Mysterious geoglyphs can teach us about the Amazon's past—and its worrisome future

We know that the forests of the Amazon have a long history of human interference. Scientists have been studying the region's ancient geoglyphs—large designs traced into the ground with rocks and other debris—since the 1960s, when deforestation by cattle ranchers first revealed the stunning shapes. Because the geoglyphs only appeared once forests had burned away, it follows that the ancient artists must have burned their own trees to the ground to build them.