The secret that keeps the Great Wall standing has been found
Large surfaces of Great Wall of China are held together thanks to a "biocrust", thin layers of organic materials that have helped protect the architectural wonder from erosion. A research team made the discovery while analyzing sections of the Great Wall of China, which stretches more than 21.000 kilometers and was built over several centuries, starting in 221 BC, as a way to protect the Chinese empire. from external enemies.
During construction, ancient workers often used a type of "inoculated" soil that included a mixture of organic materials such as soil and gravel pressed together. While these materials may be more susceptible to erosion than other materials, such as solid stones, they often help promote the growth of materials that researchers refer to as living stucco, or "biocrust." This living stucco consists of cyanobacteria (microorganisms that are capable of photosynthesis), mosses and lichens that help strengthen the construction, especially in arid and semi-arid regions of the country according to the study that published in the journal "Science Advances".
“The ancient builders knew which materials could make the structure more stable. To enhance mechanical strength, the soil of the wall was always made with clay, sand and other binders such as lime by the original builders. These components provide fertile ground for the organisms that create 'biocrusts', says Bo Xiao, a professor of soil science at the College of Soil Science and Technology, China Agricultural University, who led the research team.
To test the strength and integrity of the Great Wall, researchers collected samples in eight different sections built between 1368 AD. and 1644 AD during the Ming Dynasty. They found that 67% of the samples contained "biocrustaceans" which the researchers call "ecosystem engineers".
The researchers studied the mechanical strength and soil stability of the samples and compared this data to wall sections containing bare soil. They found that the "biocrust" samples were in many cases three times stronger than her plain soil samples. "This is because cyanobacteria and other forms lifes into the biocrust they secreted substances, such as polymers, that bound tightly to the earth particles helping to strengthen their structural stability by creating what was essentially cement. These cementitious substances, the biological neyes and the soil aggregates within the biocrust layer eventually form a cohesive network with strong mechanical strength and stability against external erosion," explains Xiao.