Prevent aging and hide its effects. Human beings have tried for centuries and with various techniques, from the application of powders and plasters to surgery, to combat the inevitable, what is inherent to a living being. Well, the same thing happens with monuments. A group of scientists has identified an effective biological organism that prevents one of the seven wonders of the world, the Great Wall of China, from suffering marks on its stones from the passage of centuries due to erosion.
The Great Wall is an incredible fortification about 21,000 kilometers long that began to be built in the 5th century BC. C. and was completed in the 16th century AD. The Chinese Empire built it as a defensive barrier against the invasions of the Xiongnu people who inhabited Manchulia and Mongolia. Although only 30% is preserved, the work had branches to stop the enemies. Its height ranged between four and seven meters.
One of the most visited parts of the monument, declared a World Heritage Site in 1987 by UNESCO, is that of the Ming dynasty (1368-1644). This section of the wall has been the subject of a recent study by researchers from the Academy of Sciences and the Chinese Agricultural University who have been interested in its erosion.
The surprise is that the sections, despite being built with compacted earth, have not suffered the logical destruction that affects most monuments. The experts determined that 67% of the work is covered by the so-called biocrusts.
These are crusts formed by cyanobacteria that in the arid areas of the wall have a blue photosynthetic pigment and in the semi-arid or humid regions they are formed by mosses of the Pottiaceae family, according to the Chinese news agency Xinhua.
Better with mosses
The scientists determined that the biocrusts covered by moss improve the “mechanical resistance” of the wall and the stability of the soil between 37 and 178% compared to other sections of rammed earth blocks without the natural crust. Apparently, biocrusts “serve as stabilizers, as 'sacrificial' layers and drainage roofs” against the action of external agents such as rain, wind or temperature changes, according to Xiao Bo, one of the authors of the study.
The conclusions are promising for conserving heritage, but for the moment it will not be possible to see other of the seven monuments chosen by popular vote in 2001 as declared wonders of the world (Chichén Itzá, Petra, the Colosseum, Taj Mahal, Christ the Redeemer or the ruins of Machu Picchu). Nor does it seem to be the solution to the stone problems suffered by such outstanding monuments as cathedrals and other historical buildings.
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