Cam_Figure_7

Published 09/08/2012 | Full size is 600 × 378 pixels

Figure 7 — Model showing how the biosphere revolution from Ediacaran (at left) to Cambrian times and later (at right) shifted the position of important geochemical boundaries in the sediment and hence the quality of fossil preservation (after Brasier et al. 2010). In the Ediacaran period, high levels of minerals could build up near the sediment–water interface, so sediment turned to rock quickly and often entombed remains before organisms could decay. The numbered metabolic processes are: (1) oxygenic photosynthesis; (2) calcium carbonate precipitation; (3) &aerobic respiration, including metazoans; (4) calcium carbonate dissolution; (5) calcium phosphate &precipitation; (6) &anaerobic respiration by sulphate-reducing bacteria; (7) anaerobic respiration by &methanogenic bacteria.

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