fusain

— By the Carboniferous period 300 million years ago, trees had spread over so much of the globe and locked down so much carbon that they altered the atmosphere completely. Levels of oxygen went rocketing up from 15 percent to 35 percent, with a correspondingly massive impact on life on earth. Animals became gigantic, plants struggled to adapt, and oxygen became so available that fire destroyed huge swathes of trees. A particular type of fossil carbon called fusain is everywhere in Carboniferous fossil deposits, evidence of widespread forest fires. But through their structure and chemistry, trees learned to survive and even to master fire, as well as the other elements, and out of the ashes of the Carboniferous forests a thousand new types of tree evolved.