  Neutrinos have two properties that make them fairly unique from other known
particles: extremely low cross sections and flavor changing oscillations. With
a good knowledge of the oscillation parameters soon in hand, it will become
possible to detect low-energy atmospheric neutrinos sensitive to the forward
elastic scattering off electrons in the Earth's core providing a measurement of
the core properties and the matter effect itself. As the dynamics of the
Earth's core are complicated and in a difficult to probe environment,
additional information from upcoming neutrino experiments will provide feedback
into our knowledge of geophysics as well as useful information about exoplanet
formation and various new physics scenarios including dark matter. In addition,
we can probe the existence of the matter effect in the Earth and constrain the
non-standard neutrino interaction parameter $\epsilon_{ee}^\oplus$. We show how
DUNE's sensitivity to low-energy atmospheric neutrino oscillations can provide
a novel constraint on the density and radius of the Earth's core at the 9\%
level and the Earth's matter effect at the 5\% level. Finally, we illuminate
the physics behind low-energy atmospheric neutrino resonances in the Earth.
