Scientists have discovered that metallic nodules on the seafloor produce their own oxygen in the dark depths of the Pacific Ocean. These polymetallic nodules, generating electricity like AA batteries, challenge the belief that only photosynthetic organisms create oxygen, potentially altering our understanding of how life began on Earth. In the total darkness of the depths of the Pacific Ocean, scientists have discovered oxygen being produced not by living organisms but by strange potato-shaped metallic lumps that give off almost as much electricity as AA batteries. The surprise finding has many potential implications and could even require rethinking how life first began on Earth, the researchers behind a new study said on Monday. It had been thought that only living things such as plants and algae were capable of producing oxygen via photosynthesis — which requires sunlight. But four kilometres (2.5 miles) below the surface of the Pacific Ocean, where no sunlight can reach, small mineral deposits called polymetallic nodules have been recorded making so-called dark oxygen for the first time. The discovery was made in the Clarion-Clipperton Zone (CCZ), an abyssal plain stretching between Hawaii and Mexico, where mining companies have plans to start harvesting the nodules. The lumpy nodules — often called “batteries in a rock” — are rich in metals such as cobalt, nickel, copper and manganese, which are all used in batteries, smartphones, wind turbines and solar panels. The international team of scientists sent a small vessel to the floor of the CCZ aiming to find out how mining could impact the strange and little understood animals living where no light can reach.