Fig. 1.

Biogeochemical modelled atmospheric [CO₂] over the past 500 million years (Berner 2006, 2009). Letters indicate major events in plant evolutionary history. a Origination of vascular plants (Harrison and Morris 2018); b origination of stomata (Edwards et al. 1998; Duckett et al. 2009); c development of the planate leaf (Beerling et al. 2001); d origination of conifers (Leslie et al. 2018); e origination of cycads and ginkgoales (Tralau 1968; Pant 1987; Shen et al. 2005); f origination of angiosperms (Dilcher 2000; Soltis et al. 2008); g origination of C3 grasses/occurrence of phytoliths (Prasad et al. 2005; Strömberg 2011), and h origination of C4 grasses (Sage et al. 2012)