Earth gets treated as a single heat-driven machine, and the film follows the forces that keep reshaping it from the inside out. Cameras descend into the lava lake of Mount Nyiragongo in the Democratic Republic of Congo, drop to the 11-kilometer floor of the Mariana Trench, and watch technicians repair telecommunication cables thousands of meters underwater. Closer to home, engineers retrofit California's Memorial Stadium, built directly across the Hayward Fault, and hydrologists map roughly 100,000 square miles of rivers running beneath Florida's surface. A sequence that visually drains the oceans exposes canyons and volcanic ridges normally hidden by water, tying the seafloor's geography back to the superheated core generating the planet's magnetic field. The film's answer to its title question comes from measuring mountains not from sea level but from base to peak, a reframing that puts a volcano ahead of Everest. Expository narration links each location back to the same underlying argument about the planet's internal engine.