In his book “The periodic system” Primo Levi tells how a carbon atom can pass from a rock to a leaf, to a human being, and then become a gas in the atmosphere, waiting to return perhaps, “through the narrow door of photosynthesis”, in the cycle of life. Following the path indicated by the story, in the workshop visitors will get involved with the simulation of the carbon cycle, experimenting with some of the reactions involved in the continuous migration of atoms from one compound to another, examining their complexity and becoming aware of how the actions human beings we are changing the millennial balance of the Earth. The public will be led to reflect, trying to follow the path of the literary protagonist, the carbon atom, on how it recombines from the reagents into different products, with the breaking and formation of new bonds and how these reactions cyclically involve both the inorganic world than the world of the living.