THE indelible marks made by cosmic rays that bombard the Earth can reveal whether our ancestors spent time and effort looking for the best raw materials for stone tools or simply used what came easily to hand.
Cosmic rays are high-energy particles thought to come from supernova explosions. These produce a shower of secondary particles when they collide with atomic nuclei in the upper atmosphere. Both primary and secondary particles can slam into the nuclei of atoms in the Earth’s crust to form stable radioactive isotopes. For instance, cosmic rays interact with the oxygen in flint and form beryllium-10.
These…
