These volcanic features occur on the mid-ocean ridge, a worldwide undersea system of ridges that forms a mountain chain more than 60,000 kilometres in length. The water that spews from the vents is hot and rich in minerals - notably sulphides. When it hits the cold ocean water, the minerals precipitate from the solution and form what looks like black smoke. Some of these minerals crystallise around the vents and increase its size, whilst others seep into the ocean floor. The sulphur-bearing minerals that seep from the Earth's crust form the basis of a food chain.
Bacteria surround the vent and create an energy source for all the other creatures in the ecosystem.
Professor Jacquie McGlade explains . This site chronicles the adventures of the Museum's scientists, engineers, and educators as they collected a sulphur chimney from the ocean floor. This site is about ocean research. The third programme The Ocean Planet airs on the 6th September 9.00pm on Radio 4 .