The Bible says we're made of clay (Adam is Hebrew for red clay). That may be because it is perhaps the most common and widespread substance on earth, but some scientists also hypothesize that life actually originated in a "soup" of clay, water, organic compounds, and energy from light or lightning. In addition, the crystalline structure of clays exhibit a logic of coding similar to DNA, the building block of life. And of all earthly phenomena, only two require water for their existence: clay, and life. It is estimated that all the clay on the planet, evenly spread out, would make a layer a mile thick - which is not surprising, given that clay is decomposed rock.
What distinguishes clay from other dirt is particle size, as well as molecular and chemical properties. Size is. very important: a grain of coarse sand falls through four inches of water in one second, a grain of silt takes five minutes, and a single grain of very fine clay can take up to 860 years! Clay is so slow partly because of shape as well as size - particles are thin and flat. Indeed, a single gram of clay can have a surface area larger than a football field. That flatness helps make clay plastic - flat surfaces make it easy for particles to stick, like two wet sheets of paper. In addition to size and shape, however, clay particles are also electrically charged, which means that they have a tremendous capacity to attract and adhere to clay or other molecules (including water). All these properties make clay the wonderful, magical substance that it is.
RESOURCE William Bryant Logan assembled these facts in a marvelous book of essays titled, Dirt, The Ecstatic Skin of the Earth.