- Francisca Santana-Sagredo & Julia Lee-Thorp & Rick Schulting
- The Conversation*
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2 hours
Image source, Thomas Janisch/Getty Images
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Atacama is the driest place on earth, except for some Antarctic valleys.
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The Atacama Desert, in the north of Chile, is one of the driest places on the planet; for years it receives no rain.
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For farming communities to survive and prosper, they would need water and nutrients from the soil, both in short supply.
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However, people lived in the Atacama long before modern technology existed.
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The water shortage was addressed using oasis water and complex irrigation systems. For soil nutrients, the solution they found, centuries before the arrival of the Incas around 1450, was to bring a super fertilizer from the coast in the form of seabird droppings or “guano”.
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It was the key finding of our new research, in which we analyzed the remains of 246 crops and wild plants found at 14 archaeological sites in the Atacama.
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These plants cover a period of almost 3,000 years spanning several ancient civilizations, followed by the Incas and finally the period of European colonization until 1800.
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Image source, Víctor Suárez Naranjo / Getty Images
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Sea cliffs in Chile covered in guano.
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The “massive impact” … of bird droppings
One way to tell if guano was used to fertilize these ancient plants is to look up the proportions of the nitrogen isotopes (15N / 14N) in the remains of the plant.
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These two isotopes (atoms of the same chemical element) differ only in atomic mass, but they behave a little differently in natural systems and can therefore act as tracers of natural biochemical processes.
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We know that even small amounts of seabird guano fertilizer have a massive impact on nitrogen isotope ratios in modern corn, raising them well above what is possible, either naturally or with any other fertilizer.
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Image source, JeremyRichards/getty Images
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Seabirds off the coast of Chile … and guano.
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When we look at the remains of archaeological crops, such as corn, squash, and chili peppers, we find similarly high isotope ratios in plants dating from around 1000 AD onward.
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The proportions of nitrogen isotopes found in human skeletons of the region, well preserved in arid conditions, also they changed drastically next to crops.
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Scientists had previously thought that this showed that people had eaten fish from the sea.
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Marine fish are known to have high ratios of nitrogen isotopes, especially those found off the coast of Chile, thanks to the very cold, nutrient-rich waters of the Humboldt Current (a cold, coastal Pacific ocean current Oriental).
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Our research found that people in ancient Atacama communities got those high nitrogen isotope values from fish, only indirectly, through the seabirds, who ate the fish and then they excreted it as guano, which became fertilizer for crops.
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Image source, Hoberman Collection/Getty Images
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Guano helped the civilizations that inhabited the arid Atacama Desert survive.
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The guano inequality
Our research also found that not everyone seems to have had access to this super fertilizer.
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While there were indications that high nitrogen isotope ratios increased markedly in corn kernels from 1000 AD onward, indicating a considerable increase in crop yield and allowing for larger settlements, some kernels lacked this. evidence.
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Rather they showed signs of other fertilizers as green manure or manure from llamas and their relatives.
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Skeletons from the same cemeteries dating from the same period also showed dramatic differences in their nitrogen isotope ratios, suggesting that access to fertilized crops was not evenly distributed in the community.
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It could be that some families or clans had privileged links with the coast (about 90 km away) and could obtain guano from seabirds and use it mainly for their own benefit as a source of power and prestige.
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The desert flourished, but for some more than for others.
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Image source, Hans Neleman/Getty Images
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Research indicates that guano distribution was uneven.
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“White gold”
The fertilization of guano continued in the Inca and colonial periods.
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At the beginning of the 19th century, it became better known around the world as a super fertilizer and became an important source of income for Peru (of which Atacama was then part).
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Hundreds of thousands of tons were shipped abroad each year, mainly to the United States and Western Europe; It was at this time that guano became known as “White gold”.
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The importance of guano was eclipsed soon after, first by a new resource from the Atacama Desert, salitre (sodium nitrate), which was extensively mined, and then by the introduction of cheaper synthetic fertilizers in the early 1900s.
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Guano fertilizer has experienced a resurgence through its use in organic agriculture, but in Chile it is now prohibited extract fresh guano, and both the guano and the seabirds that produce it are protected by law.
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Francisca Santana-Sagredo is an adjunct professor at the Universidad Católica de Chile. Julia Lee-Thorp is Emeritus Professor of Archaeological Science, and Rick Schulting is Professor of Scientific and Prehistoric Archeology. They both work at the University of Oxford, UK.
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This note originally appeared on The Conversation and is published here under a Creative Commons license. You can read here the original article.
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