Isotopes, Vikings, Mars

We are perishable matter yearning for meaning, and time is both the matter and the meaning of our lives. “Time is a river that sweeps me along but I am the river,” Borges wrote in 1940. “Time is the substance I am made of.”

Around the same time, the chemist Willard Libby had a revolutionary insight that brought physics to the poetry of time, measurement to the mystery of this substance we are made of.

Discus chronologicus — a German depiction of time from the early 1720s, included in Cartograph...