A large shark tooth, at least five centimeters (two inches) long, rests on a bed of potential polymetallic nodules explored during Dive 06 of the 2026 Cook Islands ROV Exploration cruise. Polymetallic nodules form when iron and manganese minerals slowly build up, or accrete around a small object, like a shark tooth or grain of sand. They can take millions of years to grow to the size we see here.