For centuries, the mystery of the Maya civilization?s rise and fall has captivated explorers and scholars. In one of the first accounts of the region, the American explorer John Lloyd Stephens wrote: ?Here were the remains of a cultivated, polished, and peculiar people, who had passed through all the stages incident to the rise and fall of nations; reached their golden age, and perished, entirely unknown.?
?To us,? he continued in an 1841 travel journal, ?it was all a mystery.?
Now, with the help of modern science, part of that mystery is being put to rest. A new analysis of 2,000-year-old stalagmites suggests the role that climate change played in both the Maya civilization?s achievements and in its undoing.
?How do you get so many different centers that are so successful?? said Douglas J. Kennett, a geoarchaeologist at Penn State University and co-author of a new paper in the journal Science, referring to the range of Maya sites. ?We think climate played a role in that development, and we also think climate played a role in how that all came apart at the seams.?
Previous research in the region by other scholars has supported the notion that drought was responsible for the Maya?s collapse. Some arrived at this conclusion by examining tree rings, while others studied lake sediment deposits or marine records. But the dating and locations were not closely aligned enough with the ancient Maya to be considered definitive.
?These were wonderful studies, but there were some limitations,? Dr. Kennett said. ?Archaeologists were reluctant to accept them because of uncertainties in the record.?
In a larger study of the region?s climate, Dr. Kennett and his colleagues discovered that some of the stalagmites from a field site in Yok Balum cave in Belize yielded high-resolution oxygen isotopes related to the rainwater that entered cave deposits.
Although researchers often use oxygen isotopes to understand precipitation in past eras, the stalagmites? exceptional quality allowed the team to collect two samples per year over a 2,000-year period. That yielded a robust continuous record of wet and dry events, with fewer potential errors than earlier studies.
Dr. Kennett and his colleagues compared their results with written records of the Maya civilization ? for example, on well-dated stone monuments that celebrated rulers and depicted wars. From these social and climactic records, a chronology of the Maya?s rise and fall emerged.
Around A.D. 440, the records indicate, anomalously high rainfall allowed the Maya to embark on an unprecedented expansion across across modern-day Mexico and northern Central America. During this so-called Classic Period, generations of kings and their queens ruled around 70 interconnected but autonomous cities, some of which supported up to 70,000 citizens.
In Guatemala?s famed Tikal settlement, the Maya built a series of complex water collection and diversion systems, as my colleague Kelly Slivka noted here recently. Water supported crops, which in turn supported a flourishing, culturally rich civilization.
By 640, however, ?it was clear that these city centers were running into trouble, which we think was related to decreased agricultural productivity,? Dr. Kennett said.
Rainfall began to wane and crops withered, probably because of natural changes in the Intertropical Convergence Zone, or the area where the northeast and southeast trade winds come together.
As the Late Classic Period unfolded over the next three centuries, warfare raged unchecked and some of the state centers disintegrated. When kings lost control, people began to disperse, and by 900, only a handful of the once-thriving centers remained occupied.
When an extreme 100-year drought hit the region in 1000, most of the Maya had long since departed from their ruined cities, which depended heavily on the climatic conditions that once favored their creation.
Of course, climate was not the sole factor leading to the civilization?s collapse. But Dr. Kennett and his colleagues believe that it helped to set off the political unrest and exodus that eventually led to the Maya?s undoing.
?Climate matters in terms of development of complex societies like the ones we live in today, ? Dr. Kennett said. ?The unique climate conditions that set up the Maya?s social and political systems also lured them into a very vulnerable situation.?
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