Using an exact-diagonalization technique on small clusters, we calculate the spin and density excitation spectra as well as the temperature dependence of the specific heat for the triangular-lattice t-J model with the multiple-spin exchange interactions, whereby we consider the low-energy excitations of the two-dimensional liquid 3He adsorbed on graphite. We find that, for a relevant set of the parameter values, the spectral weight for the spin excitations is concentrated on a very low-energy region, while that of the density excitations extends over a wide energy range, indicating the clear separation of their energy scales. The double-peak structure in the temperature dependence of the specific heat is also obtained. © 2009 IOP Publishing Ltd.