PeV cosmic rays: a window on the leptonic era?

It is shown that a variety of characteristic features of the high-energy hadronic cosmic-ray spectra, in particular the abrupt changes in the spectral index that occur around 3 and 300 PeV, as well as the corresponding changes in elemental composition that are evident from kinks in the 〈Xmax〉 distribution, can be explained in great detail from interactions with relic Big Bang antineutrinos, provided that the latter have a rest mass of ∼0.5 eV/c2.