Sixty-five million years ago, an asteroid crashed into the Earth, ending the Cretaceous era. All that remains from that distant time are fossils, including fragments of petrified trees, found notably in the northern Sahara—at that time a lush forest. Having collected some of these fragments, Alicja Kwade has used them in an attempt to reconstitute trees. She then pulverised them, turning them back into sand—the same sand (silicon dioxide) that penetrated and transformed them, as if time were repeating itself, deliberately going backwards and forwards, and then backwards again. We are made to doubt our own perception, because the comparison is troubling: are they trees, or is it sand, or stone?