Cobalt is a trace element in the Earth system yet plays an important role in life, being the metal center of vitamin B12, which is crucial to various methyltransferase enzymes. However, there are few rock-forming minerals that incorporate cobalt into their structure, and these are typically found in mafic minerals that are rare in modern silicic continents. Moore et al.  explore the early Earth and find that the weathering rates of the relatively mafic “continents” of the Archean were greater than that of modern silicic continents, and along with low marine sulfur concentrations, were sufficient to keep cobalt bioavailable as a mechanism for carbon fixation and the development of early life.
More modern, non-cobalt based pathways such as photosynthesis may have evolved in response to reduction in cobalt availability. Would these modern processes upon which modern life depends have been possible without the early forms enabled by cobalt and other bioavailable trace metals provided by enhanced Archean mafic weathering? How did the coevolution of rocks and organisms control the development of modern oceans, continents, and life on Earth? These and related questions will need to be further explored in additional studies that build on our emerging understanding of the interacting roles of Archean lithospheric composition, ocean chemistry, and trace elements in the development and evolution of early life.
Citation: Moore, E. K., Hao, J., Prabhu, A., Zhong, H., Jelen, B. I., Meyer, M., Hazen, R. M. & Falkowski, P. G. . Geological and Chemical Factors that Impacted the Biological Utilization of Cobalt in the Archean Eon. Journal of Geophysical Research: Biogeosciences, 123. https://doi.org/10.1002/2017JG004067
—Dork Sahagian, Associate Editor, JGR: Biogeosciences