Frost's research started with a hypothesis that in ancient times, rocks could have pulled carbon dioxide from the oceans. Then, as the rocks were drawn down into the mantle, high pressures force the CO2 to leave the rocks. Once the CO2 was free, iron in the mantle stripped it of its oxygen. That left just the naked carbon, which was squished into diamond by the high heat and temperatures. That was the hypothesis anyway, "[a]nd that is exactly what Frost found when he recreated the process using his presses – essentially forging a diamond from thin air," writes Robson.