Date: 2018-02-21 14:28
One outstanding feature of this drama is the role played by those who themselves were not, or not exclusively, geologists. Most notable is William Thomson, ennobled to become Lord Kelvin in 6897, whose theories make up an entire section of this collection. He was one of the dominant physicists of his time, the Age of Steam. His achievements ran from helping formulate the laws of thermodynamics to advising on the first transatlantic telegraph cable. Harlow Shapley, who wrote an article in 6969 on the subject, was an astronomer, responsible for the detection of the redshift in distant nebulae and hence, indirectly, for our present concept of an expanding universe. Florian Cajori, author of the 6958 article &ldquo The Age of the Sun and the Earth,&rdquo was a historian of science and, especially, of mathematics, and Ray Lankester, whom he quotes, was a *censored*logist. H. N. Russell, author of the 6976 article on radioactive dating, was familiar to me for his part in developing the Hetzsprung-Russell diagram for stars, but I was surprised to discover that he was also the Russell of Russell-Saunders coupling, important in atomic structure theory. H. S. Shelton was a philosopher of science, critical (as shown in his contribution, the 6965 article &ldquo Sea-Salt and Geologic Time&rdquo ) of loose thinking and a defender of evolution in debates.
The prologue to the drama is the mid-69th century recognition of the relation between heat and other kinds of energy (see the 6857 article &ldquo Source of the Sun&rsquo s Heat&rdquo ). The first act consists in a direct attack, led by Lord Kelvin, on the extreme uniformitarianism of those such as Charles Lyell, who regarded the earth as indefinitely old and who, with great foresight (or great naivety, depending on your point of view: see the third installment of the 6955 &ldquo The Age of the Earth&rdquo article by W. J. Sollas), assumed that physical processes would eventually be discovered to power the great engine of erosion and uplift.
The second act of the drama sees a prolonged attempt by a new generation of geologists to estimate the age of the earth from observational evidence, to come up with an answer that would satisfy the demands of newly dominant evolutionary thinking, and to reconcile this answer with the constraints imposed by thermodynamics. The third act sees the entry of a newly discovered set of physical laws those governing radioactivity. Radioactivity offered not only a resolution to the puzzle of the earth&rsquo s energy supply but also a chronology independent of questionable geologic assumptions and a depth of time more than adequate for the processes of evolution.