Although nearly 40 years have passed since Brazil banned slash-and-burn practices in its Atlantic Forest, the destruction lingers. New research reveals that charred plant material is leaching out of the soil and into rivers, eventually making its way to the ocean. So much of this “black carbon” is entering the marine ecosystem that it could be hurting ocean life, although further tests will be needed to confirm this possibility.

People have used fire to shape Earth’s vegetation for millennia. In Brazil’s Atlantic Forest, Europeans began burning trees to make way for settlements and agriculture in the 16th century. What once blanketed 1.3 million square kilometers and ranked as one of the world’s largest tropical forests had shrunk to 8% of its former size by 1973, when protective laws were put in place.