Geothermal energy can be used to cool homes because:
a. warm air comes from the atmosphere.
b. the core is hot.
c. cool air comes from deep within the crust.

B.

Im not sure of the depth ( 8ft 16ft?) can't remember, the ground temperature is always about 70 degrees F. that temperature is from the heat of the core dissipating outwards. So geothermal conditioning is simply forcing the air in  that are in the ground, into your home

If its history of, then b) because a) implies only present day (now)