If Aliens Exist, Here's How We'll Find Them - Issue 111: Spotlight

In this special issue we are reprinting our top stories of the past year. This article first appeared online in our "Wonder" issue in February, 2021. Suppose aliens existed, and imagine that some of them had been watching our planet for its entire four and a half billion years. What would they have seen? Over most of that vast timespan, Earth's appearance altered slowly and gradually. Continents drifted; ice cover waxed and waned; successive species emerged, evolved, with many of them becoming extinct. But in just a tiny sliver of Earth's history--the last hundred centuries--the patterns of vegetation altered much faster than before. This signaled the start of agriculture--and later urbanization.