Kelvin's estimates of the age of the Earth, and his attendant attacks on Darwin and uniformitarianism, were seen as dispositive for nearly five decades (Dalrymple, 29; Hallam, 108).
The following explanations (1) of Kelvin's method, (2) its significance through history, and (3) modern invocations of Kelvin by creationists will help shed light on the larger conflict over the age of the Earth.
The idea that Earth had begun as an incredibly hot sphere of liquid dates back to Descartes and Leibnitz.
This assumed initial condition was the linchpin for Kelvin's entire method (Hallam, 110).
Bits of material at the surface would sink before solidifying, creating convection currents that kept the Earth at a uniform temperature until solidification began at the core (Hallam, 110; Knopf, 445).
Kelvin needed to know: (1) the temperature at Earth's core, (2) the temperature gradient with regard to depth below the surface, and (3) the thermal conductivity of rocks.
Kelvin derived his estimate from quantitative and repeatable measurements, physical principles of natural laws, and elegant math (Dalrymple, 33).Some of the great scientists, carefully ciphering the evidences furnished by geology, have arrived at the conviction that our world is prodigiously old, and they may be right but Lord Kelvin is not of their opinion.He takes the cautious, conservative view, in order to be on the safe side, and feels sure it is not so old as they think.Nor did it address the great majority of geologic time since the Weald sits at the top of the geologic column.The net result of the argument was that Earth must have existed for billions of years (Lewis, 25) or, in other words, be of almost limitless age (Hallam, 108).