Thanks for the great question.

All living things convert energy in their environment into a form that the organism uses to grow and survive. Living things called heterotrophs (like all animals) do this by consuming other organisms to obtain energy. Autotrophs, on the other hand, can directly transform energy from non-biological sources, for instance when plants convert sunlight into chemical energy through photosynthesis.

In 1977, new types of autotrophs were discovered living around hydrothermal vents at the bottom of the ocean. These organisms, including the giant tube worm, convert energy from chemicals produced by these volcanic hot spots through a process called chemosynthesis. This process allows these organisms to use chemicals like sulfur or hydrogen to create sugars and amino acids, or the energy and materials that build up their bodies. Chemosynthesis therefore allows organisms to live in places that were previously thought to impossible for life.

The ability of these organisms to use chemicals instead of sunlight for energy radically changed our understanding of how and where life can thrive. In fact, scientists have now proposed that life on worlds other than Earth, for instance Mars or Jupiter’s moon Europa, may use chemosynthesis to exist without energy from the sun.

Chemosynthesis is the creation of sugars from carbon dioxide and water without the need of sunlight. Many organisms live in environments that don't have sunlight, and so chemosynthesis is their only source of energy.

Also, chemosynthesis is a necessary step in the cycling of many elements that other organisms need to live and grow. For example, ammonia is poisonous to plants and animals; plants can't get the nitrogen out of ammonia that they need to make proteins. However, there are bacteria that combine with ammonia with oxygen in the atmosphere to make nitrates, which plants can use, and the bacteria get the energy they need to live as well. Similar cycles exist for phosphorous and sulfur.