Detailed calculations are carried out of the sources of energetic metastable O(1D) atoms in the atmosphere at altitudes between 80 km and 200 km, and the corresponding energy distribution functions are derived, taking account of energy transfer and quenching in collisions of the metastable atoms with the ambient atmospheric gas constituents. The energy relaxation of metastable oxygen atoms produced by O2 and O3 photolysis and O2+ dissociative recombination is determined by solving the time-dependent Boltzmann equation. The O(1D) thermalization and quenching times are obtained as functions of the altitude. The steady state distributions of metastable O(1D) are computed and used for the determination of the parameters characterizing the nonthermal O(1D) atoms. The nonthermal atoms comprise 4--6% of the distribution, and their effective temperatures are larger by 25--46% than the local temperatures of the ambient gas. The role of hot metastable oxygen atoms in the production of vibrationally excited OH molecules is analyzed.