Subtraction: “The Earth is hungry to subtract” was the opening line of a poem I wrote in the mid-1990s after a series of earthquakes in the Americas, Anatolia, and Eurasia. The poem’s speculation involved the opening of fissures that would come to swallow up the whole of humanity as an aging Earth grown tired of the burden of its surface dwellers. But the subtraction I failed to take into consideration is molecular, viral, the sickness not below but on the surface, between human beings. For fifty years now, new viral strains, most carried by birds, bats, rodents, and simians, have begun contaminating humanity’s vulnerable inner fluids. Imagine, please, a coronavirus-like epidemic of Ebola, whose latest strain is menacing several African nations. The result might be more like what was imagined in the postapocalyptic film “28 Days Later.” At a more existential level, consider as well that Earth is aging and by all accounts has already lived about half its projected lifespan, 5 billion years, a lifetime that will ultimately come to a quietly cold end after the sun becomes a white dwarf. Unless the inhabitants of Earth find and colonize a new home, they will vanish. In a time when many debate whether climate change is real — few choosing to study the fate of dinosaurs or to meditate on ancient ice ages — the reality that the planet itself is entirely mortal dawns only on astronomers. And yet the real tick-tock is not a social media platform, but the sound of actual time passing, in the end bringing my poem’s prophecy of subtraction to fruition.