Granites aged 1.9 Ga to 1.5 Ga exhibit molybdenite mineralization globally. Sandstones deposited during the mid-Proterozoic have a provenance dominated by 1.9 to 1.7 Ga basement. The mid-Proterozoic surface environment was, consequently, receiving detritus from the molybdenum-rich granites. Thus there was a supply of molybdenum available in terrestrial or shallow marine environments at a time when molybdenum was required to support the evolution of multicellular life.
Parnell, J., & Lindgren, P. (2016). Anomalous supply of bioessential molybdenum in mid-Proterozoic surface environments. Precambrian Research, 275, 100-104. https://doi.org/10.1016/j.precamres.2015.12.016