The Rise of Trees and How They Changed Paleozoic Atmospheric CO2, Climate, and Geology

Abstract

Large vascular plants with deep, extensive root systems arose and spread over the continents starting about 380 million years ago during the Devonian Period. Previously there were only bryophytes, algae, and small vascular plants restricted to the edges of water courses (Gensel and Edwards 2001). Large plants are important because their vast root systems produce a larger interface between the geosphere and the biosphere than do the more primitive species, where the plant/mineral interface is greatly reduced. This large interface allows plants to take up nutrients more rapidly, to grow bigger and faster (Algeo and Scheckler 1998), and to accelerate mineral weathering (Berner 1998). In addition , the larger plants, upon death, supply a much greater mass of organic matter for burial in sediments. Because of these effects, the rise of large vascular plants brought about a dramatic change in the level of atmospheric CO 2 , the climate, and the formation of carbon-rich deposits (coal) during the late Paleo-zoic. 1.2 Plants, Weathering, and CO 2 The level of CO 2 is controlled, on a long-term, multimillion-year timescale, by two carbon cycles: the silicate-carbonate cycle and the organic matter cycle. The