From the Wikipedia article on "Geothermal energy":
"Geothermal power is considered to be renewable because any projected heat extraction is small compared to the Earth's heat content. The Earth has an internal heat content of 10^31 joules (3ยท10^15 TWh), approximately 100 billion times the 2010 worldwide annual energy consumption.[...] About 20% of this is residual heat from planetary accretion; the remainder is attributed to past and current radioactive decay of naturally occurring isotopes." -- https://en.wikipedia.org/wiki/Geothermal_energy#Renewability...
"Geothermal power is considered to be renewable because any projected heat extraction is small compared to the Earth's heat content. The Earth has an internal heat content of 10^31 joules (3ยท10^15 TWh), approximately 100 billion times the 2010 worldwide annual energy consumption.[...] About 20% of this is residual heat from planetary accretion; the remainder is attributed to past and current radioactive decay of naturally occurring isotopes." -- https://en.wikipedia.org/wiki/Geothermal_energy#Renewability...