  We prove a $C^1$ version of a conjecture by Pugh and Shub: among partially
hyperbolic volume-preserving $C^r$ diffeomorphisms, $r>1$, the stably ergodic
ones are $C^1$-dense.
  To establish these results, we develop new perturbation tools for the $C^1$
topology: linearization of horseshoes while preserving entropy, and creation of
"superblenders" from hyperbolic sets with large entropy.
