A new study has been released that challenges common belief that the world's largest tropical forest is older than 2,000 years.
There is a good chance that swathes of the Amazon may have been grassland until a natural shift to a wetter climate about 2,000 years ago let the rainforests form, according to the study, which was published in the U.S. journal Proceedings of the National Academy of Sciences (PNAS).
European diseases that arrived in the U.S. after Columbus crossed the Atlantic in 1492 might have also hastened the growth of forests by killing indigenous people farming the region.
"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.
More trees starting growing around 2,000 years ago, most likely because of natural shifts in the Earth's orbit around the sun.
For the study, the scientists analyzed man-made earthworks, discovered during recent logging in Bolivia, which included ditches up to approximately 1,100 yards long and up to 3 meters deep and 4 meters wide, according to the study.
It was there that they found large amounts of grass pollen in ancient sediments of nearby lakes. This suggests that the location had been covered by savannah.
In the past, the Amazon has been viewed as a pristine, dense rainforest occupied by hunter-gatherers. More recently, however, archaeologists have discovered clues that indigenous people lived in the forest, and figured out how to clear tracts of land for farming.
The PNAS study suggests a new theory: that the forest did not exist in some regions.
The researchers "findings suggest that rather than being rainforest hunter-gatherers, or large-scale forest clearers, the people of the Amazon from 2,500 to 500 years ago were farmers," the University of Reading said in a statement, according to Reuters.
Carson suggests that a fifth of the Amazon basin, in the south, could have been savannah until the shift.
Getting a better understanding of the forest could help solve a number of mysteries about climate change, according to the study.
The Amazon rainforest affects climate change a great deal because trees soak up heat-trapping carbon dioxide as they grow. They then release it when they rot or are burnt, according to the study.
Brazil has slowed down deforestation rates recently.
Carson said that the growth of Amazonian forests could have contributed to the Little Ice Age, which took place from about 1350 to 1850, by absorbing heat-trapping gases from the air.
"These indigenous systems were highly sophisticated. There are over 80 domesticated or semi-domesticated crops in the Amazon," said Michael Heckenberger, an expert on the Amazon at the University of Florida, according to Reuters. "In Europe at the time they were working with about six."
See Now: OnePlus 6: How Different Will It Be From OnePlus 5?