A recent trip to Mexico’s Teotihuacan incited a most thought provoking question: “What will we leave behind?” from one of my blog followers. If humans were to disappear off the face of the planet tomorrow, in just a few centuries, the Earth would look as if we were never here. Our plastic would be buried beneath mountains of sediment, our cities would collapse, crumble, or be washed away. And if their facades remained, almost nothing would remain that would identify us or places.