Partly because of these arguments, many ecologists have thought that the uplands—more than 90 percent of the Amazon basin—must consist of untouched primary forest and savannah, a landscape never painted by the human brush. The geoglyphs suggest something else. Because they cannot be seen through thick forest, researchers believe they must have been constructed at a time when the region had little tree cover. In other words, the great forests of the western Amazon may have looked considerably different in the not too distant past.
