There are many ways in which human activities now compete with or exceed comparable natural processes on the planet. The nitrogen cycle (Vitousek et at, 1997) is perhaps the most obvious, but there are others, such as erosion, where ploughs, in particular, play a spectacular role; we may not move the sediment all the way to the sea, but we move more of it, and from different places, than nature does (Wilkinson and McElroy, 2007). Whether we break up more limestone than natural processes do, I couldn’t say. But we do do it a lot, and we do do it spectacularly. I’d love to see this series by Naoya Hatakeyama in the C-print-on-aluminium flesh.
According to Pink Tentacle Japan alone produces 200m tnnes of calcium carbonate a year from its quarries, so I’d guess world figures might be on the order of a billion tonnes. If I had to hazard a further guess I would guess that the situation for limestone is the opposite of the situation for soil. There, as I understand it, agriculture moves more than nature, but doesn’t move it very far. For limestone I would guess that more falls off mountain sides unaided than is blow away by quarriers, but that the stuff that’s quarried travels further, quicker. It takes times for boulders to wander.
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