We've created some three part cards about thermal vents.
Many large, unusual creatures live deep underwater by the hydrothermal vents, fissures where hot water comes out of the earth. The water varies in temperature from very cold to very hot. There is not any sunlight and most organisms get their energy from the hydrogen and hydrogen-sulfide that is vented by volcanic activity. These nutrients, as well as other chemicals and boiling hot water, shoot into the ocean as geysers. The ones that provide the most nutrients are called black smokers.
The various types of "smokers" and warm water come from volcanic activity underneath the ocean floor, where water is superheated before being emitted in geysers.
The process of getting energy from these chemicals is known as chemosynthesis, which is done mostly by archaea and bacteria.
Because of the lack of sunlight, this ecosystem is alien-like in someways. Some people think that life elsewhere in the solar system or the universe may get energy from chemicals instead of sunlight.