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24-Aug-2005
Last Edited
A long dry period punctuated by three intense droughts
probably played a major role in the mysterious collapse of Mayan
civilisation in Mexico, according to a new study.
The severe droughts, each lasting between three and nine years, may have
the been the final straws for a civilisation already on the verge of
collapse, says a report published today in the journal
Science.
"Between about 750 and 950 AD, the Maya experienced a demographic
disaster as profound as any other in human history," said the report, by
an international research team led by Dr Gerald Haug of the
Swiss Federal Institute of
Technology in Zürich.
The Mayan were so successful that at their so-called Classic Maya peak,
around 750 AD, the civilisation supported a population of between three
and 13 million people, the researchers said. But then it progressively
collapsed and by the early 9th century, many of its cities and towns had
been permanently abandoned.
The study details new evidence that the three droughts occurred around
810, 860, and 910 AD - corresponding to the three phases of Mayan
collapse suggested by archaeological evidence.
The researchers also found that a more subtle but long-term drying trend
was ongoing during the collapse. The droughts may have been what
specifically "pushed Mayan society over the edge," they said.
The findings are based on an analysis of long-term climate records as
revealed in pristine undisturbed sediments from the Cariaco Basin, off
northern Venezuela. The distinctly layered sediments, washed out from
land by rivers, show up as pairs of light and dark bands that correspond
to annual wet and dry seasons.
Within them, the team identified yearly variations in titanium levels,
which reflect the amount of rainfall each year. They correlate well with
palaeoclimate data obtained elsewhere from sources such as ice cores and
tree rings.
Until now, however, climate records from the time had not been precise
enough to test the relationship between drought and the Maya's downfall
during the 9th and 10th centuries, the report said.
The Mayans began cultivating maize in the region about 2000 BC, using
dryland farming techniques that depended on fallowing to rest the soil
and needed relatively little labour. Like other Native Americans, they
went on to develop sophisticated ways of intensively cultivating fertile
soils associated with seasonal and permanent wetlands, on which multiple
crops could be grown year after year.
Living in the Yucatan lowlands of Mexico and depending mainly on an
inconsistent rainfall cycle, the Maya developed labour-intense networks
of raised fields as well as canals, reservoirs and other systems for
storing and gravity-powered distribution of rainwater.
The Mayans had abandoned their major cities once before - between about
150 and 250 AD - an incident that may also be due to drought. But their
population constantly recovered, cities were reoccupied and their
culture blossomed.
"The control of artificial water reservoirs by Maya rulers may also have
played a role in both the florescence and the collapse of Maya
civilisation," the researchers wrote.
Other scientists have suggested that drought may have undermined the
institution of Mayan ruling class when existing ceremonies and
technologies failed to provide sufficient water.
The Mayans were an ancient people whose high civilisation flourished in
what is today Mexico, Honduras and Guatemala. They created monuments as
impressive as those in ancient Egypt, were proficient in mathematics and
astronomy and invented a unique written language.
Bob Beale - ABC Science
Online
More Info?
Sun
cycle may have affected the Maya, News in Science 23 May 2001
El Nino
cycles ancient and peaking, News in Science 20 Nov 2002
[This is the print version of story
http://www.abc.net.au/science/news/stories/s807089.htm]
Intense droughts blamed for Mayan collapse 13.03.03
The Mayan civilisation of Central America collapsed following a series of intense droughts, suggests the most detailed climatic study to date.
The sophisticated society of the Maya centred on large cities on the Yucatán peninsula, now part of Mexico. Their population peaked at 15 million in the 8th century, but the civilisation largely collapsed during the 9th century for reasons that have remained unclear to this day.
Now, researchers studying sediment cores drilled from the Cariaco Basin, off northern Venezuela, have identified three periods of intense drought that occurred at 810, 860 and 910AD. These dates correspond to the three phases of Mayan collapse, the scientists say.
Furthermore, the entire 9th century suffered below average rainfall, "so it was a dry period with three intense droughts", says Gerald Haug, from ETH in Zurich, Switzerland, who led the research. "The climate change must have been what pushed the Mayan society over the edge."
Experts on the Maya have greeted the new data cautiously. "Any explanation for decline is a complex one: over-population, environmental problems and economic factors all made them vulnerable," says Jeremy Sabloff, director of the Museum of Archaeology and Anthropology at the University of Pennsylvania. "But there is growing evidence that climate played a role. Perhaps it was the straw that broke the camel's back."
Wet and dry
Haug and his colleagues identified the bands in the sediment cores that correspond to the annual wet and dry seasons. They then analysed the concentration of titanium in the sediment in great detail, taking measurements at intervals of 50 micrometres.
Titanium is an indicator of rainfall, explains Haug, because higher precipitation washes more of the metal from the land into the ocean floor sediments. The difference in concentration between the wet and dry season each year is as much as 30 per cent.
"We looked in detail at the period corresponding to 9thand 10thcenturies - taking 6000 measurements per 30 centimetres of sediment - and found three extreme minima, as well as a low background level of that lasted about 100 years," Haug told New Scientist.
Latest and greatest
But archaeologist Norman Hammond, at Boston University, is unconvinced that drought caused the downfall of the Maya. He notes that the northern Yucatán city of Chichén Itzá was not abandoned until the 13th century "Why did the latest and greatest fluorescence of the Mayan series occur in the area that we know to be the driest," he asks.
The Maya certainly had hydraulic expertise, Jeremy Sabloff points out, building canals, viaducts and reservoirs. Moreover, they had experienced and survived droughts before.
"The Maya thrived for 1500 years before these droughts, so it's clearly not climate alone that brought down the southern cities of the Yucatán peninsular," he says.
Journal reference: Science (vol 299, p 1731)
