ɪt hˈæzbiːn pɹəpˈoʊzd ðæt ˌɛmˌɑːɹɹˈoʊz sˈʌtʃ ɐz mˈaɪɾəsˌoʊmz ɪvˈɑːlvd ɪn ænˈɑːksɪk mɚɹˈiːn ɛnvˈaɪɹənmənts wˌɪtʃ pɹɪdˈɑːmᵻnˌeɪɾᵻd dˈʊɹɹɪŋ ðə pɹˌoʊtɹəzˈoʊɪk, ðˈʌs ɛksplˈeɪnɪŋ ðɛɹ ˌænɛɹˈoʊbɪk mˌɛɾəbˈɑːlɪk fˌʌŋkʃənˈælᵻɾi.
It has been proposed that MROs such as mitosomes evolved in anoxic marine environments which predominated during the Proterozoic, thus explaining their anaerobic metabolic functionality.