Peng Liu and his PhD supervisors Profs. Yonggang Liu and Yongyun Hu published a paper entitled “Large influence of dust on the Precambrian climate” in Nature Communications. This study demonstrates that enormous amount of dust on the early Earth could have cooled the global surface temperature by ~10°C.
Their climate simulations enabling dust show that atmospheric dust loading might have been an order of magnitude higher than that of modern, before the emergence of terrestrial plants. Such heavy dust loading strongly scatters sunlight, reducing the solar radiation that can reach the surface. As a result, the global mean surface temperature drops by ~10°C. In comparison, the impact of dust on modern climate is less than 0.5°C. These results show that dust was crucial in deep paleoclimate, but was generally ignored in previous studies. Meanwhile, large amount of dust would deposit into the oceans, providing abundant nutrients for marine life. The deposition of dust may also lead to the formation of vast sedimentary layer, providing a reasonable explanation for the planar-laminated thin-bedded sediment in geological records.
The terrestrial plants on the earth did not appeared until ~500 million years ago. Before that, there were some lichens and mosses, and only microorganisms such as cyanobacteria for even earlier time period. Without protection of plants, soil would be lifted up into the air by winds easily. In present day, most land (~70%) are covered by plants, and dust emission occurs only in limited desert area. During the relative cold Last Glacial Maximum (LGM, 21,000 years ago), dust loading was about twice as high as in present day (Fig. 1) due to reduction of vegetation cover, declining of sea level and erosion of ice sheets, which all contributed more dust sources. Geologists generally believe that the atmospheric dust loading was high during the Precambrian (before 540 million years ago), but there has been no solid observational evidence. This study provides quantitative evidence for the first time from a simulation perspective.
Fig.1 Simulated atmospheric dust loading during the Precambrian, Preindustrial, and LGM. The solid black curves represent the outlines of continent in various periods. The dust loading for LGM represents only a possible scenario obtained by numerical simulation.
Within some Precambrian strata, such as the Revett Formation in Montana, United States, there often exists spectacular planar-laminated thin-bedded sedimentary units, stretching for hundreds of kilometers without any ups and downs (Fig. 2). Some people have argued that they were formed by sheetflooding. However, existence of many thin layers in these sedimentary units extending for hundreds of kilometers without interruption makes such explanation unconvincing. Other people have argued recently that these sedimentary units could have be formed by dust deposition, because the spatial scope of dust storms is generally much larger than that of flooding. Simulations by Liu et al. provide good support for the latter explanation.
Fig.2 Sediments in Montana, USA (focusing on the lowest layers), formed around 1.46 billion years ago. This picture is from Winston (2016，doi: 10.1130/2016.2522(01)).
The first author of this study, Peng Liu, is a Ph.D. student who just graduated from the Department of Atmospheric and Oceanic Sciences, Peking University. Assistant Professor Yonggang Liu and Professor Yongyun Hu are the corresponding authors. Other collaborators include the associate Professor Yiran Peng and Ph.D. student Mingxing Wang from Tsinghua University and the Chief Scientist of CESM, Jean-Francois Lamarque, at NCAR in the USA. The project was funded by the National Natural Science Foundation of China. The study can be found at: https://rdcu.be/b6Mj8
