Six Materials — Sand, salt, iron, copper, oil, lithium

Almost every manufactured object traces back to a short list: sand for glass and chips, salt for chemicals, iron for steel, copper for wiring, oil for plastics, lithium for batteries. Digging and refining them takes a large share of the world's energy. The digital economy rests on a very physical floor.

• Making a tonne of steel or a single silicon wafer takes an amount of heat and processing that no amount of software can argue away.
• A small number of trading houses move much of this material between countries. They rarely own the mines, rarely make the news, and set prices that everybody else pays.