The lipid bilayer of the biological membrane is a multicomponent molecular mixture capable of exhibiting compositional and structural heterogeneity. Using Fourier transform infrared spectroscopy and Monte Carlo computer simulation techniques, we report here for the first time the existence of a long-lived nonequilibrium heterogeneous lateral membrane structure composed of gel and fluid domains in a binary dipalmitoylphosphatidylcholine-dibehenoylphosphatidylcholine (DC16 PC-DC22 PC) lipid membrane. The nonequilibrium dynamic ordering process of coexisting phases following a thermal quench from the fluid state into the gel-fluid phase coexistence region is characterized by a relaxation time on the order of hours. This slow process leads to a long-lived compartmentalized percolative lateral membrane structure with a dynamic network of interfacial regions having properties different from the coexisting gel and fluid bulk phases.