The impact of large meteorites on the moon or earth is discussed on the basis of a one-dimensional idealization of the flow problem, in which a plane shock wave is considered in both meteorite and impact surface. Conditions are discussed under which such a model can yield physically valid estimates of pressure and temperature generated on explosive impact of meteorites Computations are carried out for an equation of state and internal energy from the statistical Thomas-Fermi atom model; departures from complete degeneracy are taken into account by means of results of a first-order perturbation with respect to temperature. It is assumed that the meteorite and impact surface are composed of the same pure element, taken as silicon, iron, and an average element (in a sense defined) for meteorites. The range of impact velocity considered goes up to the limit possible for meteorite origin in the solar system, which is well in excess of Whipple's estimates of mean atmospheric velocity for meteorite falls Over this range, values of compression ratio, pressure, and temperature behind the shocks and of shock velocities are exhibited as functions of impact velocity; at the lowest and the highest velocities, results are only qualitative. Shock temperatures computed for iron agree reasonably with extrapolation of experimental data of Walsh and Christian for copper at lower pressures. The results yield pressures and temperatures of explosive magnitude behind the shock waves, in confirmation of the views of Gifford and Baldwin. Computed fusion temperatures behind the shocks show no inconsistency with Urey's mechanism of formation of lunar maria.