Lord Kelvin’s careful and multiply-supported lines of reasoning arguing that the Earth could not possibly be so much as a hundred million years old, all failed simultaneously in a surprising way because that era didn’t know about nuclear reactions.
I’m told that the biggest reason Kelvin was wrong was that, for many years, no one thought about there being a molten interior subject to convection:
Perry’s [1895?] calculation shows that if the Earth has a conducting lid of 50 kilometers’ thickness, with a perfectly convecting fluid underneath, then the measured thermal gradients near the surface are consistent with any age up to 2 billion or 3 billion years. Recognizing that heat transfer in the mantle cannot be perfectly efficient, Perry subsequently modeled the deep interior as a solid with high “quasi-diffusivity.” His results agreed with the original simple calculation in suggesting that the Earth could be several billions of years old. Full calculations of convection in the mantle (which were impossible until the advent of computers) confirm that Perry’s reasoning was sound.
In other words, Perry was able to reconcile a physical calculation of Earth’s thermal evolution with the great age that geologists required. Perry needed nothing more than to introduce the idea that heat moved in the deep interior of the Earth more readily than it moved in the outermost layers. Yet to this day, most geologists believe that Kelvin’s (understandable) mistake was not to have known about Earth’s internal radioactivity.
Of course, 2-3 billion is also too young, and with radioactive decay we can raise the age to ~4 billion years.
But wait, shouldn’t convection also increase the cooling rate, so that the Earth in Perry’s model should be cooler even if it were the same age as Kelvin’s Earth? I am confused.
P.S. I find this piece abstract and hard to decipher, especially the discussion of law/Law; your early works were easier. More examples and detail are needed to connect the words to reality.
I’m told that the biggest reason Kelvin was wrong was that, for many years, no one thought about there being a molten interior subject to convection:
Of course, 2-3 billion is also too young, and with radioactive decay we can raise the age to ~4 billion years.
But wait, shouldn’t convection also increase the cooling rate, so that the Earth in Perry’s model should be cooler even if it were the same age as Kelvin’s Earth? I am confused.
P.S. I find this piece abstract and hard to decipher, especially the discussion of law/Law; your early works were easier. More examples and detail are needed to connect the words to reality.