The twilight zone: Every night trillions of tiny creatures rise from the ocean depths. During World War Two sonar technicians made an extraordinary discovery. The pings from their echo sounders reflected off what they thought must be the ocean floor. But the sea was much shallower than they had expected and – even more puzzlingly – the seabed seemed to move up and down throughout the day. https://www.bbc.com/future/article/20260706-the-deep-sea-creatures-that-rise-every-night #globalmuseum #OceanLife #oceans #marineanimals