The Great Wall’s Ancient Secret: How Microbes Retain a Wonder of the World Standing
The Great Wall of China, a UNESCO World Heritage site and one of the New7Wonders of the World, stretches over 21,000 kilometers. Built as a defensive fortification, its construction began as early as the 7th century. But how has this monumental structure endured for millennia, weathering countless environmental challenges?
The Power of ‘Biocrusts’
Recent scientific analysis reveals a surprising answer: a significant portion of the Great Wall’s enduring strength comes from microscopic organisms. These organisms, known as ‘biocrusts,’ form a thin layer on organic materials and play a crucial role in protecting the wall from erosion.
Rammed Earth and Microbial Synergy
Researchers discovered that the wall’s builders frequently employed rammed earth – a construction technique involving compacted mixtures of soil, gravel and organic materials. Even as seemingly vulnerable to erosion, this method inadvertently fostered the growth of biocrusts.
What Makes Up a Biocrust?
These protective layers are composed primarily of cyanobacteria, microorganisms capable of photosynthesis, and various types of moss. These organisms work together to reinforce the wall’s structure.
“The ancient builders intuitively understood which materials would create a more stable structure,” explains Bo Xiao, a professor of soil science at the Chinese Academy of Agricultural Sciences in Beijing, and a co-author of the study.
Strengthening the Foundation: Ancient Techniques
Builders also utilized clay, sand, and binding agents like lime, layering them onto the walls to enhance their strength. This combination of materials and techniques proved remarkably effective over centuries.
Scientific Evidence: A Comparative Analysis
Researchers collected samples from eight different sections of the Great Wall, constructed between 1368 and 1644 during the Ming Dynasty. They found that 67% of the samples contained biocrusts.
Using portable mechanical instruments, they measured the mechanical strength and soil stability of the samples, comparing them to barren soil. The results were striking: samples containing biocrusts were sometimes up to three times stronger.
How Biocrusts Bind and Strengthen
The strength stems from the organisms within the biocrusts. Cyanobacteria and other life forms release substances, such as polymers, that bind soil particles together. This creates a natural “cement,” significantly enhancing the structural stability of the wall.
“Here’s because cyanobacteria and other forms of life within the biocrust excrete substances, such as polymers, that bind particles together, helping to strengthen the structural stability by creating what is essentially a cement,” Xiao explains.
Future Implications for Sustainable Construction
The discovery of biocrusts’ role in the Great Wall’s preservation offers valuable insights for modern sustainable construction. Mimicking this natural process could lead to the development of eco-friendly building materials and techniques.
Could Biocrusts Revolutionize Building Practices?
Researchers are exploring the potential of incorporating biocrust-forming organisms into soil stabilization projects and the creation of bio-cement. This could reduce reliance on traditional, energy-intensive cement production, lowering the carbon footprint of the construction industry.
FAQ
Q: What are biocrusts?
A: Biocrusts are thin layers of living organisms – primarily cyanobacteria and moss – that form on soil surfaces and help stabilize the ground.
Q: How ancient is the Great Wall of China?
A: Construction began as early as the 7th century BC, with significant building occurring during the Ming Dynasty (1368-1644).
Q: What materials were used to build the Great Wall?
A: Rammed earth (a mixture of soil, gravel, and organic materials), clay, sand, and lime were commonly used.
Q: Can biocrusts be used in modern construction?
A: Research is ongoing to explore the potential of using biocrust-forming organisms in soil stabilization and bio-cement production.
Did you know? The Great Wall isn’t a single, continuous structure. It’s a series of fortifications built over centuries by different dynasties.
Want to learn more about ancient engineering marvels? Explore our articles on Roman aqueducts and Inca stonework.
Share your thoughts! What other ancient building techniques do you find fascinating? Leave a comment below.
