is described in the Berkeley philosophy forum.
The notion of earth can be brought out in more detail when one contrasts it with sky, as Heidegger does. Heidegger almost never rattles off the four -earth, sky, divinities, mortals- merely in a list, but almost always puts things in pairs “earth and sky, divinities and mortals”. These two pairs are meant to be understood as productively oppositional in some sense. So let’s clarify sky, and see how the opposition between earth and sky might work. Sky, again, has a literal and metaphorical aspect. Literally, Heidegger’s “sky” embraces the physical sky as well as the natural phenomenon and objects (weather, clouds the stars, etc.) that go along with it. Metaphorically speaking, the sky again recalls the notions of concealment and unconcealment. The sky is a source of “glow” but also a source of “gloom.” It reveals our world, and at the same time conceals it with the darkness of night. If the earth is a spatial horizon, the sky might be considered our temporal one: the weather, years, seasons, all suggest time and temporal elements. Both earth and sky, both literally and as spatio-temporal horizons, show up in our practices. We plan our lives and projects in accordance with what the earth allows and with what time allots.