Presenter notes: Open with a challenge rather than a definition. Ask the class to name one thing they used this morning that did not come from nature. Give them a full minute and take every answer seriously. Plastic comes from petroleum. A mobile phone is metal and glass and petroleum. Even the electricity came from falling water or burning coal. Nobody will find one, and that failure is the opening you want. Then say the sentence: there is nothing in this room that did not start in the ground, in a river, or in a living thing.