Evolution of the temperature (left panel), the gas surface density and dust surface density (solid and dotted lines, middle panel), and optical depth (right panel) at λ = 1.3 mm (solid lines) and λ = 9.0 mm (dotted lines) as a function of orbital radius at different disc ages. During the build-up of the disc and shortly after (0.25 Myr), the disc is optically thick out to ~40 au. Up to 1 Myr the disc remains optically thick within ~10 au, and after this the disc is optically thin except for the inner ~1 au. The dashed line shows a model with strong viscous heating and low angular momentum at 1 Myr. The temperature corresponds in this case well to the 0.5 Myr case with weak viscous heating.