Archeologists reveal why the Great Wall of China has remained preserved for over 2,000 years

The Great Wall of China, a symbol of ancient civilization, stretches across the northern borders, standing as a testament to over two millennia of history. Despite its grandeur, what remains today is only a fraction of its former self, as time and natural forces have taken their toll on the structure.

However, a recent discovery reveals that nature itself might be playing a crucial role in preserving this historical wonder. Thin layers of bacteria, moss, lichen, and other organisms, known as biocrusts, have been found to protect sections of the Great Wall, shielding it from wind, rain, and other corrosive elements.

A study published in Science Advances highlights the significant role these "living skins" play in conserving this ancient architectural marvel. With advances in technology and research, scientists are now exploring the potential of cultivating new biocrusts to prevent further degradation of the Wall.

Nichole Barger, an ecologist at the Nature Conservancy, praised the study as "innovative and creative," noting that the protective effects of biocrusts have gained increasing recognition in recent years. These biological layers are well-known for stabilizing dryland ecosystems and preventing soil erosion.

While the more famous sections of the Great Wall are constructed from stone or brick, other parts were built using compacted soil, or rammed earth. Over time, this material deteriorates due to various factors like rainwater infiltration, wind erosion, salt crystal formation, and temperature fluctuations.

Yet, the same compacted soils can also host biocrusts, which cover about 12% of the Earth's land surface, particularly in arid regions like northern China. These biocrusts vary in form, ranging from thin bacterial networks a few millimeters thick to thicker layers of moss and lichen several centimeters high.

Soil scientist Bo Xiao from the China Agricultural University, along with his colleagues, conducted a study to investigate the role of biocrusts in preserving the Great Wall. Their research revealed that biocrusts, primarily composed of moss or cyanobacteria, covered more than two-thirds of the Wall’s surface in the areas they examined. By comparing the physical properties of biocrust-covered rammed earth with those of bare, biocrust-free soil, they made a significant discovery.

The study found that biocrust-covered rammed earth was less porous and exhibited higher shear strength and compressive strength compared to uncovered sections. These properties help protect the Wall from degradation by reducing wind erosion, preventing water and salt infiltration, and enhancing the overall stability of the rammed earth.

Thicker biocrusts dominated by moss provided more protection than thinner ones dominated by cyanobacteria. Bettina Weber, an ecologist at the University of Graz, commended the study for exploring whether biocrusts' protective effects could extend to cultural heritage sites, suggesting their findings could pave the way for integrating biocrust research into various scientific fields.

Interestingly, this study challenges the common belief in heritage conservation that plant growth is harmful to buildings or archaeological sites. Matthew Bowker, the study’s author and an ecologist at Northern Arizona University, explained that the fear of plant growth primarily stems from potential damage caused by root systems, which biocrusts do not have.

However, despite their protective capabilities, biocrusts face their own threats. Recent studies have warned that climate change and intensive land use could cause many biocrusts to vanish, taking their protective benefits with them. This loss could have severe consequences for the Great Wall, especially with rising temperatures favoring thinner cyanobacterial crusts that require less water.

Efforts to restore damaged or depleted biocrusts are still in the research and development phase. Labs worldwide are exploring the possibility of stimulating biocrust regrowth, but understanding the timeframes required for different types to flourish in various climates and disturbance levels remains a challenge. Estimates for biocrust recovery range from years to centuries.

Nichole Barger suggested that intentionally cultivating biocrusts along a relatively small feature like the Great Wall could be more manageable than attempting to restore biocrusts across vast landscapes. Given the Great Wall's significance as "a cultural symbol of China and Chinese civilization," as noted by Bo Xiao, finding effective ways to preserve this site for future generations is imperative.

As researchers delve deeper into the protective potential of these tiny organisms, the Great Wall of China may continue to stand not only as a testament to ancient engineering but also to the resilience of nature’s unlikely protectors.

Note: Materials provided above by The Brighter Side of News. Content may be edited for style and length.

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