Figure 1From: Ordovician ash geochemistry and the establishment of land plantsIntensity of volcanic activity through the Phanerozoic. Activity represented by relative changes in volcanic arc volume [17], and frequency of ash bed deposition [18]. Ordovician peak in intensity is coincident with earliest records of plants [11, 12], and decline in atmospheric CO2 (RCO2 is concentration compared to present atmosphere: [1]). Consequence is a shift of biomass from subsurface to surface. True roots are known from the Siluro-Devonian, but an earlier soil anchoring system is possible [52].Back to article page