I remember back in AP Biology in high school, my teacher briefly mentioned during the unit on autotrophs, that there are certain types of organisms who create their own energy but do it in the absence of the sun.
To me this was a complete conundrum. In every science related class, presentation or seminar that I had attended up until this point had preached that the sun was the absolute beginning of the energy supply of Earth’s ecosystems.
However, as I delved further into this topic, I learned that extremophiles are notorious for employing the process of chemosynthesis. And this made sense, considering that places like the ocean floor near hydrothermal vents are almost always devoid of sunlight. I just never had known any autotrophs existed at these depths and brutal of environments.
In short, the sulfur-oxidizing-bacteria which do this process take in water, carbon dioxide dissolved in the ocean water and hydrogen sulfide from geothermal vents and fix all of them in such a way that it creates sugars like glucose as an energy source and sulfuric acid as a waste product.
They often aren’t the only ones who benefit from this energy production however. A lot of the time, they hold mutualistic or commensal relationships with other organisms such as plants on the ocean floor, who utilize some of the sugar that they produce. In the mutualistic cases, they often return the favor by giving these bacteria a place to live and colonize. Other organisms may also garner sugar from the bacterium when they die or by ingesting them.