The rate at which Earth's temperature increases with increasing depth into its interior is known as the geothermal gradient. The geothermal gradient varies depending on several factors, including the location, geological conditions, and depth. On average, the geothermal gradient is estimated to be approximately 25 to 30 degrees Celsius per kilometer (°C/km).
This means that for every kilometer of depth below the Earth's surface, the temperature increases by about 25 to 30 degrees Celsius. However, it's important to note that this is an average value, and the actual geothermal gradient can vary in different regions and geological settings.
As you go deeper into the Earth, the temperature continues to increase due to the heat generated by radioactive decay of elements, residual heat from the planet's formation, and conduction from the Earth's core. In the Earth's core, temperatures are estimated to reach several thousand degrees Celsius.