Meteoritic organic matter records primitive oxygen reservoirs of the solar system.

Unraveling the complex formation and alteration history for extraterrestrial organic matter is key to understanding the chemical evolution of the solar system (SS) and potentially even life's emergence on Earth. In this study, we performed high-precision triple oxygen isotope measurements on insoluble organic matter (IOM) sourced from a diverse suite of carbonaceous chondrites (CCs). Remarkably, the IOM from primitive Type 1 and 2 CCs-including CI, CM, CR, Bells, and Tarda-have oxygen isotope compositions that cluster on or near the CCAM line, which is itself related to the mixing of primitive oxygen isotope reservoirs residing within the early SS. This finding suggests that primitive meteoritic OM acquired oxygen of primitive origin and that those isotopic signatures have been minimally altered by parent body processes, offering critical constraints to assess the synthetic origin of meteoritic OM and evolution of SS oxygen reservoirs.