  Paleo-detectors are a proposed experimental technique to search for dark
matter (DM). In lieu of the conventional approach of operating a tonne-scale
real-time detector to search for DM-induced nuclear recoils, paleo-detectors
take advantage of small samples of naturally occurring rocks on Earth that have
been deep underground ($\gtrsim 5$ km), accumulating nuclear damage tracks from
recoiling nuclei for $\mathcal{O}(1)$ Gyr. Modern microscopy techniques promise
the capability to read out nuclear damage tracks with nanometer resolution in
macroscopic samples. Thanks to their $\mathcal{O}(1)$ Gyr integration times,
paleo-detectors could constitute nuclear recoil detectors with keV recoil
energy thresholds and 100 kilotonne-yr exposures. This combination would allow
paleo-detectors to probe DM-nucleon cross sections orders of magnitude below
existing upper limits from conventional direct detection experiments. In this
article, we use improved background modeling and a new spectral analysis
technique to update the sensitivity forecast for paleo-detectors. We
demonstrate the robustness of the sensitivity forecast to the (lack of)
ancillary measurements of the age of the samples and the parameters controlling
the backgrounds, systematic mismodeling of the spectral shape of the
backgrounds, and the radiopurity of the mineral samples. Specifically, we
demonstrate that even if the uranium concentration in paleo-detector samples is
$10^{-8}$ (per weight), many orders of magnitude larger than what we expect in
the most radiopure samples obtained from ultra basic rock or marine evaporite
deposits, paleo-detectors could still probe DM-nucleon cross sections below
current limits. For DM masses $\lesssim 10$ GeV/$c^2$, the sensitivity of
paleo-detectors could still reach down all the way to the conventional neutrino
floor in a Xe-based direct detection experiment.
