In science and philosophy earth (German Erde, Greek ge) can refer to one in a set of primordial material elements (earth, air, fire, and water, for the Greeks; wood, fire, earth, metal, water, for the Chinese) and to the physical body on which humankind lives. As physical home, the Earth serves as the reflective horizon or framework for human self-awareness and as a contingent unity among the array of individual entities they encounter. The Earth, defined by an elemental earthiness of rock and soil, is that which grounds the identity of humans in both physical and psychological senses, independent of wherever they may venture in information networks or outer space, while serving as a fund of resources available for exploitation. The tensions between these various approaches are imaged in the diagrammatic icon of the atom and the photo of the blue planet taken from space: matter that is...