  The magnitude of the biotic enhancement of weathering (BEW) has profound
implications for the long-term carbon cycle. The BEW ratio is defined as how
much faster the silicate weathering carbon sink is under biotic conditions than
under abiotic conditions at the same atmospheric pCO2 level and surface
temperature. Thus, a 13th hypothesis should be considered in addition to the 12
outlined by Brantley...(2011) regarding the geobiology of weathering: The BEW
factor and its evolution over geological time can be inferred from
meta-analysis of empirical and theoretical weathering studies. Estimates of the
global magnitude of the BEW are presented, drawing from lab, field, watershed
data and models of the long-term carbon cycle, with values ranging from one to
two orders of magnitude.
