This phrase is often used for showing surprise, although most people now say WTF. I remember being in the men’s room one day when someone else entered as I was finishing up my business, and I heard them exclaim, ‘What on earth is that terrible smell, was someone eating dead rats in here?” I laughed but made no response, as I hurried out of there. I will get into my topic now, but I always feel it is good to express some levity in the beginning. I do realize that sometimes it is best to avoid toilet humor, but this is a technical article which may cause me to lose some of my readers.
My story concerns the study of heat and it involves four rather famous people, Georges-Louis Leclerc, Comte de Buffon a French naturalist, mathematician, cosmologist, and encyclopedist, Jean Baptiste Joseph Fourier a French mathematician and physicist, Lord Kelvin a title given to William Thomson, 1st Baron Kelvin a British mathematical physicist and engineer and Charles Darwin an English naturalist and geologist.
The Age of Enlightenment was at hand and Copernicus and Galileo had explained that the Sun was the center of our universe and Isaac Newton explained gravity, but being a very religious man Newton was still using the Bible to explain creation. People in these times actually studied nature through the scriptures, holding the Bible in one hand and their scientific instruments in the other. In these times the Bible still ruled the Earth and people thought that the age of our Earth could be determined by analyzing Biblical stories.
Buffon took on an enormous project trying to amass all the knowledge of what man knew about the natural world. While writing his encyclopedia, Buffon tried to explain all of the facts that he attained with overarching theories about the planet and its inhabitants, knowing that in order for him to locate the key to understanding Earth’s history, he should not rely solely on the Bible to be the only guide. Buffon proposed that a comet struck our Sun, which caused debris to be broken off that eventually formed into our planets. He said that initially, the Earth was scorching hot, but it gradually cooled until the molten rock turned to dry land and clouds rained down to form oceans. Buffon estimated that this entire process took over 70,000 years. This was in disagreement with Biblical scholars like James Ussher, who considered the Earth to be fewer than 7,000 years old.
Fourier spent a lot of his time trying to understand how heat flows through a body from a hotter region to a cooler one. Joseph Fourier followed Buffon in doing research into geological history, concentrating his interest on the behavior of heat. Fourier understood through his calculations that a planet the size of Earth should not be as warm as it is, considering its distance from the Sun. Fourier did not have the technology to make the measurements needed to explore his hypothesis about our atmosphere, which he reasoned held warmed air, so it could act as some kind of insulating blanket.
Fourier did make some wrong assumptions, but he advanced our knowledge of heat more than any other person and this was all initiated from him trying to understand Earth’s interior heat and its effect on the climate and his observations of the way temperature varies with depth below the Earth’s surface. When talking about Fourier, it is difficult for me to not turn this into a mathematical discussion, but I don’t want to proceed in this direction. Fourier stated that the problem of planetary temperatures provided the main impetus for his formulation of the analytical theory of heat. He applied what we now call Fourier series to correctly predict that the diurnal (during the day) variation of temperature should decay rapidly with depth and the annual variation more slowly. The calculation also gives an estimate of the amount of heat that flows into and out of the surface from sunlight in the course of the diurnal and seasonal cycle, and thus provides an additional check on the importance of solar energy in determining the Earth’s surface temperature.
Darwin enters the picture with his theory of evolution, which was one of the greatest scientific advances of all time and he makes a crude estimate of Earth’s age to be several hundred million years old, which is based on geology. He suspected that this was a sufficiently long enough time period for the processes of natural selection to take place and produce the wide range of species that exist on Earth. Our Earth had become more ancient than anyone had ever thought. Darwin only intended to provide a rough estimate about the age of our Earth in order to emphasize his point of how long it would take for all the species to evolve, but this statement became the subject of much controversy at the end of the nineteenth century.
The main proponent to Darwin’s argument was Lord Kelvin the great physicist, who made major contributions to thermodynamics, formulating the second law of thermodynamics and establishing the absolute temperature (Kelvin) scale. Kelvin knew the temperature at which rock melts and it seemed reasonable for him to assume that life could not have been present at the time when the whole surface of the Earth was molten magma. He also knew from reviewing Fourier’s results concerning the temperature of the soil at certain depths that, while the temperature of the surface of the Earth undergoes wide daily and annual variations, the Sun’s influence diminishes rapidly once one heads more than a few hundred meters down into the ground.
Kelvin disputed Darwin’s estimate and argued that Earth was much younger. Thomson proceeded to calculate the age of the Sun, basing his estimate on gravity and he came up with a theory that showed the Sun to be younger than what Darwin had predicted the age of our Earth to be. His calculations ended up being way off base, because he lacked a fundamental understanding of how stars and our Sun actually worked. Darwin was disturbed by Kelvin’s conclusions, as this argument went against his Theory of Evolution. Kelvin’s mathematics were impeccable, but he had no clue what radioactivity was all about, and that Uranium deposits deep under the Earth’s mantle were responsible for heating the Earth from within.