sM_dust vs. Age_main diagrams colour-coded in sSFR for Hi-z LBGs. Low-sSFR objects are the oldest objects and low-sM_dust objects are the youngest ones. The decline of sM_dust is interpreted as an efficient dust removal (destruction or outflow) with a time-scale of ∼500 Myrs. This diagram makes it possible to obtain an estimate of the dust removal grain in these Hi-z galaxies. Symbols coded as in Fig. 1. From left to right, the vertical dotted lines show 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, and 99% of the integrated SFR, assuming a delayed SFH.