Conventional dark matter detectors are like a soccer goalkeeper waiting for a powerful shot while the ball barely rolls. The invisible particles filling our galaxy often move too slowly to be noticed by sensitive sensors. But nature builds its own accelerators: when a massive star collapses and explodes as a supernova, it hurls dark matter particles with tremendous force, like splinters from an axe.
Such an accelerated "projectile" slams into atoms in ancient minerals and knocks them out of place, leaving a microscopic trace, like a scratch on glass. In olivine crystals that have lain in Earth's crust for billions of years, these scratches accumulate. Researchers calculated how many traces particles of different masses could leave — from a few MeV to hundreds of MeV (for comparison: the electron mass is about 0.5 MeV). They also accounted for background "noise": neutrinos, neutrons from uranium, and nuclear recoils from thorium.
The analysis showed that paleodetectors can detect dark matter in a parameter region that neither current nor planned experiments can reach. Particularly interesting are supernova explosions in our galaxy: their particle flux over geological timescales leaves a distinct signature in minerals. The accumulated exposure over a billion years provides a sensitivity gain of hundreds to thousands of times compared to laboratory instruments that operate for only a few years.
Thus, an ancient rock becomes a time machine. The very slow, almost elusive dark matter that modern traps cannot see turns out to be locked in the crystal lattice: we just need to read these traces.
Olivine is not only found on Earth: it is present in lunar soil and meteorites. Extraterrestrial samples might hold an even cleaner record of dark matter, untainted by geological processes.
In Peter Watts's novel Blindsight, alien life uses crystalline structures to store information over geological timescales — much like our paleodetectors.