In environments that lack oxygen, some organisms have developed a way to break down intorganic molecules in order to produce energy. what is this process called?

The above mentioned process is called as Anaerobic respiration

Explanation:

All organisms need oxygen to produce energy but in some prokaryotes and eukaryotes they lack the presence of oxygen in their environment. Hence they have adapted a strategy called anaerobic respiration to break down the inorganic molecules to produce energy.

They use carbon dioxide and release methane as the by product. The process of glycolosis helps.  All types of fermentation happens anaerobically here. It helps down to break down the fuels and produce energy. This energy is utilized for their life function.  

thinking it would be physical characteristics