About 252 million years ago, more than 81 percent of animal life in the oceans and 89 percent of animal life on land went extinct. This event, called the "end-Permian mass extinction" (EPME), represents the greatest catastrophe in the history of life on Earth. The proximate driver of the event has long been a mystery.
However, a new study led by scientists from the Nanjing Institute of Geology and Palaeontology of the Chinese Academy of Sciences (NIGPAS) and Nanjing University has now revealed that Felsic volcanism in South China drove the EPME.
The study was published in Science Advances on Nov. 17.
Previous studies suggested that volcano eruptions in Siberia, an event called the "Siberian Traps large igneous province (STLIP)," was the single major driver of the mass extinction event. The support for this argument comes from the observation that STLIP was large enough to perturb the global environment.
The team, however, noted that temporal links between the mass extinction and volcanism were largely based on sedimentary records from South China, while the Siberian region does not contain direct evidence of biological extinction. The scientists also noted that more than one-third of the erupted volcanic rocks and the entire STLIP intrusive magmatism postdated the end-Permian mass extinction horizon.
Therefore, the team wanted to determine if volcanic eruptions from other regions could help explain the EPME. In this study, the team focused on terrestrial ecosystems, which were decimated during the EPME.
Typically, scientists identify ancient volcanic eruptions by looking at the abundance of volcanic rocks preserved on Earth's present-day surface, and anomalies of elemental mercury in ancient sedimentary rocks. But volcanic rocks can be weathered or covered and disappear from the Earth's surface. Furthermore, enrichment of elemental mercury in sedimentary rocks does not always indicate the presence of volcanic eruptions.
To overcome this, the team pioneered a new and more efficient approach. By studying variations in elemental copper and its isotopes recorded in sedimentary rocks, the team was able to infer large-scale volcano eruptions near the studied outcrops. These sediments, collected in modern-day South China, recorded the entire EPME.
The resulting extreme elemental copper enrichment and the associated anomalously light isotopic compositions in the EPME interval in South China gave the answers the researchers were looking for. They were able to show that large-scale eruptions near the South China Block were synchronous with the EPME.
The new study has strengthened the case that the STLIP may not have been the sole trigger for the extinction.
"This finding provides critical new insights into mechanisms that led to the extinction of animal life both in the ocean and on the land. We suggest that felsic volcanism in South China was a key contributor to the environmental deterioration that led to the end-Permian mass extinction," said Prof. ZHANG Hua from NIGPAS, the first author of the study.
The discovery calls attention to the possible effects of modern climate change. The new study estimated that volcanic SO2 injections would have produced several degrees of rapid cooling before or coincident with the more protracted global warming caused by CO2 injections. Such swings in end-Permian climate from volcanic carbon and sulfur outgassing could create deadly environments for ecosystems.
"One of the most interesting and worrying things about the end-Permian extinction is how similar those events are to what is happening today," said corresponding author Prof. SHEN Shuzhong from Nanjing University. "Similar to what happened during the end-Permian period, the modern Earth is facing rapid climate warming due to anthropogenic CO2 emissions."
Fig. 1 Photographs and photomicrographs of Cu-rich sulfide and charcoal from the terrestrial Permian-Triassic transition. (Image by NIGPAS)
Fig. 2 Schematic showing the formation process of copper-rich deposits within the EPME interval in South China. (Image by NIGPAS)
LIU Yun, Propagandist
Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences
Nanjing, Jiangsu 210008, China