Core Insights - An international team led by researchers from the Chinese Academy of Sciences has innovatively used iron isotopes as a "paleothermometer" to directly measure ocean temperatures during the "Snowball Earth" period approximately 700 million years ago, revealing that local ocean temperatures could drop to as low as -15°C with extremely high salinity [1][2]. Group 1: Research Findings - The study published in "Nature Communications" indicates that during the "Snowball Earth" period, the ocean was entirely covered in ice, with temperatures significantly lower than previously estimated [1]. - The research team successfully decoded the ocean temperature signals by analyzing iron isotopes in ancient iron-rich sedimentary rocks, which are key to understanding historical ocean temperatures [1]. - The iron isotopes from this period showed a "positive shift," indicating lower temperatures, with the signal being more pronounced at lower temperatures [1]. Group 2: Salinity Impact - The study found that despite the extremely low temperatures, seawater did not completely freeze due to the high salinity levels, which were over four times that of modern seawater, lowering the freezing point to approximately -11°C [2].

Core Findings - The research led by Chinese scientists provides direct quantitative evidence of ocean temperatures during the "Snowball Earth" period approximately 700 million years ago, revealing that local ocean temperatures could drop to around -15°C, with salinity levels significantly higher than modern seawater [1][2] Group 1: Research Methodology - The research team utilized iron isotopes from ancient "iron formations," which are sedimentary rocks composed of alternating iron-rich and silica-rich layers, to determine the extreme low-temperature environment of the "Snowball Earth" [2] - The iron isotope values from this period were found to be systematically positive compared to any other period in geological history, indicating an extremely low-temperature environment [2] Group 2: Environmental Conditions - The estimated temperature during the formation of "iron formations" in the "Snowball Earth" period was approximately -15±7°C, which is nearly 20°C lower than the coldest modern deep-sea temperatures [2] - The research confirmed that the salinity of the ocean water at that time was extremely high, which could lower the freezing point to about -11°C, corroborating the temperature estimates [2] Group 3: Implications of Findings - This groundbreaking research provides quantitative evidence for the extreme cold marine environment during the "Snowball Earth," suggesting the possibility of unique microenvironments existing under global ice cover [1] - The findings offer new insights into the survival mechanisms of early life in extreme climates and hold significant reference value for understanding drastic climate changes on Earth [1]