The Earth's electric field is mainly a continuous direct current (DC) producing field.
Throughout history, life on the planet has attuned our biology to this subtle field. By comparison, home wiring systems in the U.S., use 60-cycle per second alternating current (AC). Unless at very low frequency (less than 10 cycles per second) and/or low power, alternating current is foreign to our biology.
This, and other forms of man-made environmental electromagnetic fields (EMFs) are being researched as factors in a variety of stress-related responses.
Many people are sensitive to EMFs. Studies show an association, but not cause and effect, between living new power lines (or exposure to EMFs on the job) and a higher range of health problems.