The Mayan city-states could have disappeared not only due to prolonged droughts, but also due to massive deforestation and soil degradation, geologists say in an article published in the journal Nature Geoscience.
“Today, these parts of the jungle look like a real primeval forest. But if you look at their soil, you can understand that ecosystems in the distant past experienced a sharp collapse and never fully recovered,”says Peter Douglas of McGill University in Montreal, Canada.
The mysteries of the Yucatan
The Mayan civilization lasted several millennia, leaving behind many "dead cities" and cultural monuments in the Yucatan Peninsula, disappearing from the face of the earth around the ninth century AD, when most of the Mayan city-states were abandoned by their inhabitants. The reasons for this civilizational collapse are still the subject of controversy among scientists.
One of the possible reasons for the collapse of this civilization, according to a number of archaeologists today, could be droughts caused by climate change and overpopulation of Mayan cities. The first serious confirmation of this theory was found in 2012 during excavations in the territory of Tikal, one of the largest cities of the Indians, where scientists have discovered a complex system of reservoirs and canals, indicating the importance of water in the lives of its inhabitants.
Subsequent excavations in other Mayan city states have yielded more conflicting results. They showed that the collapse of their culture could be associated not only with the climate, but also with political conflicts between the Indian "policies". This led scientists to argue about the place the climate occupied in their lives.
Douglas and his colleagues uncovered another factor that influenced this "geopolitical catastrophe" by analyzing how the soils in those tropical forests where the Mayan cities were located, during the heyday and decline of their civilization.
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To do this, scientists went to the jungle in southern Mexico and northern Guatemala, and extracted from the bottom of three lakes - Chikankanab, Salpeten and Itzan - soil samples that have been forming over the past four thousand years.
As geologists explain, every year new deposits of silt appear there, containing small portions of pollen and other plant remains that fall there along with the wind. In addition to the relatively “fresh” traces of flora, there are some waxy molecules of much older origin in the soil of the lake bottom.
The age of these molecules, according to Douglas, serves as a kind of indicator of the amount of organic matter that enters and is washed out of the soil. If there are a lot of plant and animal remains, then the microbes "eat" more accessible compounds and do not touch this wax, because of which its age will be much higher than the rest of the traces of flora life. If the soil becomes poorer, then these molecules will not be much older than the "normal" biomass.
Ecology invisible hand
With this in mind, Douglas's team measured the age of the wax and other deposits using radiocarbon analysis. As it turned out, before the emergence of city-states, about 3500 years ago, wax was about 1.5 thousand years older than the rest of the organic deposits. This, as scientists note, corresponds to the typical values for modern tropical jungle, untouched by man.
Around 1500 BC, the situation changes dramatically. The differences in the age of the wax and "normal" biomass began to disappear sharply, reaching the mark of 380-400 years. At the same time, as scientists note, Mayan villages begin to turn into the first large city-states.
Soil depletion, according to geologists, is due to the fact that the Maya massively cut down the jungle and cleared them for planting corn and other crops. The jungle soil, as indicated by deposits from the bottom of the lakes, did not have time to recover and quickly lost fertility. This, most likely, forced the Indians to make new clearings and abandon old fields.
How does this relate to the collapse of their civilization? The fact is that the soils did not recover even after the Mayans left the deforested areas of the forest. The amount of organic matter in it, judging by the absence of changes in the composition of the fossil soil, remained low even centuries after the “exploiters” left.
The reason for this, as scientists suggest, was that the destruction of the forest sharply accelerated the erosion of the soil, including the leaching of some trace elements from it. As a result, the acid-base balance changed, which accelerated the decomposition of organic matter by microbes and depleted the soil.
Such irreversible changes, which influenced the yield of Maya fields, according to scientists, were one of the main reasons for the collapse of their civilization, whose effect stretched out for several centuries, if not millennia.