Trillions of metallic nodules on the sea floor could help stop global heating, but mining them may damage ocean ecology

In a display cabinet in the recently opened Our Broken Planet exhibition in London’s Natural History Museum, curators have placed a small nugget of dark material covered with faint indentations. The blackened lump could easily be mistaken for coal. Its true nature is much more intriguing, however.

The nugget is a polymetallic nodule and oceanographers have discovered trillions of them litter Earth’s ocean floors. Each is rich in manganese, nickel, cobalt and copper, some of the most important ingredients for making the electric cars, wind turbines and solar panels that we need to replace the carbon-emitting lorries, power plants and factories now wrecking our climate.