A rise in temperature with increase in depth is observed in mines and deep wells.
These evidence along with molten lava erupted from the earth’s interior supports that the temperature increases towards the centre of the earth.
While in the upper 100kms, the increase in temperature is at the rate of 120C per km and in the next 300kms, it is 200C per km. But going further deep, this rate reduces to mere 100C per km.
It is assumed that the rate of increase in the temperature beneath the surface is decreasing towards the centre.
Temperature is always increasing from the earth’s surface towards the centre.
The temperature at the centre is estimated to lie somewhere between 30000C and 50000C, maybe that much higher due to the chemical reactions under high-pressure conditions.