Maya Civilization Done In By Brightening Of The Sun
The Maya were talented astronomers, religiously intense in their
observations of the sun, moon and planets. Now, new research shows
something in the heavens may have influenced their culture and
ultimately helped bring about their demise.In an article in today's issue of the journal Science,
a team of researchers led by a University of Florida geologist reports
finding that the Yucatan Peninsula, seat of the ancient Maya
civilization, was buffeted by recurrent droughts. More
importantly, the research shows, the droughts -- one of which is
thought to have contributed to the collapse of the Maya civilization --
appear to have been caused by a cyclical brightening of the sun. "It
looks like changes in the sun's energy output are having a direct
effect on the climate of the Yucatan and causing the recurrence of
drought, which is in turn influencing the Maya evolution," said David
Hodell, a UF professor of geology and the paper's lead author. In 1995, Hodell and two colleagues at UF published results in the journal Nature
suggesting that the ninth-century collapse of the Maya civilization may
have been influenced by a severe drought that lasted for more than 150
years. The paper,
co-authored by Mark Brenner, a UF assistant professor of geology and
director of UF's Land Use and Environmental Change Institute, and Jason
Curtis, a UF geology researcher, was based on analysis of a sediment
"core" from Lake Chichancanab on the north central Yucatan Peninsula in
Mexico. Cores are samples of
lake sediment retrieved by driving a hollow tube into the lake bottom.
The sediments are deposited layer by layer, like a wedding cake, with
the oldest layer at the bottom. Such cores provide a timeline that
allows researchers to obtain a continuous record of changes in climate,
vegetation and land use. For
the latest research, Hodell, Brenner and Curtis returned to the lake
and collected a new series of cores. The researchers discovered layers
of calcium sulfate, or gypsum, concentrated at certain levels in the
cores. Lake Chichancanab's
water is nearly saturated with gypsum. During dry periods, lake water
evaporates and the gypsum falls to the lake bottom. The layers
therefore represent drought episodes. The researchers found the
recurrence of the deposits is remarkably cyclical, occurring every 208
years, although they varied in intensity. The 208-year
cycle caught the researchers' attention because it is nearly identical
to a known 206-year cycle in solar intensity, Hodell said. As part of
that cycle, the sun is most intense every 206 years, something that can
be tracked through measuring the production of certain radioactive
substances such as carbon-14. The
researchers found the drought episodes occurred during the most intense
part of the sun's cycle. Not only that, the researchers found the
droughts occurred at times when archeological evidence reflects
downturns in the Maya culture, including the 900 A.D. collapse. Such evidence includes abandonment of cities or slowing of building and carving activity. As
Hodell said, the energy received by the Earth at the peak of the solar
cycle increases less than one-tenth of 1 percent, so it's likely that
some mechanism in the climate is amplifying the impact in the Yucatan. Archaeologists
know the Maya were capable of precisely measuring the movements of the
sun, moon and planets, including Venus. Hodell said he is unaware,
however, of any evidence the Maya knew about the bicentenary cycle that
ultimately may have played a role in their downfall. "It's
ironic that a culture so obsessed with keeping track of celestial
movements may have met their demise because of a 206-year cycle," he
said. The cycle continues to
the present, which happens to fall into about the middle of the
206-year period, Hodell said. Even a severe drought today, however,
isn't likely to have the same impact on the culture as in ancient
times. Brenner noted North Korea currently is suffering an extreme
drought, but the country has the benefit of international aid. "Nobody
stepped in to help the Maya out," he said, "and as conditions worsened,
it probably created a lot of stress among various Maya cities competing
for resources." Thomas
Guilderson of the Lawrence Livermore National Laboratory assisted the
UF scientists in the research, which was funded by the National Science
Foundation Paleoclimate Program. The cores were collected for a BBC
program on climate and Maya culture collapse. - By Aaron Hoover
[Contact: David Hodell, Mark Brenner, Aaron Hoover ]
17-May-2001 |