Incan Empire Aided by Global Warming

July 28, 2009 -- A 400-year warm spell helped the ancient Inca to build the largest empire ever to exist in the Americas, a new study has established.

Beginning around 1100 A.D., the increase in temperature served as a "perfect incubator" for the Inca's expansion, an international team of researchers report in the current issue of the journal Climate of the Past.

"Climate warming does not always have to be a negative issue. Our research shows that it can favor societal development, " lead author Alex Chepstow-Lusty, a palaeoecologist from the French Institute for Andean Studies in Lima, Peru, told Discovery News.

The Inca ruled the largest empire on Earth -- stretching from the present-day southern border of Colombia to central Chile -- by the time their last emperor, Atahualpa, was executed by Spanish conquistadors in 1533.

Because the Inca language has no written form -- it has long been considered the only major Bronze Age civilization without a written language -- and due to the destruction of their heritage by the Spanish, the details of their meteoric rise have remained a mystery.

WATCH VIDEO: Find out how Spanish conquistadors vanquished one nation within the Inca empire: the Chachapoyas.

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Now, Chepstow-Lusty and colleagues at universities in France, the United Kingdom and the United States have found reliable witnesses to recount the most important times of the Inca empire: pollen and seeds buried in layers of mud on the floor of Lake Marcacocha in the Cuzco region of the Peruvian Andes.

Similar to the rings in the trunk of a tree, each layer of sediment represents a fixed period of time. In the case of Lake Marcacocha, the researchers were able to analyze a 1,200-year-old sediment record.

"This record reveals a period of sustained aridity that began from A.D. 880, followed by increased warming from A.D. 1100 that lasted beyond the arrival of the Spanish in A.D. 1532," the researchers wrote.

Pollen, seeds and other environmental indicators in the layers of mud showed that the Inca recast the landscape with agricultural terraces supplied by canals fed by glacial melt water during the warmer weather .

Trees were also moved up the mountains. "(Trees) were used sustainably to protect against erosion and increase soil fertility. These practices allowed major agricultural production," Chepstow-Lusty said.

According to the researcher, the resultant surplus of maize and potatoes freed up a large part of the population to build a large army as well as a huge road network and grand structures, including Machu Picchu.