Researchers link Earth's largest mass extinction to volcanic activity

Researchers Link Earth's Largest Mass Extinction to Volcanic Activity

Scientists have reconstructed the sequence of events that led to the "Great Dying," the most severe environmental crisis in geologic history. Occurring approximately 252 million years ago at the transition between the Permian and Triassic periods, the event decimated an estimated 70% of terrestrial species and between 81% and 96% of marine species. Recent findings published in Nature Geoscience and the Proceedings of the National Academy of Sciences identify a surge of volcanic activity as the primary catalyst for this collapse.

The crisis was driven by the movement of magma under the Earth's crust in a volcanic region known as the Siberian Traps. Research supported by the EU-funded BASE-LiNE Earth project indicates that substantial carbon degassing from Siberian sill intrusions — bodies of igneous rock formed between other rock layers — triggered a catastrophic chain of events. This release of carbon dioxide (CO2) into the atmosphere caused ocean acidification, higher global temperatures, and increased chemical weathering on land.

According to researchers, this process created a domino-like collapse of life-sustaining cycles. The initial acidification was fatal to much marine life, while subsequent warming led to large-scale deoxygenation and scattered sulfide poisoning of the oceans. While some scientists previously suggested the dissolution of methane hydrates as a potential cause, co-author Dr. Marcus Gutjahr stated that such a cause is highly unlikely based on the project's data.

The Biological Divide: Winners and Losers

Not all species were affected equally. A Stanford-led study focused on the taxonomic selectivity of the extinction, exploring why some animal groups survived while others vanished. The researchers found that the groups hit hardest were those with metabolisms least able to tolerate warm, oxygen-poor water.

The ancient oceans were once dominated by slow-metabolizing, immobile, filter-feeding animals, including sea lilies (crinoids) and brachiopods, clam-like organisms. Brachiopods were nearly wiped out, with only around 400 species existing today. In contrast, more mobile animals with faster metabolisms, such as mollusks (clams and snails), fish, and echinoderms like sea urchins, fared better. Approximately half of the mollusks died off, allowing them and other athletic fauna to dominate the oceans thereafter.

To reach these conclusions, the Stanford team monitored the oxygen use of various animal groups in laboratory chambers. They discovered that while Paleozoic fauna can survive in water with less oxygen than modern groups, their slow metabolisms cannot keep pace when temperatures rise. Modern fauna, possessing more robust muscles and gills, can meet the increased oxygen requirements associated with warming.

Senior author Erik Anders Sperling described the findings as the final nail in the coffin regarding the cause of the extinction, noting that warming and oxygen loss were the key drivers. While ocean acidification contributed, Sperling noted it was nowhere near the most devastating factor.

Regional Collapses and the "Smoking Gun"

While the volcanic trigger is confirmed, new research challenges the idea that the environmental collapse happened globally and simultaneously. A study led by Jianbo Chen and Isabel P. Montañez suggests that terrestrial ecosystems collapsed regionally and in stages.

Analyzing a 671-meter-long drill core (HK-1) from an ancient tropical peatland in Southwest China, the team found that local ecosystems there collapsed several hundred thousand years after similar collapses occurred in high-latitude areas, such as the Sydney Basin in Australia. Chen described this time lag as a crucial clue, suggesting the die-offs were a series of regional collapses rather than a single global hammer blow.

The team searched for a smoking gun in the form of a mass-independent isotope anomaly, a geochemical fingerprint created when volcanic sulfur is blasted into the stratosphere and hit by UV radiation. However, this signature was nearly absent in the HK-1 core. Instead, the researchers found sulfur remnants coming from non-volcanic sources, specifically the catastrophic erosion of deforested soils.

Modern Implications

The parallels between the Permian-Triassic boundary and current climate trends have led researchers to issue a warning. Sperling noted that the world preceding the Great Dying was relatively cool and well-oxygenated, similar to the modern era, before a giant injection of CO2 occurred.

During the Great Dying, temperatures increased 8-12° Celsius over thousands of years. Current projections suggest temperatures could be 1.5-4° Celsius warmer than pre-industrial times by 2100, a change occurring over just 100-200 years. Sperling warned that in worst-case scenarios, the planet is on track for levels of warming similar to those of the Permian-Triassic.

Following these discoveries, researchers plan to examine more marine animal groups to further understand the interplay between warming, acidification, and oxygen loss. Additionally, the team led by Chen intends to analyze the HK-1 core layers from before the extinction to determine if the ecosystem was already unstable before the final collapse, with plans to investigate other sites in North China and the Karoo Basin in South Africa to build a high-resolution global timeline.