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Our transcription: Consider, for example, calcium and phosphorous, two of the essential elements in bone. Calcium is abundant throughout nature, but animals obtain phosphorous primarily by eating plants which absorb the phosphorous from the soil in which they grow. The most important original source of the phosphate in soils is the relatively rare mineral, apatite. The apatite in a chunk of granite the size of a fist would probably fit onto the head of a pin. But when granite is weathered into soil, the tiny apatite grains decompose releasing soluble phosphate, which is subsequently taken up by plants. And then through the food chain, by people. Apatite is found in many varieties of rocks, though usually only in minute traces. Still, it is the major source of all the phosphates so vital to life. If it were not released by the weathering, no vertebrate land animals could exist.
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