The process by which an autotroph obtains energy from inorganic compounds instead of light is called chemosynthesis.

Here's a breakdown:

* Autotroph: An organism that can produce its own food from inorganic sources.

* Chemosynthesis: The process of using energy from inorganic compounds (like hydrogen sulfide, methane, or ammonia) to produce organic compounds.

This is in contrast to photosynthesis, where organisms use sunlight as their energy source.

Chemosynthetic organisms are often found in extreme environments like deep-sea vents, where sunlight is absent. These organisms play a crucial role in the ecosystems they inhabit, forming the base of the food chain.