Mineral spirits are simple hydrocarbons with a chain length of C7 to C12 .
Chemistry 101: Methane, a gas, is one carbon atom surrounded by 4 hydrogen atoms. When you connect 4 carbon atoms in a chain, they become butane, a liquid. At chain lengths above about 12, you get a solid, or basically paraffin. So mineral spirits are a liquid hydrocarbon mix somewhere in the middle.
Mineral spirits evaporate (slowly), where they are exposed to UV light, cosmic rays and the 21% oxygen content of our atmosphere. Like all organic molecules, they do break down (oxidize) into water and carbon dioxide.
This is why mineral spirits are about the most enviro option for degreasing and cleaning. The solvent can be used multiple times, and the bad stuff filtered out and discarded. Ultimately, the solvent evaporates and is broken down in the air.
Contrast this to water-based cleaning products, including anything: 'green'. Being water-based, they are ineffective at actually degreasing. Chemistry 201: polar molecules (water) only minimally mix with non-polar (grease and oil) molecules. So with the water-based products, you have to use far greater volumes, and far more mechanical scrubbing to get the same effect as with a hydrocarbon-based degreaser. And where does the mix of oil/grease and water go? Down the drain of course, where it causes far more enviro harm than with mineral spirits.