Deep sea mining is the extraction of minerals from the seabed of the deep sea. The main ores of commercial interest are polymetallic nodules, which are found at depths of 4–6 km (2.5–3.7 mi) primarily on the abyssal plain. The Clarion–Clipperton zone (CCZ) alone contains over 21 billion metric tons of these nodules, with minerals such as copper, nickel, cobalt and manganese making up roughly 30% of their weight. It is estimated that the global ocean floor holds more than 120 million tons of cobalt, five times the amount found in terrestrial reserves.