  A new class of high temperature superconductors based on iron and arsenic was
recently discovered, with superconducting transition temperature as high as 55
K. Here we show, using microscopic theory, that the normal state of the iron
pnictides at high temperatures is highly anomalous, displaying a Curie Weiss
susceptibility and a linear temperature dependence of the resistivity. Below a
coherence scale T*, the resistivity sharply drops and susceptibility crosses
over to Pauli-like temperature dependence. Remarkably, the
coherence-incoherence crossover temperature is a very strong function of the
strength of the Hund's rule coupling J_Hund. On the basis of the normal state
properties, we estimate J_Hund to be 0.35-0.4 eV. In the atomic limit, this
value of J_Hund leads to the critical ratio of the exchange constants
J_1/J_2~2. While normal state incoherence is in common to all strongly
correlated superconductors, the mechanism for emergence of the incoherent state
in iron-oxypnictides, is unique due to its multiorbital electronic structure.
