One estimate of the original temperature of Earth is 7000 F. Using this value and the following properties for Earth’s crust, Lord Kelvin obtained an estimate of 9.8 10 7 years for the Earth’s age....

One estimate of the original temperature of Earth is 7000F. Using this value and the following properties for Earth’s crust, Lord Kelvin obtained an estimate of 9.810⁷
years for the Earth’s age.

Comment on Lord Kelvin’s result by considering the exact expression for unsteady-state conduction in one dimension