Fig. 4. O2 consumption vs extents of ultramafic rocks.
Potentials for consuming more than 2 (a) or 3 (b) Tmole O2 yr−1 as functions of the extent of Fe-bearing rocks exposed in either continents or seafloor (in km2). Scales at the bottom compare given values to present-day continents and seafloor extents. Results are from models assuming serpentinization rate = 10-6 km yr−1. Light and dark grey shaded areas depict estimated ranges in the extent of ultramafic rocks exposed in continents 3.0 and 2.5 Ga ago, respectively. Vertical dashed grey lines depict maximum extent of ultramafic or komatiite exposures at 3.0 Ga based on compositional estimates of Greber et al.53 and continental growth models of (A) Armstrong63, (D) Dhuime et al.56, and (T) Taylor and McLennan65. Other continental growth models64,66 yields much lower maximum ultramafic extents. The blue shaded area represents the extent of oceanic plateaus at the present-day (~4–6% of the seafloor)71. Curves of various colors depict the results of models simulating rocks belonging to different compositional groups as indicated by the MgO contents.