, kept the climate superheated. Life would have struggled under those conditions.
This is the first direct evidence that reverse weathering occurred at this time, said Hana Jurikova, a marine biogeochemist at the University of St Andrews in Scotland. Jurikova was not involved in the study, but she wrote an editorial accompanying the paper in the journal Nature Geoscience.
