There are multiple theories as to what caused the collapse of the Classic Maya civilization, such as invasion, war, environmental degradation, etc. In the 1990s, however, researchers were able to piece together climate records for the period of the Maya collapse, and found that it correlated with an extreme drought. Now, a team of scientists from the Universities of Florida and Cambridge has developed a method to measure the different isotopes of water trapped in gypsum, a mineral that forms during times of drought when the water level is lowered. Based on these measurements, the team found that annual precipitation decreased between 41% and 54% during the period of the Maya civilization’s collapse, with periods of up to 70% rainfall reduction during peak drought conditions, and that relative humidity declined by 2% to 7% compared to today.
The fall of the ancient Maya is a commonly used example of how abrupt past changes in climate have contributed to the decline of ancient societies.
While paleoclimate studies from the region indicate that the Maya collapse occurred during an exceptionally dry period, it has not been clear just how dry that period actually was.
Most climate data are limited to qualitative reconstructions — a period being simply wetter or drier than another, for example.
“The role of climate change in the collapse of the Classic Maya civilization is somewhat controversial, partly because previous records are limited to qualitative reconstructions, for example whether conditions were wetter or drier,” said study lead author Nick Evans, a PhD student in the Department of Earth Sciences at the University of Cambridge.
“Our study represents a substantial advance as it provides statistically robust estimates of rainfall and humidity levels during the Maya downfall.”
In the study, Evans and co-authors reconstructed the isotopic composition of water from Lake Chichancanab, Mexico, using sediment cores containing precipitated gypsum.
They measured the triple oxygen and hydrogen isotope compositions of water molecules incorporated in the crystalline structure of gypsum deposited as layers on the lake bottom, as a proxy for past aridity.
They found that during the Terminal Classic Period (800-1000 CE), annual rainfall in the Maya lowlands was reduced by nearly 50% on average, and up to 70% during peak drought conditions.
Also, for the first time, the researchers were able to measure a 3-8% decline in relative humidity compared to today.
The results, published in the journal Science, reveal the severity and duration of the drought experienced by Lowland Maya society and provide the quantitative data necessary to better understand its impact on Maya agricultural and sociopolitical systems.
Nicholas P. Evans et al. 2018. Quantification of drought during the collapse of the classic Maya civilization. Science 361 (6401): 498-501; doi: 10.1126/science.aas9871
Source link: https://www.sci.news/archaeology/enormous-drought-maya-civilizations-collapse-06285.html