We sit with MInus Materials, founded by Wil Srubar and Sarah Williams out of the LIving Materials Laboratory at University of Colorado Boulder. There is a type of algae that grows a shell made of calcium carbonate, which is what is used as cement for concrete, a dirty industry that emits about 8% of the world's total carbon emissions. With Minus, just replacing the calcium carbonate (limestone) inputs alone reduces the emissions by 60%. But stacked with other technologies, we can make completely carbon negative concrete at a competitive cost.