Читать книгу Professional Hairstyling - Joel Levy - Страница 13

To many at the time, such immense numbers seemed equivalent to eternity, and Lyell and, by extension, Darwin were seen as the standard-bearers of a school of geological thought called uniformitarianism. In its most extreme form, the uniformitarian view was that the Earth had effectively existed forever, and might well continue to do so, its geological processes endlessly cycling through the creation and destruction of landscape features. Lyell and Darwin did not subscribe to this extreme view, but they nonetheless became targets of the ire of a man who had proved that this theory of a never-ending cycle was impossible.

William Thomson, elevated to the peerage as Baron Kelvin of Largs in 1892 (the first scientist to be so honoured) and hence conventionally referred to as ‘Lord Kelvin’ or ‘Kelvin’, had elucidated, among other achievements, the laws of thermodynamics. Briefly stated, these meant that new energy could not be created out of nothing, and that the energy of any system would tend to dissipate. The laws meant that a perpetual-motion machine was impossible, and the endlessly recycling and eternal Earth of the extreme uniformitarians was effectively just that. Kelvin was having none of it.

Chronological confusions. A cartoon from the satirical magazine Punch, from 1869, lampooning the use of the Bible as a basis for determining the age of the Earth.

In March 1862, Kelvin published a paper, ‘On the age of the sun’s heat’, in which he calculated that the Sun had been burning for less than a million years. ‘What then,’ he asked, ‘are we to think of such geological estimates as 300,000,000 years for the “denudation of the Weald”?’ Given that his estimate of the age of the Sun, though imprecise, was based on ‘known physical laws’ and was orders of magnitude less than the figure arrived at by Darwin, he suggested that it was probable that the naturalist had underestimated the speed of erosion that could be caused by ‘a stormy sea, with possibly channel tides of extreme violence’.

Kelvin was one of the world’s great authorities on the dynamics of heat. He started with several assumptions: that the Earth had begun as a ball of molten rock; that, in accordance with his laws of thermodynamics, no heat could have been added to the system since this formation; and that convection currents had allowed uniform cooling of this molten globe to a solid sphere of uniform temperature, which then radiated the rest of its heat out into space from its surface. It was widely known from mining that the ground got hotter as you went down, with a thermal gradient of about 1°F per 50 feet (0.5°C per 15 metres). Kelvin did his own experiments to determine the thermal conductivity of rocks, and employed his mastery of Fourier mathematics to work out how long it must have taken for the planet to cool to its current temperature. He arrived at an estimate of 98 million years, with a range of 20–400 million years for the highest and lowest possible figures.