A study published in Science Advances on December 8, 2023, by Yousong Cao, Matthew Bowker, Manuel Delgado-Baquerizo, and Bo Xiao, highlights the role of biocrusts—living layers made up of cyanobacteria, mosses, lichens, and other microorganisms—in preserving parts of the Great Wall of China. These biocrusts cover 67 percent of the studied sections of the wall, offering a natural defense against erosion. The research found that the compacted earth beneath these biocrusts is significantly more resistant to erosion than exposed soil, with strength gains ranging from 37 to 321 percent, depending on the type of resistance measured. The Great Wall, built over centuries starting in 221 BCE, is constructed primarily from stone and compacted earth. Many of the sections examined in the study are made of compacted earth, which is particularly vulnerable to erosion from rain and wind. The Resoil Foundation, an organization focused on soil health, notes that biocrusts are common in arid and semi-arid regions and are often overlooked as a valuable natural resource. These crusts help stabilize the soil and protect it from the elements. The researchers conducted extensive field surveys and analyzed laboratory samples of the biocrusts. Their findings suggest that the crusts act as a sacrificial layer, absorbing damage, and also function as a drainage system. The strength of the biocrusts comes from the secretion of complex polymers that form a network of cementing substances, biological filaments, and soil aggregates. This natural process enhances the structural integrity of the compacted earth beneath. The study also notes that the effectiveness of biocrusts in reducing erosion depends on factors such as the type of crust, local climate, and the structure of the wall. While the summary does not specify which parameters decreased by 48 percent or 2 percent, these details are available in the full open-access article. The research challenges the common practice of cleaning the wall, as scrubbing could remove the protective biocrust layer. Instead, the researchers propose a conservation method that works with nature, potentially offering an affordable and long-lasting solution. Ecologist Nichole Barger of The Nature Conservancy called the study "innovative and creative," and Archaeology Magazine suggested the findings could help preserve other similar historical structures. Despite these natural protections, human activities continue to pose a threat to the Great Wall. The biocrusts only cover about two-thirds of the studied sections, and their effectiveness depends on local conditions. While the study offers promising insights into conservation, it also underscores the need for careful management to ensure the long-term preservation of this ancient structure.