List of top Geology and Geophysics Questions on Geothermics

Which one among the following factors contributes the least amount of heat to the Earth's annual heat budget?
The heat flux at the Earth's surface is 60 mWm\(^2\). If the thermal conductivity at the surface is 2.5 Wm\(^{-1}\)°C\(^{-1}\), the geothermal gradient is \(\underline{\hspace{1cm}}\) °C/km. (round off to integer)