Chemolithotrophs near hydrothermal vents support a variety of life forms. Why is this analogous to photosynthetic microbes supporting life forms closer to the surface of the planet?
Because all life forms need some energy source, electron source, and carbon source. Chemolithotrophs, if consumed by other microbes, could serve as all three. This is very similar to the role that photosynthetic microbes play in the top levels of the oceans/lakes.
Because chemolithotrophs will also utilize energy from sunlight to form their sugars/get their chemical energy...much like photosynthetic microbes.
Because chemolithotrophs also pull in carbon dioxide as their carbon source, just like photosynthetic microbes.
Because photosynthetic microbes utilize heat energy from the sun as an energy source. Chemolithotrophs utilize heat energy from hydrothermal vents, but it's still heat energy. This makes both microbes similar.