A natural question in the
study of geometric operators is that of how much information is needed to estimate
the eigenvalues of an operator. For the square of the Dirac operator, such a question
has at least peripheral physical import. When coupled to gauge fields, the lowest
eigenvalue is related to chiral symmetry breaking. In the pure metric case, lower
eigenvalue estimates may help to give a sharper estimate of the ADM mass of
an asymptotically flat spacetime with black holes. We use three tools to
estimate the eigenvalues of the square of the (purely metric) Dirac operator: the
conformal covariance of the operator, a patching method and a heat kernel
bound.