So far, we have examined the history of our planet through the lens of a geologist, in which we observe the products captured in the rock record and try to interpret how they originate in the context of the complex interactions of geological processes over long geological timescales. This includes relocation of land masses through plate tectonics over hundreds of million-year Wilson cycles, as discussed in Chapters 5 and 10, to shorter-term sea-level and climate changes that occur over tens of thousands of years associated with orbital cycles reviewed in Chapter 18. We have also reviewed some of the major catastrophes in Earth history, with a focus on the mass extinctions that marked the end of the Paleozoic and Mesozoic eras (Chapters 11 and 13). In this chapter, we consider the idea that human activities over fewer than 300 years are now so profound that they might leave a permanent record in the geology of our planet.