Emerging evidence supports the hypothesis that Earth’s electromagnetic grid output—including its direct current (DC) potential, the Carnegie Curve and Schumann Resonance frequencies—plays a central role in maintaining and regulating circadian rhythms. While it is well-established that exposure to sunlight entrains melatonin production, this article proposes that grounding to the Earth may be equally vital in setting the cortisol rhythm. Historical research involving sensory-isolated bunker experiments revealed that removing the Earth’s natural electromagnetic fields can lead to desynchronization of the human circadian rhythm, independent of the influence of light exposure. Modern clinical studies show that sleeping while grounded significantly alters the cortisol profile, with measurable improvements in circadian regularity, sleep quality, stress response, and autonomic nervous system function. By reviewing historical and contemporary medical studies, this article proposes that the human body’s exposure to the Earth’s surface potential and resonant frequencies supports cortisol rhythm integrity and may, in some contexts, be more foundational than sunlight in regulating the day/night cycle. The Earth appears to act as a hormonal “clock setter,” particularly for the cortisol awakening response and overnight cortisol suppression, creating a tandem effect alongside melatonin to maintain a stable 24-hour biological rhythm.