Figure 4. Proposed narrative for the cyanobacterial context of Earth’s oxidation. Relative probability density distributions are shown for crown bacteria (purple), total group Cyanobacteria (red) and crown group Cyanobacteria (blue). This hypothesized history of cyanobacteria shows oxygenic forms arising from within a diversity of anoxygenic stem groups in the Archean. IAP Origins of Life Seminar Series Poster The Fournier lab hiking in New Hampshire’s White Mountains.