  The opacity of the Earth to incident ultra high energy neutrinos is directly
connected with the behaviour of the neutrino - nucleon ($\sigma^{\nu N}$) cross
sections in a kinematic range utterly unexplored. In this work we investigate
how the uncertainties in $\sigma^{\nu N}$ due the different QCD dynamic models
modify the neutrino absorption while they travel across the Earth. In
particular, we compare the predictions of two extreme scenarios for the high
energy behaviour of the cross section, which are consistent with the current
experimental data. The first scenario considered is based on the solution of
the linear DGLAP equations at small-$x$ and large-$Q^2$, while the second one
take into account the unitarity effects in the neutrino - nucleon cross section
by the imposition of the Froissart bound behaviour in the nucleon structure
functions at large energies. Our results indicate that probability of
absorption and the angular distribution of neutrino events are sensitive to the
the QCD dynamics at ultra high energies.
