Amazonian Rain Forest Less Than 2,000 Years Old

From the Daily Mail:

Huge areas of the Amazon rainforest were grassland until just 2,000 years ago, it has been revealed.. [sic]

Researchers say the find sheds new light on the Amazon's history - and show it was a savannah rather than the high forest it is today. 

They believe much of the area was grassland until a natural shift to a wetter climate about 2,000 years ago let the rainforests form, according to a study that challenges common belief that the world’s biggest tropical forest is far older. 

The arrival of European diseases after Columbus crossed the Atlantic in 1492 may also have hastened the growth of forests by killing indigenous people farming the region, the scientists wrote in the U.S. journal Proceedings of the National Academy of Sciences (PNAS). 

'The dominant ecosystem was more like a savannah than the rainforest we see today,' John Carson, lead author at the University of Reading in England, said of the findings about the southern Amazon. 

The scientists said that a shift toward wetter conditions, perhaps caused by natural shifts in the Earth’s orbit around the sun, led to growth of more trees starting about 2,000 years ago. 

The scientists studied man-made earthworks, uncovered by recent logging in Bolivia, that included ditches up to about a kilometer (1,100 yards) long and up to 3 meters deep and 4 meters wide. 

They found large amounts of grass pollen in ancient sediments of nearby lakes, suggesting the region had been covered by savannah.  

They also found evidence of plantings of maize, pointing to farming. 

The Amazon has traditionally been seen as a pristine, dense rainforest, populated by hunter-gatherers.  

In recent years, however, archaeologists have found hints that indigenous peoples lived in the thick forest, but managed to clear tracts of land for farming. 

The PNAS study suggests a new idea – that the forest simply did not exist in some regions.

Actually, it is more than just rudimentary agriculture.  Charles C. Mann's book, 1491, describes archaeological evidence of advanced cultures and large population centers in the pre-Colombian Amazon basin.