Matthew Lachniet, an associate professor at UNLV, looks at rock
formations in a cave in the Sierra Madre region of Mexico during a June
2011 trip. Lachniet says cave rock accurately records rainfall patterns
through the centuries. His research might help explain the rise and fall
of Mesoamerican civilizations.
Across the sweep of a thousand years, as ancient cities bloomed and
died in southern Mexico, the water in Juxtlahuaca Cave went drip, drip,
drip.
Now a UNLV researcher is using a stalagmite built by those
droplets to chart 2,500 years of rainfall and draw new links between
human history and climate change.
The findings by professor
Matthew Lachniet and his research team could help shed light on Nevada's
climate over the past several thousand years and offer clues to how it
might change in decades to come.
"We have a saying in geoscience:
The past is the key to the future," said Lachniet, a geologist and
climate scientist at the University of Nevada, Las Vegas.
Scientists have only recently begun to unlock the secrets of cave formations as "ancient rain gauges," he said.
Outside
of tree rings, stalagmites offer one of the most accurate climate
records known to science because they tend to grow at a uniform rate and
collect traces of naturally occurring uranium.
And since they are
formed by minerals in water droplets that crystallize and accumulate
over the course of thousands of years, stalagmites can offer a much
longer record than tree rings.
Lachniet and company were able to
pinpoint the age of various layers in the stalagmite from Juxtlahuaca to
within about 10 years. They could then track rainfall amounts over time
by analyzing carbon dioxide trapped in those layers.
What
researchers discovered was a period of above average rainfall between
the first and third centuries that coincided with the rise of the
largest early Mesoamerican city of Teotihuacan, near present day Mexico
City.
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