We argue that ultrahigh energy cosmic ray collisions in the Earth atmosphere can probe the strange quark density of the nucleon. These collisions have center-of-mass energies agt 10^{4.6} A GeV, where A geq 14 is the nuclear baryon number. We hypothesize the formation of a deconfined thermal fireball which undergoes a sudden hadronization. At production the fireball has a very high matter density and consists of gluons and two flavors of light quarks (u,d). Because the fireball is formed in the baryon-rich projectile fragmentation region, the high baryochemical potential damps the production of u bar u and d bar d pairs, resulting in gluon fragmentation mainly into s bar s. The strange quarks then become much more abundant and upon hadronization the relative density of strange hadrons is significantly enhanced over that resulting from a hadron gas. Assuming the momentum distribution functions can be approximated by Fermi-Dirac and Bose-Einstein statistics, we estimate a kaon-to-pion ratio of about 3 and expect a similar (total) baryon-to-pion ratio. We show that, if this were the case, the excess of strange hadrons would suppress the fraction of energy which is transferred to decaying pi^0s by about 20%, yielding a sim 40% enhancement of the muon content in atmospheric cascades, in agreement with recent data reported by the Pierre Auger Collaboration.
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