Both are prefixes and suffixes of origin Greek. GEO means Earth, and thermos, meaning heat. Examples: Geography (science that studies and describes them phenomena physical and human in the surface of the land), peak (distance maximum of a body in movement that revolves around it land), thermometer (instrument that serves for measure the temperature or heat that exists in a body), isothermal (that has or maintains the same temperature or heat).
GEO - gea - and also ge - are prefixes derived from the Greek term ge ges which means land. They form words such as geography, exclusivists, geodesy, geophysics, geology, geometry, geothermal... There are also suffixes - geo,-gea-geico has the same meaning as Apogee and perigee. The Thermo - and term - prefixes derived from therme thermes ( heat ) and form words as Thermopylae, thermometer, thermostat, thermodynamics, heat therapy... Also there is the infix - Thermo - and the suffix - Thermo, - therm, - heat,-termano,-termancia as in isothermal, hypothermia, insulation, geothermal energy, diathermic