Archive for May, 2010

Mineral evolution: Kelvin vs. Hutton

May 8, 2010

Blue gem mineral

A couple of weeks ago the very prolific Callan Bentley at Mountain Beltway raised some speculative questions inspired by the concept of mineral evolution, the idea that the mineral suite of the Earth has changed over time. I’ve been mulling over this proposition since, more or less in the back of my mind as more pressing personal happenings have been going on.

First, there is a terminological issue. The word “evolution” has meant very different things to different people over the centuries. Like most, if not all words, you cannot be assured that the etymological roots are anything other than a guide to the history. In today’s world, the word automatically brings up the name Darwin, even though it meant very different things to Erasmus than it did to his grandson Charles, who used it only sparingly.

Taken as its roots imply-unfolding in time-, the concept of mineral evolution would follow directly from logic of thermodynamics and an expanding Universe. Particular minerals, such as the one shown above, will form in environments wherein they are stable, or at least closer to equilibrium than whatever was there before. The parameters of the environment, as far as minerals are concerned, are temperature, pressure and composition. Consequently, in a Universe where energy is constantly dissipating, temperatures will constantly fall, and new, conceivably unique patterns of temperature, pressure and composition come and go. Predictably then, mineral suites will  change with time, with or without life!

Which takes me to Kelvin.

Geologists typically know Kelvin in the context of the age of the Earth debate. Geochemists and others whose curriculum involves thermodynamics know that aspect of his work: entropy, Kelvin scale, so forth. Never the twain should meet! But, in fact, they do. Albritton, in his book The Abyss of Time points out that the late 19th century debate between Kelvin and the geologists centered not so much on the age of the Earth as on the nature of geologic history. Kelvin’s  argument was not with Darwin the geologist, but through Lyell, with Hutton and his memorable phrase “no vestige of a beginning…” that we have all read, somewhat uncomprehendingly.

We read Hutton with difficulty, but not because of his writing style. You can check it out for yourself ( Theory of the Earth)   . What makes him difficult to understand is that he was writing in a thoroughly Aritotelian frame of reference that has eternalism at its base. Furthermore, he had no chemical atomic theory, no way to distinguish between fire, heat and phlogiston. No oxygen in his vocabulary. What he did have was the awesome ghost of Newton and the image of an eternally revolving system of Sun and planets. In short, at least according to historians of Geology like Martin Rudwick (Worlds Before Adam), no sense of geologic history as a series of unique events unfolding in a unique, non-repeating sequence.  This was the Huttonian foundation for Lyell’s cyclical uniformatarianism which made such difficulties for his admirer, Charles Darwin.

The mineral at the top of this page illustrates mineral evolution in the sense that it almost doesn’t exist. The conditions of temperature, pressure and composition that it requires are rarely achieved in the Earth, so it occurs in only one or two places on Earth. Fortunately for me, few people prize it as much as I do, so the price for this small example was within my wife’s birthday budget for me when I turned 65. I wore it as an ear stud until she passed.