The Great Dying Event Of The Permian Epoch: A Message For The Present From The Distant Geologic Past

 

It's common knowledge that trees absorb carbon dioxide and help sustain life on Earth, but their profound influence on stabilising the planet's climate runs far deeper than most imagine. A recent research revealed that forests have been quietly offsetting ancient carbon stored in terrestrial landscapes that leak into the atmosphere via rivers. However, it’s the fate of tropical rainforests that now draws urgent attention. A study of the Permian-Triassic extinction, dubbed the "Great Dying," shows that the collapse of ancient forests triggered a global hothouse effect, which lasted millions of years.

 

This discovery serves as a reminder from the past and underscores how losing modern tropical forests could profoundly destabilise climate systems far into the future, highlighting their indispensable role as planetary climate guardians. The Permian Period was the final period of the Palaeozoic Era, lasting from about 298.9 to 251.9 million years ago. It followed the Carboniferous Period and preceded the Triassic Period, marking the beginning of the Mesozoic Era. Noted for the formation of the supercontinent Pangaea, the Permian to Early Triassic (252-247 million years ago) was a time of significant climatic shifts that caused global environmental stress, culminating in the severest of the five extinction events in Earth's geological history, known as the "Great Dying".

 

The massive volcanic eruptions in Siberia and the emission of carbon during that period have played a crucial role in triggering the extinction event. The source of the Siberian Traps basalt is believed to be a mantle plume at the base of the crust, which erupted through the Siberian craton. The Permian-Triassic mega greenhouse condition resulted in the loss of more than 80 per cent of marine and terrestrial life. During volcanic eruptions, vast amounts of greenhouse gases, including water vapour, carbon dioxide, and sulphur dioxide, are released. Although sulphur dioxide is not a greenhouse gas, it can cause acid rain and air pollution, and it reacts with atmospheric components to produce aerosols that scatter radiation, thereby trapping heat.

 

Volcanoes also release thermogenic gases generated when magma intrudes into sedimentary rocks, releasing trapped gases like methane, a significant greenhouse gas. The massive disruption to the carbon cycles, high air and sea temperatures, and an acidic ocean signal rapid additions of greenhouse gases to the atmosphere. But the question that puzzled researchers was why the global hot-house conditions persisted for more than 5 million years. Why Recovery Took So Long The increased global silicate weathering would have been expected to bring CO2 levels back to pre-volcanism levels within approximately 100,000 years.

 

This occurs through a chemical process where rainwater, slightly acidic from dissolved CO2, reacts with silicate rocks, transforming them into stable carbonate minerals—an efficient natural way of carbon sequestration, and stabilising the global climate. Therefore, the prolonged recovery period for oceanic and terrestrial ecosystems to return to their original states remained an intriguing unanswered question. In a paper—Early Triassic super-greenhouse climate driven by vegetation collapse—published in Nature Communications, a group of researchers from the China University of Geosciences, Wuhan, and Leeds University in the United Kingdom have shed more light on this extended period of extinction. The classic rock sections displaying biotic evidence of the Permian-Triassic (P-Tr) boundary in Southwest China (eastern Yunnan and western Guizhou) are key areas providing insights into the extinction event on land.

 

The team conducted extensive field studies at sites in China that exposed Permian rock outcrops containing fossil records, and they were able to reconstruct maps of changes in plant productivity during the Permian-Triassic boundary. They conclude that the collapse of the tropical forest during that period triggered a climate tipping point. Their findings demonstrated that reduced vegetation decreased the Earth’s capacity for carbon sequestration, thus extending the duration of high carbon dioxide levels. Using an extensive archive of fossils, they reconstructed the distribution maps of plants and trees before, after, and during that time across various regions of the world. The data from these studies confirmed that vegetation took a longer time to establish, thereby lowering the Earth’s ability to absorb carbon from the atmosphere. This explains why the Permian-Triassic extinction event lasted for 5 million years, longer than the usually expected period needed for recovery.