  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^0's 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.
