Geothermal energy is heat from within the Earth that has been present since the original formation of the planet. It is contained in the rocks and fluids beneath the earth's crust, distributed through layers of magma several thousand miles thick. This enormous store of heat helps keep Earth’s crust from becoming permanently frozen by dispersing the heat to the surface. Atmospheric temperatures can overtake the natural warmth of soil in some regions and seasons, but just a few feet below the surface, the Earth maintains a near-constant temperature, in contrast to the summer and winter extremes of the ambient air above ground.
Air is pumped from within the greenhouse, through a length of underground pipes. As it travels, it absorbs warmth from the surrounding soil and arrives back in the greenhouse at a steady temperature of 55 to 60 degrees F, even when the outside temperature dips well below freezing.
