Geologists tell us that we live in the Anthropocene, the period marked by humanity's global transformation of the environment (1). More than half of Earth's terrestrial surface is now plowed, pastured, fertilized, irrigated, drained, fumigated, bulldozed, compacted, eroded, reconstructed, manured, mined, logged, or converted to new uses. These activities have long-lasting effects on life-sustaining processes of the near-surface environment, recently termed Earth's “critical zone” (2). The full range of Anthropocene changes in Earth's critical zone is not well quantified, especially belowground (see the figure) (3–6), where observed changes justify a major expansion in monitoring to better ensure the sustainability of crop and soil productivity, and the functioning of the global atmosphere and hydrosphere (3).
Richter, Daniel deB., Jr., and Mobley, Megan L. (2009): Monitoring Earth's Critical Zone. Science 326(5956): 1067-1068. DOI: 10.1126/science.1179117