The Amazon isn't as pristine as you might think. Turns out, humans have been changing its landscape for thousands of years.

This suggests that some of the Amazon we know today was largely influenced by ancient human activity — and one of the latest pieces of evidence that support this idea comes from mysterious designs in the Brazilian state Acre.

Hundreds of these man-made designs popped up in the 1980s, but archaeologists still aren't sure what purpose they served. But, a new study, published in the Proceedings of the National Academy of Sciences, revealed that samples collected at a few of the sites contained evidence of charcoal — a byproduct of fire.

Most likely, ancient humans were setting fires in the Amazon as an early form of deforestation.

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