  In this paper we use invariant theory to develop the notion of cohomological
detection for Type I classical Lie superalgebras. In particular we show that
the cohomology with coefficients in an arbitrary module can be detected on
smaller subalgebras. These results are used later to affirmatively answer
questions, which were originally posed in \cite{BKN1} and \cite{BaKN}, about
realizing support varieties for Lie superalgebras via rank varieties
constructed for the smaller detecting subalgebras.
