The oxygen-free muck at the bottom of ponds, swamps and oceans hosts invisible microbes that run the planet's carbon, nitrogen, phosphorus and sulfur cycles, and quietly archive its past climates.
Ponds, swamps, estuaries, the sea floor: the same stuff is lying there. It is goopy, it stinks, and in an earthquake it can slide downhill in one piece.
The deeper you go, the less oxygen, and the better business gets
Mud is clay, silt, water and a little organic matter. It is saturated, so oxygen runs out fast, and further down there is none at all.
That anoxic layer is where the planet's busiest workers live: bacteria that do not need oxygen. Marine benthic ecologist Stephen S. Hale runs through their output — breaking dead organic matter back into nutrients plants can use, driving the global cycles of carbon, nitrogen, phosphorus and sulfur, and turning fertiliser nitrate into harmless nitrogen gas.
Mud is also a ledger that goes back millions of years
Almost nothing large can live in mud, worms and clams aside. That turns out to help: sediment piles up layer by layer, undisturbed, and old climates stay sealed inside it.
Mudflats, mangroves and salt marshes also absorb waves and hold shorelines against erosion. Praise of mud, Hale writes, begets the defence of mud.
People have used it for millennia: the first writing was pressed into clay tablets, and there are pots, bricks, wall coatings, face masks, clay pills for diarrhoea — and, of course, play.
No mud, no dinner. And no mud fights either.
Why it matters
The costliest page of climate policy is rarely about cutting emissions; it is about where carbon is stored. The silt under lakes and seas is a long-term savings account, and disturb the account and the carbon goes back into the air.
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