Sharing the Ocean's Wealth At their current rate of usage, known reserves of many key transition metals will be depleted in less than 50 years. Other sources must be found. One promising source is nodules strewn over large portions of the ocean floor. Varying from a few millimeters to a few meters in diameter, these chunks consist mainly of manganes and iron oxides, with oxides of other elements present in smaller amounts. Billions of tons exist, but mining them presents major technical and political challenges. Global agreements have designated the ocean floor as international property, so cooperation will be required to mine the nodules and share the mineral rewards.