What caused the end-Permian mass extinction?

[lpetrich]

The K-Pg mass extinction at the end of the Mesozoic Era is the best known, but the biggest Phanerozoic one ever was the Permo-Triassic (P-Tr) one at the end of the Paleozoic Era around 252 million years ago (the K-Pg one was 66 million years ago). Some 90% of marine species died in it, and some 70% of land species. Much ground-cover vegetation died, and streams changed from meandering to braided as a result.

Huge Vegetation Loss Accompanied Mass Extinction -  Permian–Triassic extinction event - "The Great Dying"

What caused it continues to be poorly understood, but some recent work sheds light on that calamity.

New insight into the Great Dying
noting
Permo–Triassic boundary carbon and mercury cycling linked to terrestrial ecosystem collapse | Nature Communications
From phys.org:

The team built a computer model that mapped chemical changes in Earth's oceans during the period of the Permian-Triassic extinction. The model tracks the cycling of the poisonous element mercury, which is emitted from volcanoes but also gets incorporated into living organisms. By tracing both the mercury and carbon cycles, and comparing to measurements in ancient rocks, the team were able to separate out biological and volcanic events.

This revealed that a massive collapse of terrestrial ecosystems cascaded organic matter, nutrients, and other biologically-important elements into the marine system.

Driver of the largest mass extinction in the history of the Earth identified
noting
Permian–Triassic mass extinction pulses driven by major marine carbon cycle perturbations | Nature Geoscience

For their study, the BASE-LiNE Earth team used a previously often neglected environmental archive: the shells of fossil brachiopods. "These are clam-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 our analyses. These shells were deposited at the bottom of the shallow shelf seas of the Tethys Ocean 252 million years ago and recorded the environmental conditions shortly before and at the beginning of extinction," explains Dr. Hana Jurikova. She is first author of the study, which she conducted as part of the BASE-LiNE Earth project and her doctoral thesis at GEOMAR.

By measuring boron-isotope concentrations in those shells, they were able to track the ocean's pH, and thus the atmosphere's CO2 content.

"With this technique, we can not only reconstruct the evolution of the atmospheric CO2 concentrations, but also clearly trace it back to volcanic activity. The dissolution of methane hydrates, which had been suggested as a potential further cause, is highly unlikely based on our data," explains Dr. Marcus Gutjahr from GEOMAR, co-author of the study.

The CO2 likely came from massive volcanic eruptions in Siberia, eruptions that produced rock formations called the Siberian Traps. The lava was fluid enough to make big sheets of volcanic rock rather than volcanoes, making a Large Igneous Province. LIP's formed elsewhere in the Solar System, like the "seas" of the Moon.

As a next step, the team fed their data from the boron and additional carbon isotope-based investigations into a computer-based geochemical model that simulated the Earth's processes at that time. Results showed that warming and ocean acidification associated with the immense volcanic CO2 injection to the atmosphere was already fatal and led to the extinction of marine calcifying organisms right at the onset of the extinction. However, the CO2 release also brought further consequences; with increased global temperatures caused by the greenhouse effect, chemical weathering on land also increased.

Over thousands of years, increasing amounts of nutrients reached the oceans via rivers and coasts, which then became over-fertilized. The result was a large-scale oxygen depletion and the alteration of entire elemental cycles. "This domino-like collapse of the inter-connected life-sustaining cycles and processes ultimately led to the observed catastrophic extent of mass extinction at the Permian-Triassic boundary," summarizes Dr. Jurikova.

Brachiopods are a kind of marine invertebrate whose shells often superficially resemble clam shells. Clams are bivalves, and brachiopod and bivalve ancestors invented their shells separately.

• Bivalves: placement: left-right, CaCO3 form: aragonite
• Brachiopods: placement: dorsal-ventral, CaCO3 form: calcite

Brachiopods were abundant in the Paleozoic, but their diversity was much reduced in the P-Tr mass extinction. They have survived to the present, however. Bivalves also lived in the Paleozoic, but they became much more abundant afterwards.

 

[repoman]

A planet wide Minamata disaster on top of a supercharged global greenhouse sounds terrifying.