Geophysical flows, such as the atmosphere and the ocean of the Earth, exhibit continuous energy spectra associated with coexisting motions over a broad range of length scales. On the one hand, long-lived coherent structures appear at the large scales, similarly to 2D turbulence. On the other hand, the three-dimensional character of the system becomes important at smaller scales. To understand how these different kinds of motions are maintained, a first step is to understand in an idealized framework how the energy is transferred across scales in turbulent fluids subjected to rotation and density stratification. These two ingredients break isotropy, and the standard 3D Kolmogorov cascade scenario is no longer valid. Numerical simulations show that the energy can be transferred downscale or upscale depending on the Froude and Rossby numbers. In this talk, I will adapt a theoretical argument from statistical mechanics, originally used by Kraichnan for 2D and 3D homogeneous isotropic turbulence, to discuss the energy cascade phenomenologies in rotating and stratified turbulence.