The dynamics in adsorbed homopolymer layers were probed using self-exchange studies with the model system poly(ethylene oxide), PEG, adsorbed on silica from aqueous solution. The latter constitutes a good solvent for PEO. The influence of layer age and molecular weight was investigated. The self-exchange traces themselves were bimodal, fitting a simple noncooperative exchange model at short times and then switching over to stretched exponential behavior. In mature PEO layers (where no further influence of aging was found), higher molecular weight layers were less mobile than lower molecular weight layers, with a linear influence of molecular weight on the stretched exponential time constant and on the time constant describing the initial stages of exchange. The stretching exponent was 0.34 +/- 0.04, independent of molecular weight. Also, the approach of newly formed layers to the mature state followed a single exponential, with faster maturation of layers of longer chains.