The oldest forms of life on the Earth, Archaeobacteria are a diverse group of single-celled bacteria that gave rise to the Eubacteria.  Metabolically they are anaerobic (carrying out metabolic processes in the absence of oxygen) and derive their energy from various processes: 1) anaerobic photosynthesis, which works by converting sulfur compounds (e.g. hydrogen sulfides) to elemental sulfur to get the needed hydrogen; and extracting carbon dioxide from sea water to get the carbon, all of this powered by sunlight; 2) by converting carbon dioxide to methane, or 3) by sulfate respiration (converting sulfates to hydrogen sulfides).

They have left virtually no fossil record, except for Carbon and Sulfur traces enriched in light isotopes (¹²C vs ¹³C and ³²S vs ³⁴S). Still, they are the first life on earth, and may have evolved near black smokers,in association with plate tectonics.

This is a photo of a black smoker. They occur in mid-ocean rifts, where ocanic water circulates throught the faulted ocean floor and comes in contact with magmatic materials. In its journey it becomes superheated and dissolves significant amounts of materials, especially sulfides. When this mineral laden water returns to the ocean floor and mixes with the cold bottom waters, the minerals precipitate out and build up chimneys. Such an environment could have provided archeobacteria with an energy source.