Researcher Shen Jiaheng of the Institute of Earth and Space has made important progress in the study of mass extinction at the end of the Permian

With the support of the National Natural Science Foundation of China (grant number: 42072034 and 41888101), researcher Shen Jiaheng of the School of Earth and Space Sciences of Peking University has made important progress
in the study of mass extinction at the end of the Permian.
The results of the study are "Early and late phases of the Permian–Triassic mass extinction marked by different atmospheric_CO2.
" regimes", published online on October 3, 2022 in the internationally renowned journal Nature Geoscience, IF: 21.
531, Shen Jiaheng is the first and corresponding author of the research work, and cooperates with China University of Geosciences (Wuhan), Texas Agriculture and Industry, and Harvard University
.

Has the Earth entered the "sixth mass extinction" today? Is humanity experiencing rising carbon dioxide concentrations, rapid global warming and deteriorating ecological environment? To answer this question, it is not enough to rely on the short-scale data that we humans observe
.
Studying the Deep Time record, the mass extinction event at the end of the Permian, can help us find answers
.

The mass extinction at the end of the Permian period, which occurred about 250 million years ago, is the largest biological cluster extinction in the history of life on Earth, about 90% of marine species and 70% of land species are extinct, which is a rare geological abrupt event
in which marine and terrestrial ecosystems face collapse at the same time.
Large-scale volcanic activity in Siberia is believed to be the "culprit" of this event, and a series of climatic and environmental changes (global warming, ocean hypoxia, acidification, hypercapnia, etc.
) have caused the destruction of organisms
.
However, this series of clitic, environmental and biological evolutionary mechanisms need to be further accurately determined
.
In response to this problem, this study provides a direct geological record of climate change and the evolution of paleomarine primary productivity community structure by measuring and analyzing the cross-sectional samples of Guangyuan Shangji Temple, and further interprets the different mechanisms
of biological extinction in this period in combination with the model.

In response to climate change during this period, Shen Jiaheng quantitatively reconstructed the atmospheric carbon dioxide concentration during this period using the monomer carbon isotope of the ancient chlorophyll biomarker compound (Figures 1 and 2).

The reconstruction results showed that the first act was extinct and the_pCO2 was the lowest; Subsequently, pCO2 rose rapidly and entered a period of slow rise, and this high_pCO2 continued until the second act of the Early Triassic extinction, reaching its highest value; After that,_pCO2 begins to decline
slowly.
This reconstruction details the different_pCO2 characteristics
of the two acts of extinction.
Biomarker monomer nitrogen isotopes were used to quantitatively reconstruct the evolution of marine primary productivity community structures (bacteria and eukaryotes) during this period (Figures 1 and 2).

The reconstruction results show that at the time of the extinction of the first act, the marine primary production community was dominated by eukaryotes; At the time of the extinction of the second act, cyanobacteria dominated the marine primary production community
with an absolute advantage of ~100%.

Fig.
1: Whole rock carbon and nitrogen isotopes and monomer carbon and nitrogen isotopes of biomarker compounds determined by research and analysis

Fig.
2: Atmospheric carbon dioxide concentration and evolution of paleomarine primary productivity community structure during the late Permian mass extinction based on monomer isotope reconstruction of biomarker compounds

Combined with the Long-term Ocean-atmosphere-Sediment CArbon cycle Reservoir Model (LOSCAR), the authors reshaped the response mechanisms
to climate and carbon cycle disturbances during this period.
The low_pCO2 at the time of Act I extinction is attributed to the large amount of fresh weatherable material produced by the large eruption of large basalt rocks in early Siberia (~300kyr before Act I extinction ~ 300kyr) rather than strong outgasping
。 The enhancement of pulsed weathering capacity at this stage can effectively inhibit the accumulation of carbon dioxide in the atmosphere, and bring a large amount of nutrients and minerals into the ocean, increase the alkalinity of the ocean, buffer the marine carbonate balance system and the change of seawater pH value.
The large input of nutrients leads to eutrophication of the oceans, which promotes eukaryotic algae blooms, and this condition accompanied by high-productivity exports leads to a short and severe hypoxic environment in the oceans, which leads to the extinction
of organisms.

Then, the continuous action of prolonged Siberian volcanic activity depletes the surface weatherable material, causing the silicate weathering feedback to fail and lose the ability to
regulate atmospheric carbon dioxide.
This tipping point (Act I extinction) marks the beginning of atmospheric carbon dioxide accumulation and the failure of the ocean's buffering capacity; At the same time, nutrient fluxes are drastically reduced, resulting in a decline in productivity and alleviation
of ocean hypoxia.
After this tipping point, carbon dioxide rises rapidly, the climate warms, and ocean stratification intensifies; At the same time, the nutrient-poor environment of the sea has prompted cyanobacteria to completely replace eukaryotic algae
with absolute dominance.
As a result, the collapse of production communities at the bottom of the marine food chain and the weakening of productivity export fluxes eventually led to persistently high atmospheric carbon dioxide concentrations and ocean acidification in the early Triassic period, leading to Act II extinction
.
The LOSCAR model also quantitatively validates that long-term high_pCO2 from the Early Triassic was not only caused by volcanic activity, but fundamentally by changes in the structural properties of marine ecosystems (Figure 3).

In addition, the authors used the LOSCAR model to reconstruct possible carbon emission scenarios for this period: total emissions of about 5,000 PgC (excluding early Siberian volcanism), concentrated in the P-Tr boundary period, lasting about 200 kyr
.
In addition, the possible carbon source composition of this period: 40% from mantle sources from volcanic eruptions and 60% from large and lighter carbon sources
released by high-temperature magma intrusion into the organic-rich layer.

Figure 3: LOSCAR simulation results

Based on the above, this study proposes that the two-act mass extinction at the end of the Permian period has fundamentally different extinction mechanism characteristics
.
The first act is characterized by eutrophication and lack of oxygen leading to the extinction of habitat loss, while the second act is the extinction
of extreme heat, hypercapnia, and food web collapse.
This result helps explain why the mass extinction at the end of the Permian period was the largest
in Earth's history.

UAV overhead research profile extinction layer (Photographed by: Xiao Lizhe, Ma Youren, students of the Academy of Earth and Air)