Did volcanic eruptions cause the fifth mass extinction?

The fifth mass extinction event, which occurred at the end of the Cretaceous period (about 66 million years ago), ended the more than 150 million-year-long dinosaur era on Earth and paved the way for the rise of mammals.

Currently, there is still a heated debate about the cause of this mass extinction. Among them, the two mainstream views are the Deccan basalt eruption in India and the asteroid impact. The timing of the Deccan basalt eruption and its impact on the global environment are also hot topics in this field.

To this end, the Nanjing Institute of Geology and Paleontology, Chinese Academy of Sciences (hereinafter referred to as Nanjing Institute of Paleontology), together with research teams from Tianjin University, China University of Geosciences (Beijing) and other institutions, conducted a detailed study of the records of the first eruption of the Deccan volcano in East Asia and the response of the lake environment and biota to this extinction event. The relevant research results were published online in Geology on July 18.

Wang Bo, the corresponding author of the paper and a paleontologist at Nanjing, introduced that about 150,000 to 300,000 years before the mass extinction, the Deccan Igneous Province emitted a large amount of greenhouse gases such as carbon dioxide through intrusion and eruption, which may have caused global warming of 2 to 5°C. The academic community calls it the Late Maastrichtian Warming Event.

"Elucidating the mechanism and process of this warming event can provide important evidence for understanding the cause of the end-Cretaceous mass extinction, and also provide new insights into our understanding of the coupling relationship between the carbon cycle and the greenhouse Earth." Wang Bo pointed out, "At present, our understanding of this event is very limited. In particular, whether records related to the first eruption of the Deccan volcanoes can be found in terrestrial sediments, and how the warming event at the end of the Maastrichtian affected the terrestrial ecosystem, these two questions have been lacking key evidence."

The research team used core data from two wells in Shandong Province that span the Cretaceous/Paleogene (K/Pg) boundary to conduct research on mass extinction events based on high-precision biostratigraphy, paleoecology and geochemistry methods. The relevant research results provide strong evidence for the coupling relationship between the late Maastrichtian warming event and the first eruption of the Deccan volcanoes, and show that the warming event also had a significant impact on the lake environment and biota.

Li Sha, the first author of the paper and an associate researcher at the Nanjing Institute of Paleontology, said that the two drill cores in this study represent two different sedimentary environments, the clastic rock deposits in the Jiaolai Basin and the carbonate rock deposits in the Pingyi Basin. Since a large amount of mercury released by volcanic eruptions will be recorded in the strata, mercury records are widely used as tracers of volcanic activity. During the late Maastrichtian warming event before the Cretaceous/Paleogene boundary, samples from both boreholes showed strong mercury enrichment.

In order to explore the impact of Deccan volcanic activity on lake environment and biota, the research team also conducted carbon isotope and paleontological studies, and found that the organic carbon isotopes in the Jiaolai Basin and the inorganic carbon isotopes in the Pingyi Basin simultaneously showed strong negative deviations, indicating that the major pulse of the Deccan Large Igneous Province had a huge impact on mercury and the global carbon cycle.

The study also found that the biota of the two lakes had a significant response to the warming event. The speciation of charophytes and ostracods in the Jiaolai Basin and Pingyi Basin was obvious, and the biodiversity increased. In the ocean, the planktonic foraminifera species experienced partial extinction, dwarfism, and the prevalence of disaster species, which shows that the warming event at the end of the Maastrichtian period affected the marine and terrestrial ecosystems at the same time through different mechanisms.

"Our results show that the Deccan volcanic activity kept the Earth in relatively warm climate conditions, and this warming may have brought the global biogeochemical cycle closer to the critical point of a runaway greenhouse environment. This may have been the background condition for the mass extinction at the end of the Cretaceous," said Lisa. "The results provide new evidence for our understanding of the relationship between volcanic carbon emissions and a greenhouse Earth, and also provide a reference for understanding the impact of today's global warming on lake environments and biota."