Richard Alley, a geologist at Penn State who once worked for an oil company, opens this episode by tracing how Earth's climate has swung between ice-covered and ice-free states across deep time, using fieldwork in Greenland and Antarctica to show how ice cores record those shifts. He turns from that history to the present math: fossil fuels supply roughly 80 percent of global energy, nuclear under 5 percent, hydropower about 6 percent, and solar, wind, and geothermal combined just 1 percent, though that last figure is climbing fast. The film looks for unexpected converts to clean energy, including the US Pentagon working to cut its fuel dependence and wind farmers in West Texas turning ranchland into turbine fields. Alley's case is that humans have always been energy-dependent, from the first controlled fires onward, and that a population heading toward 10 billion makes the choice of what powers civilization a matter of survival, not preference. It's the opening installment of a mini-series built around that argument.