The world's oceans cover more than seventy per cent of the Earth's surface, (0) YET we know remarkably little about what lies beneath the waves. Scientists estimate that over eighty per cent of the ocean floor remains unexplored, making it one of the 1 understood environments on the planet. Deep-sea exploration is extraordinarily difficult, not least because of the extreme pressure and total darkness found 2 great depths. Sending crewed submarines to the ocean floor is both dangerous and expensive, which is 3 much of the research in this field is now carried out using remotely operated vehicles. These robotic craft are capable of reaching depths that would be impossible 4 humans to survive, and they can collect samples and capture images of species never before seen. Despite the challenges, the discoveries made so 5 have been remarkable. Hydrothermal vents — openings in the seabed that release superheated water — were only found in the late 1970s, and the ecosystems that surround them continue to fascinate researchers. Understanding these environments is not just a matter of scientific curiosity 6 also of practical importance, particularly in the fields of medicine and biotechnology. New compounds derived 7 deep-sea organisms are already being tested for use in treating diseases. The more we learn about the ocean, the more 8 becomes clear that its potential is far greater than we ever imagined.