LONDON - A new research on Peruvian lake sediments has suggested that the meteoric rise of the Incan empire between 1400 and 1532 was driven by a sustained period of warmer weather.

According to a report in New Scientist, the sediments, from a core going back 4000 years, contain biological and organic evidence revealing sharp changes in land use and agriculture around Marcacocha, a small lake near Cuzco at the heart of the ancient empire.

The higher temperatures, starting around 1150, ended thousands of years of cold aridity, and enabled Incan farmers to build mountainside terraces for growing crops at altitudes previously too cold to support agriculture.

The extra warmth, lasting around 400 years, also supplied extra water for irrigation in the shape of melt-water from Andean glaciers at higher altitudes.

Fed by bountiful surpluses of maize and potatoes, Incans were free to engage in other activities such as establishing huge networks of roads.

Most importantly, the surpluses enabled them to build fit and well-resourced armies and weaponry.

From 1400 onwards, they rapidly conquered territory stretching southward 4000 kilometres, from what is now Ecuador to midway through Chile.

The empire met an abrupt demise in 1533 when the invading Spanish armies arrived.

But, the rapid expansion of Incan power until then has remained unexplained, ascribed most often to superior social organisation and technology.

It seems that climate played an important part, according to Alex Chepstow-Lusty of the University of Montpellier in France, and head of the team analyzing the cores.

“All this would have been impossible without the increase in temperature,” he said.

For the first 3000 years or so represented within the 8-metre section of lake sediments, the climate was relatively cold, with the core contents dominated by rock and sandy fragments washed into the lake from the mountains.

Then, sediments from 800 AD were marked by evidence of an arid period including a drought lasting about 100 years, shown mainly by the appearance of sedge seeds that are normally found only at the fringes of the lake.

Around 1100, came the lift in temperatures that gave the Incans such a boost.

Cores from this date onward show evidence of a sudden surge in Incan agriculture that included wholesale re-landscaping of the terrain around the lake.

“By 1100, a threshold was reached which enabled Incans to start scaling the mountains, re-landscaping the slopes and putting in terrace systems for agriculture, but also, there was more meltwater from the glacier feeding new irrigation systems,” said Chepstow-Lusty. (ANI)