Scientists are using space satellites to unravel
one of the great mysteries of the ancient Mayan Empire.
by Patrick L Barry
Where the rain forests
of Guatemala now stand, a great civilization once flourished. The
people of Mayan society built vast cities, ornate temples, and towering
pyramids. At its peak around 900 A.D., the population numbered 500
people per square mile in rural areas, and more than 2,000 people
per square mile in the cities - comparable to modern Los Angeles
This vibrant "Classic
Period" of Mayan civilization thrived for six centuries. Then,
for some reason, it collapsed.
The fall of the Maya
has long been one of the great mysteries of the ancient world. But
it's more than a historical curiosity. Within sight of the Mayan
ruins, in the Petén region of Guatemala near the border with
Mexico, the population is growing again, and rain forest is being
cut to make farmland.
"By learning what
the Maya did right and what they did wrong, maybe we can help local
people find sustainable ways to farm the land while stopping short
of the excesses that doomed the Maya," says Tom Sever at the
Marshall Space Flight Center (MSFC).
Photo copyright Tom Sever.
ruins in Guatemala
Sever, NASA's only
archeologist, has been using satellites to examine Mayan ruins.
Combining those data with conventional down-in-the-dirt archeological
findings, Sever and others have managed to piece together much of
From pollen trapped
in ancient layers of lake sediment, scientists have learned that
around 1,200 years ago, just before the civilization's collapse,
tree pollen disappeared almost completely and was replaced by the
pollen of weeds. In other words, the region became almost completely
Without trees, erosion
would have worsened, carrying away fertile topsoil. The changing
groundcover would have boosted the temperature of the region by
as much as 6 degrees, according to computer simulations by NASA
climate scientist Bob Oglesby, a colleague of Sever at the MSFC.
Those warmer temperatures would have dried out the land, making
it even less suitable for raising crops.
would have also disrupted rainfall patterns, says Oglesby. During
the dry season in the Petén, water is scarce, and the groundwater
is too deep (500+ feet) to tap with wells. Dying of thirst is a
real threat. The Maya must have relied on rainwater saved in reservoirs
to survive, so a disruption in rainfall could have had terrible
(Changes in cloud formation
and rainfall are occurring over deforested parts of Central America
today, studies show. Is history repeating itself?)
Using classic archeology
techniques, researchers find that human bones from the last decades
before the civilization's collapse show signs of severe malnutrition.
Photographed by Daniel Irwin
agriculture in Petén, Guatemala
used to argue about whether the downfall of the Maya was due to
drought or warfare or disease, or a number of other possibilities
such as political instability," Sever says. "Now we think
that all these things played a role, but that they were only symptoms.
The root cause was a chronic food and water shortage, due to some
combination of natural drought and deforestation by humans."
Today, the rain forest
is again falling under the axe. About half of the original forest
has been destroyed in the last 40 years, cut down by farmers practicing
"slash and burn" agriculture: a section of forest is cut
down and burned to expose soil for planting crops. It's the ash
that gives the soil its fertility, so within 3-5 years the soil
becomes exhausted, forcing the farmer to move on and cut down a
new section. This cycle repeats endlessly ... or until the forest
is gone. By 2020, only 2% to 16% of the original rain forest will
remain if current rates of destruction continue.
It seems that modern
people are repeating some of the Maya's mistakes. But Sever thinks
disaster can be averted if researchers can figure out what the Mayans
did right. How did they thrive for so many centuries? An important
clue comes from space:
Sever and co-worker
Dan Irwin have been looking at satellite photos and, in them, Sever
spotted signs of ancient drainage and irrigation canals in swamp-like
areas near the Mayan ruins. Today's residents make little use of
these low-lying swamps (which they call "bajos,"
the Spanish word for "lowlands"), and archeologists had
long assumed that the Maya hadn't used them either. During the rainy
season from June to December, the bajos are too muddy,
and in the dry season they're parched. Neither condition is good
Sever suspects that
these ancient canals were part of a system devised by the Maya to
manage water in the bajos so that they could farm this
land. The bajos make up 40% of the landscape; tapping into
this vast land area for agriculture would have given the Maya a
much larger and more stable food supply. They could have farmed
the highlands during the wet season and the low-lying bajos
during the dry season. And they could have farmed the bajos
year after year, instead of slashing and burning new sections of
Image courtesy NASA/MSFC
satellite image revealing linear features that may have
been Mayan irrigation canals
Could today's Petén
farmers take a lesson from the Maya and sow their seeds in the bajos?
It's an intriguing
idea. Sever and his colleagues are exploring that possibility with
the Guatemalan Ministry of Agriculture. They're working with Pat
Culbert of the University of Arizona and Vilma Fialko of Guatemala's
Instituto de Antropología e Historia to identify areas in
the bajos with suitable soil. And they're considering planting
test crops of corn in those areas, with irrigation and drainage
canals inspired by the Maya.
A message from 900
A.D.: it's never too late to learn from your ancestors.