Аннотация:Quasars remain one of the most powerful probes of the early Universe, providing measurements and constraints for re‐ionization, early structure formation, and early chemical enrichment epochs [1], [2], [3]. The obscured phase of QSOs evolution, as well as their accretion history, can be best followed by observing QSOs bright in MeV gamma‐rays [4]. By analysing resonant absorption troughs in spectral energy distribution of flaring QSOs one can measure the (baryonic) absorbing column, e.g. baryonic content, and metallicity of the QSO host galaxy [5], while the flare strength will give information on the accretion rate of the QSO powering supermassive black hole. By measuring the baryonic absorbing column for QSOs at different redshifts one can follow the early obscured evolution of AGN, as well as the evolution of the IGM transmission at the end of the cosmic re‐ionization epoch, while absorption by metals constrain the early chemical evolution of the IGM. These possibilities can be explored in the near future by observations with instruments like, already launched, Fermi‐GLAST. Even earlier phases of the Universe evolution, at redshifts z>6, can be studied by applying the gamma‐ray resonance absorption method to the GRBs prompt emission anaysis. This type of a study can be done in a foreseeable future with a MeV‐range covering space instrument like GRIPS