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We study the Rayleigh-Taylor instability for two miscible, incompressible, inviscid fluids. Scale-invariant estimates for the size of the mixing zone and coarsening of internal structures in the fully nonlinear regime are established following techniques introduced for the Saffman-Taylor instability in [Otto and Menon, Commun.Math.Phys., 2005]. These bounds provide optimal scaling laws and reveal the strong role of dissipation in slowing down mixing.