AbstractThepythia 6 Monte Carlo (MC) event generator, commonly used in collider physics, is interfaced for the first time with a fast transport simulation of a hydrogen atmosphere, with the same density as air, in order to study the properties of extended atmospheric showers (EAS) produced by cosmic-ray protons with energies–1020 eV. At variance with the hadronic MC generators (epos-lhc,qgsjet, andsibyll) commonly used in cosmic-ray physics,pythiaincludes the generation of harder hadronic jets and heavy (charm and bottom) quarks, thereby producing higher transverse momentum final particles, that could explain several anomalies observed in the data. The electromagnetic, hadronic, and muonic properties of EAS generated with various settings ofpythia 6, tuned to proton–proton data measured at the LHC, are compared to those fromepos-lhc,qgsjet 01,qgsjet-ii-04, andsibyll 2.1. Despite their different underlying parton dynamics, the characteristics of the EAS generated withpythia 6 are in between those predicted by the rest of the MC generators. The only exceptions are the muonic components at large transverse distances from the shower axis, wherepythiapredicts more activity than the rest of the models. Heavy-quark production, as implemented in this study for a hydrogen atmosphere, does not seem to play a key role in the EAS muon properties, pointing to nuclear effects as being responsible for the muon anomalies observed in the air-shower data.