|P.1082 right column bottom paragraph: "New tools for palaeoecological analyses have also helped reveal the antiquity of fires and of flammable ecosystems. Carbon isotopes from soil organic matter can reveal the history of forest versus grassland in the tropics because of the distinct isotope signals of C3 (forest) versus C4 (grass) photosynthetic pathways. Isotopic analyses of soil organic matter show that tropical forests often replaced ancient fire-prone grasslands when, if fires were of recent human origin, you would expect the reverse. Wildfires cause distinctive changes in the structure of plant cell walls so that charcoalified fossils can be identified unequivocally. The charcoal content of coal also records ancient fires in mires. Analyses of charcoalified plant fossils and charcoal content of coal have revealed that fires have been burning plants for more than 400million years (Ma). Fire activity has waxed and waned over geological time peaking during periods of high atmospheric oxygen such as the Carboniferous (360–350 Ma) and the Permian (300–251 Ma). During the Cretaceous (140–65 Ma), when angiosperms first spread to dominate lowlatitude vegetation, fires were common. Their legacy can be seen in fossil Cretaceous flowers preserved in fine detail as ancient charcoal. Ancient fire activity has also been traced from studies of charcoal taken from cores drilled in the ocean floor. In the North Pacific, e.g., charcoal fluxes have revealed an exponential increase in vegetation fires from 10 Ma, coincident with the spread of tropical grasslands and savannahs."