On Earth Day this year, what I’m thinking about is not the beauty of our planet, or the fragility of it, but how quickly it’s changing. Here are a few stories that highlight those changes, as well as a few stories that discuss what we humans might do about them, should we decide to take dramatic action. What’s at stake is not the Earth—the planet has been through much, much worse in the last 4 billion years. It’s civilization that’s on the line.