A research team led by Prof. SHEN Yan’an from the University of Science and Technology of China of the Chinese Academy of Sciences conducted a systematic study of the interglacial stratigraphy in South China by means of high-precision sulphur and mercury isotope analyses. The team suggested that the melting of the "Snowball Earth" induced large-scale volcanic activities, and provided evidence that the gradual oxidation of interglacial oceans created favorable environmental conditions crucial for the evolution of early and complex life. The study was published in Science Advances. 

To investigate the changes in the Earth's surface environment and climate system following the thawing of the "Snowball Earth," the team focused on the Datangpo Formation in South China which represents an important source of large and even super-large sedimentary manganese deposits in China, and provides a nearly complete record of the climate and environmental changes between two "Snowball Earth" events. 

Based on multiple field surveys and investigations, the team selected a drill core from the Datangpo Formation, spanning hundreds of meters, for geological, stratigraphic, and geochemical analyses. They found that during the initial stages of the "Snowball Earth" thawing, the chemical composition of seawater was primarily influenced by hydrothermal venting on the seafloor. This indirectly reflects the fundamental differences between the ocean during the "Snowball Earth" period and a normal ocean. During that time, the exchange and circulation of substances among the ocean, atmosphere, and land were severely limited. 

The variations in non-mass-dependent mercury isotopes provided evidence for the intensification of volcanic activity during the deglaciation of the "Snowball Earth." In the light of this finding, the team proposed a new perspective that the rapid thawing of the "Snowball Earth" led to a sudden reduction in surface pressure, thereby triggering magmatic activity deep within the Earth and subsequent volcanic eruptions. 

Besides, the team identified anomalies in the sulfur isotope composition of pyrite in interglacial sediments, including slight non-mass-dependent sulfur isotope fractionation. However, the sedimentary sequence clearly indicated that this minor non-mass-dependent sulfur isotope fractionation was not causally related to volcanic activity. The team then postulates that the minor non-mass-dependent sulfur isotope fractionation was a result of the "Snowball Earth" altering the sulfur isotope composition of seawater sulfates. 

In addition, the temporal variations in sulfur isotopes demonstrated a gradual increase in sulfate concentration in interglacial seawater, indicating a progressive oxidation of the atmospheric and oceanic systems during that period. Considering the changes in atmospheric chemistry, a gradual decrease in surface temperatures, and the progressive oxygenation of the oceans during the interglacial period, the team proposed that the environmental and climatic changes on the Earth's surface during the interglacial period promoted the evolution of early complex life forms. 

The findings of this study provided significant implications for exploring contemporary extreme climate changes and the Earth's habitability.