Hardly anything was left of the previously colorful world – the Permian era ended with the worst mass extinction in the history of the earth. New study results now show how the drama unfolded around 252 million years ago: Studies of shellfish fossils and model simulations show how a greenhouse catastrophe as a result of gigantic volcanic eruptions made life like hell. A cascade of interlocking processes ultimately led to the catastrophic extent of mass extinction, say the scientists.
The end of the world of dinosaurs at the end of the Cretaceous Period is the most famous mass extinction in Earth’s history – but a much worse one had happened much earlier: around 252 million years ago around 96 percent of marine life and around 75 percent of land life disappeared within a few millennia. This mass extinction marks the end of the Permian Age and the beginning of the Triassic epoch. The trigger for the process is the strong volcanism at the end of the Permian Age, which is reflected in gigantic deposits of flood basalt in Siberia.
How did the hellish drama go?
The release of greenhouse gases during these volcanic eruptions, but also of large amounts of methane from the seabed, are discussed in this context as a trigger of the Permian Triassic extinction. However, there are different views among scientists on the exact causes and the sequence up to the mass extinction on land and in the sea. Now an international team is presenting a conclusive model of the catastrophic processes 252 million years ago.
For their study, the scientists used a special kind of environmental archive: the fossil shells of so-called brachiopods. “These are shell-like organisms that have existed on earth for more than 500 million years. We were able to use well-preserved brachiopod fossils from the southern Alps for the analyzes. These shells were deposited on the floor of the shallow shelf seas of the Tethys Ocean 252 million years ago and record the environmental conditions shortly before and at the beginning of extinction, ”explains first author Hana Jurikova from the GEOMAR Helmholtz Center for Ocean Research in Kiel.
In the fossil shells, the scientists recorded various isotopes of the element boron. As they explain, the results reflect the development of the pH value in the ocean 252 million years ago. The signatures of the boron isotopes could thus give indications of ocean acidification, as it is also emerging as a result of today’s increase in carbon dioxide concentrations in the earth’s atmosphere. It is known that the pH value of water is closely linked to the CO2 content of the air. The scientists explain that the findings from the fossil shells enabled the reconstruction of the changes in the atmosphere at the end of the Permian era.
Cascade of doom is looming
“We were not only able to understand the development of the CO2 concentration, but also clearly trace it back to volcanic activity,” says co-author Marcus Gutjahr from GEOMAR. “The dissolution of methane hydrates, which was discussed as a further cause, is very unlikely based on our data,” emphasizes the scientist. The results show that the massive volcanic eruptions from the then active flood basalt province “Siberian Trapps” released immense amounts of CO2 into the atmosphere over several millennia. This caused severe acidification of the seawater as well as an intense greenhouse effect in the late Permian world.
The team also fed the findings from boron and other carbon isotope-based investigations into a computer-based geochemical earth model. It illustrated how warming and ocean acidification were damaging calcifying organisms. Yet another blow followed: with the climatic changes on earth, the weathering of rocks on land increased. In this way, more and more nutrients reached the oceans via the rivers, and these were eventually overfertilized. Large-scale oxygen deficiency and changes in entire material cycles were the result, according to the models. “We are dealing with a cascading catastrophe in which the rise in CO2 in the atmosphere triggered a chain of events that, one after the other, killed almost all life in the seas,” summarizes Jurikova.
“We have now succeeded in reconstructing the environmental processes in detail 252 million years ago,” says co-author Anton Eisenhauer from GEOMAR. “A better understanding of past environmental processes can also help us to better assess current and future developments,” says the scientist with a view to the currently rising CO2 concentrations in the atmosphere. Jurikova adds: “The effects of the former volcanic eruptions are not directly comparable with the carbon emissions of mankind, because all modern reserves of fossil fuels are far too small to release as much CO2 over thousands of years as was released 252 million years ago” . However, it is becoming apparent that we are ensuring a much faster release today, the researcher emphasizes: “The CO2 emission rate of mankind is fourteen times higher today than the annual emission rate at the time when the largest biological catastrophe in the history of the earth took place,” says Jurikova.
Source: GEOMAR, Helmholtz Center Potsdam – GFZ German Research Center for Geosciences, specialist article: Nature Geoscience, doi: 10.1038 / s41561-020-00646-4