The process is called ‘enhanced rock weathering’. Here’s how it works. Farmers spread a crushed volcanic rock called basalt onto their fields. Rain absorbs CO2 from the atmosphere as it falls. It reacts with the volcanic dust to form carbonates. That is, minerals that lock in carbon. These minerals help farmers by replenishing depleted soils. Eventually they are washed into the sea, where they reduce ocean acidification, a consequence of excess CO2 in the atmosphere that can harm marine life.