“ 7 cubic miles (11 km^3)”
They think the conversion factor between cubic miles and cubic km is the same as between miles and km? Hm ....
They think the conversion factor between cubic miles and cubic km is the same as between miles and km? Hm ....
They underestimated the volume of olivine rock about 3 times, which means that its mining would cost about 15% of the overall cost of mining of fossil fuels, assuming current prices of olivine rock and crude oil. This is a very rough estimate that doesn't take into account several factors, most importantly economy of scale.