Florian Cajori, author of the 1908 article “The Age of the Sun and the Earth,” was a historian of science and, especially, of mathematics, and Ray Lankester, whom he quotes, was a zoologist. 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 1900 “The Age of the Earth” article by W. Sollas), assumed that physical processes would eventually be discovered to power the great engine of erosion and uplift.
The most famous came in 1654, when Archbishop James Ussher of Ireland offered the date of 4004 B. Within decades observation began overtaking such thinking.
In the 1660s Nicolas Steno formulated our modern concepts of deposition of horizontal strata.
Nevertheless, by the late 19th century the geologists included here had reached a consensus for the age of the earth of around 100 million years.
Having come that far, they were initially quite reluctant to accept a further expansion of the geologic timescale by a factor of 10 or more.
The first argument was completely undermined after taking into account the amount of heat generated by radioactive decay.
The second depended on highly dubious theories of formation of the earth and moon and plays relatively little role in this compilation.The second referred to such topics as the detailed shape of the earth (bulging slightly at the equator) and the dynamics of the earth-moon system.The third referred to the heat of the sun, particularly the rate at which such heat is being lost, compared with the total amount of energy initially available.This position came to be known as uniformitarianism, but within it we must distinguish between uniformity of natural law (which nearly all of us would accept) and the increasingly questionable assumptions of uniformity of process, uniformity of rate and uniformity of outcome.That is the background to the intellectual drama being played out in this series of papers.Most notable is William Thomson, ennobled to become Lord Kelvin in 1892, whose theories make up an entire section of this collection.