It makes sense to incorporate Earth science–related terms into the Drake equation, Wong said. “It seems like, at least for the evolution of life on Earth, it was crucial for there to be oceans and continents as well as plate tectonics.” But the fractions of planets hosting long-lived plate tectonics and both oceans and continents that Stern and Gerya proposed are highly uncertain, he said. “I don’t know how, honestly, to try even to get at these numbers.”