Let Mg,l be the moduli space of stable algebraic curves of genus g with l marked points. With the operations that relate the different moduli spaces identifying marked points, the family (Mg,l)g,l is a modular operad of projective smooth Deligne-Mumford stacksM. In this paper, we prove that the modular operad of singular chains S∗(M;Q) is formal, so it is weakly equivalent to the modular operad...