After watching an oil spill coat San Francisco Bay near his home in 1971, he stopped riding in cars entirely and walked instead, a choice that lasted 22 years, and not long after he stopped speaking too, holding that silence for 17 of them. He earned a PhD in land management along the way, walked across the country, and later served as a UN Environment Program goodwill ambassador. He wrote about it all in his memoir, Planetwalker, and says the years of listening taught him more about the land and the people on it than the years of talking ever had.