Figure 3.

(a) CO₂, (b) O₂ and (c) numbers of described species of lycopsids through time. Note that arborescent lycopsids were diverse only in the high O₂, low CO₂ atmosphere of the Carboniferous and Permian. In (a), CO₂ values are given as RCO₂; relative enrichment over modern (preindustrial) level. Redrawn from figures in Berner (2006), Bergman et al. (2004), Berner & Kothavala (2001) and Nikas et al. (1985). The curves in (c) are traced compilations of several figures and therefore represent approximate rather than exact values.