Measuring Changes in the Atmospheric Neutrino Rate Over Gigayear
  Timescales
  Measuring the cosmic ray flux over timescales comparable to the age of the
solar system, $\sim 4.5\,$Gyr, could provide a new window on the history of the
Earth, the solar system, and even our galaxy. We present a technique to
indirectly measure the rate of cosmic rays as a function of time using the
imprints of atmospheric neutrinos in paleo-detectors, natural minerals which
record damage tracks from nuclear recoils. Minerals commonly found on Earth are
$\lesssim 1\,$Gyr old, providing the ability to look back across cosmic ray
history on timescales of the same order as the age of the solar system. Given a
collection of differently aged samples dated with reasonable accuracy, this
technique is particularly well-suited to measuring historical changes in the
cosmic ray flux at Earth and is broadly applicable in astrophysics and
geophysics.
