The ‘demise’ of Kelvin

EPS-106, Nov. 4^th – 9^th, 1999

Lecture 13

Kelvin and the geologists were on a collision course. Lyell had argued that the Earth was very old – following the Uniformitarianistic arguments of Hutton. Kelvin’s estimates for the age of the Earth kept coming down. Eventually, Kelvin turned on the concept of uniformitarianism, saying that there wasn’t enough time. He was agreeable to the method of attempting reconstruction from the rock record and using the present as a key to the past. He was opposed to the idea that the agencies and forces have always operated at the same level of energy as today. If, as he contested, the laws of thermodynamics were obeyed, then the heat engine of the Earth must be changing with time.

It would be a very wonderful, but not an absolutely incredible result, that volcanic action has never been more violent on the whole than during the last two or three centuries: but it is as certain that there is now less volcanic energy in the whole earth than there was a thousand years ago, as it is that there is less gunpowder in the “Monitor” after she has been seen to discharge shot and shell, whether at a nearly equable rate or not, for five hours without receiving fresh supplies, than there was at the beginning of the action. Yet the truth has been ignored or denied by many of the leading geologists of the present day . . . Kelvin, 1864.

In 1868 he said that “a great reform in geological speculation seems now to have become necessary.” Hutton’s ‘no vestige of a beginning, no prospect of an end” must have drove Kelvin up the wall. He was no dummy, and all of his laws of thermodynamics were infallible. He was arguing with men who looked at rocks! He had to know that he was right. Why wouldn’t the geologists wise up and figure out what they were really seeing?

Thomas Henry Huxley responding to Kelvin’s attacks in a rebuttal given during his presidential address before the Geological Society of London. He pointed out that there are in fact three geological viewpoints:

1) Uniformitarianism, where there is no beginning or end, and unlimited time available.

2) Catastrophism, where there is limited time, but unlimited energy available for geological change

3) Evolutionism, the idea that there is a general consistency, but that over long periods of time, things have changed. This is probably the closest to what is accepted today. There was no oxygen in the atmosphere early on, but with time the planet evolved to have an O₂-atmosphere. Life has obviously changed through time.

As to Kelvin’s claim of 100 million years, Huxley asked, what about 200 million? 300 million? How well do we know it? He said:

Mathematics may be compared to a mill of exquisite workmanship, which grinds you stuff of any degree of fineness; but nevertheless, what you get out depends on what you put in; and as the grandest mill in the world will not extract wheat-flour from peascod, so pages of formulae will not get a definite result out of loose data

An arrogant, but brilliant mathematician, Peter Guthrie Tait, wrote in support of Kelvin. He extolled the virtues of mathematics and physics in removing the uniformitarian blinders from the eyes of the geologists and setting them back on the path to truth. A critic of Tait’s work wrote that Tait writes as though “thinking is forbidden, only calculation is permitted”.

What then happened is a group of geologists reinterpreted the strata in ways that were consistent with Kelvin. Finally Thomas Chrowder Chamberlain, professor of geology at the University of Chicago responded to Kelvin’s dogmatic approach. He said that he did not care for the “air of retrospective triumph” or the “tone of prophetic assurance” that permeated Kelvin’s addresses. He went so far as to say the following:

Is present knowledge relevant to the behavior of matter under such extraordinary conditions as obtain in the interior of the sun sufficiently exhaustive to warrant the assertion that no unrecognized sources of heat reside there? What the internal composition of the atoms may be is yet an open question. It is not improbable that they are complex organizations and the seats of enormous energies. Certainly, no careful chemist would affirm either that the atoms are really elementary or that there may not be locked up in them energies of the first order of magnitude. No cautious chemist would probably venture to assert that the component atomecules, to use a convenient phrase, may not have energies of rotation, revolution, position and be otherwise comparable in kind and proportion to those of a planetary system. Nor would he probably be prepared to affirm or deny that the extraordinary conditions which reside in the center of the sun may not set free a portion of this energy.

HOW PROPHETIC!!!

In 1896 Wilhelm Conrad Röntgen made his amazing discovery for which he later got a nobel prize in 1901. It all happened by accident. While working in his darkened shop, he was experimenting with the passage of electrical currents through a glass tube filled with gases at low pressure. He had covered the tube in black paper to prevent it from glowing and he just so happened to have a phosphorescent screen some one yard away from his cathode ray tube. Tthe room was dimmed and he was looking out of the corner of his eye (it turns out that you can see dim objects better out of the corner of your eye – try it sometime, on a dark night). So, what he saw was the phosphorescent compound glowing whenever he turned on his electrical current. He didn’t know what caused it, but called it X-rays. He went further and discovered that the X-rays passed through opaque material, for which medical technology is forever grateful.

Only one year later, in 1896, Henri Becquerel discovered radioactivity (or at least recognized some new form of energy. Becquerel, a French physicist, was the son and grandson of physicists. For three generations the Becquerel family had studied phosphorescence, or in other words, the ability for some substances to continue to glow after being exposed to light. After hearing about Röntgen’s results, Becquerel too began experimenting with X-rays. Becquerel chose to work with potassium uranyl sulfate, K₂UO₂(S)₄)₂, a salt of uraninium. He exposed it to sunlight and placed some photographic plates wrapped in black paper on it. When developed, the plates revealed an image of the uranium crystals. Becquerel concluded "that the phosphorescent substance in question emits radiation which penetrates paper opaque to light." Initially he believed that it was the sun's energy that was being absorbed by the uranium, which, in turn then emitted X-rays.

Further investigation, on the 26th and 27th of February, was delayed because the skies over Paris were overcast and the uranium-covered plates Becquerel intended to expose to the sun were returned to a drawer. On the first of March, he developed the photographic plates expecting only faint images to appear. To his surprise, the images were clear and strong. This meant that the uranium emitted radiation without an external source of energy such as the sun. Becquerel had discovered radioactivity, the spontaneous emission of radiation by a material. He himself stated to the French Academy of Sciences "There is an emission of rays without apparent cause. The sun has been excluded"

The compound that he used to investigate contained uranium, Becquerel found that the more uranium there was then the more intense the radiation was. From this, he concluded that uranium caused the radiation. He demonstrated that the radiation emitted by uranium were similar to X-rays but could be deflected by a magnetic field and therefore must consist of charged particles. Which meant that X-rays and "Becquerel rays" were two different things. Becquerel was awarded the 1903 Nobel Prize for physics for his discovery.

Marie Curie (only person – certainly the only woman – to have two universities named after her) began studies of natural substances and found that pitchblende, a natural uranium compound had more radioactivity than pure uranium. She concluded that there must be some other radioactive phase in the pitchblende. Along with husband Pierre, they isolated two new elements, radium and polonium. It was Marie Curie who coined the term “radioactivity”.

Ernest Rutherford then comes on the scene. Born in New Zealand, he arrived in Cambridge in 1895 for graduate studies and soon took up an interest in Röntgen’s and Becquerel’s work. He found that the emanations of uranium could be broken up into three parts. One was gamma rays, which were similar to X-rays, and are in fact, a form of electromagnetic radiation. Electromagnetic radiation is not affected by magnetic fields. But two other ‘particles’ were. They were deflected in opposite directions in a magnetic field, one had a positive change, the other negative. The negative charged particle turned out to be electrons, the positive turned out to be alpha particles, or helium nuclei.

Along with colleague Frederick Soddy, Rutherford derived his disintegration theory,

“the atoms of the radioactive bodies are unstable, and a certain fixed proportion of them become unstable every second and break up with explosive violence, accompanied in general by the expulsion of an a- or b-particle. The residue of the atom, in consequence of the loss of substance quite distinct in chemical and physical properties fromits parent”

Such a dramatic statement, that matter is not constant struck many conservative scientists as alchemy.

1903 – Pierre Currie discovers that compounds of radium constantly give off heat. Rutherford soon after realizes that the amount of heat is proportional to the amount of radioactive material, or the amount of a-particles they emit. This was big, big news for geology and the age of the Earth.

Rutherford in a article published in Harper’s Magazine:

The amount of heat emitted from radium is sufficient to melt more than its weight of ice per hour. The rate of heat emission is continuous and, so far as observation has gone, does not decrease appreciably with the time. In the course of a year, one pound of radium would emit as much heat as that obtained from the combustion of one hundred pounds of the best coal, but at the end of that time, the radium would apparently be unchanged and would itself give out heat at the old rate. It can be calculated with some confidence that, although the actual amount of heat per year to be derived from the radium must slowly decrease with the time, on an average it would emit heat at the above rate for about one thousanad years

He was wrong about the 1,000 years. It’s much more than that, but he had found an ‘unlimited’ supply of heat to combat Kelvin’s calculations.

Thus it does not appear improbable that the temperature gradient observed in the earth may be due to the heat liberated by the radioactive matter distributed throughout it. If this be the case, the present temperature gradient may have been sensibly constant for a long period of time, and Lord Kelvin’s computation may only supply the minimum limit to the age of the planet. thus the earth may have been at a temperature capable of supporting animal and vegetable life for a much longer time than estimated by Lord Kelvin from thermal data”

This is news of stunning proportion. It allows for a mechanism whereby the Earth could be hospitable to life for an unlimited amount of time. This helps Darwin, who ‘needed’ more time for his evolution to be correct. It also helps the poor geologists, who’s observations were pooh-poohed by the ‘smart’ physicists for so long. Interesting: The natural observations, both on life (natural selection) and in the rock record could not previously be reconciled with physics. This should have been a flag to the scientific community that something was wrong. But it took the discovery of radioactivity to bring it all together.

What did Kelvin think of this? Hogwash. He thought that Röntgen’s work was a hoax, and the heat ‘stored’ in a sample of radium given to him by Pierre Curie (which he carried around in his vest pocket) was actually stored there through conduction or radiation of external energy that ultimately races back to sources of gravitation.

Rutherford spoke before the Royal Institution in 1904. Kelvin was in the audience. Rutherford recounted later:

I came into the room, which was half dark, and presently spotted Lord Kelvin in the audience and realized that I was in for trouble at the last part of my speech dealing with the age of the earth, where my views conflicted with his. To my relief, Kelvin fell fast asleep, but as I came to the important point, I saw the old bird sit up, open an eye and cock a balefule glance at me! Then a sudden inspiration came, and I said Lord Kelvin had limited the age of the earth, provided no new source (of energy) was discovered. That prophetic utterance refers to what we are now considering tonight, radium! Behold! the old boy beamed upon me.

As T. Mellard Reade put it,

The bugbear of a narrow physical limit to geological time being got rid of, we are free to move in our own filed of science. The methods of geology have this advantage over pure physics, we can more readily appeal to nature for proof or disproof.

Radioactivity provided more than a source of heat. It also was a potential tool for dating the Earth. Rutherford recognized that the ratio of parent material (radioactive element) to the daughter stable compound is a function of time. For this to work, he needed to know the rate by which the decay had taken place and that the decay rate was constant. He had already found that temperature had no effect, so the method should work. In 1905, John William Strutt (later Fourth Baron Rayleigh) and discoverer of argon obtained an age of 2,000 million years on the basis of the helium content of a specimen containing radium. The same year, Bertram Boltwood, an American physical chemist, noted that lead was always associated with uranium ore, and concluded that the end product of uranium decay was lead. His age estimate was between 400 million and 2,200 million years.

In 1911, Arthur Holmes, working in Strutt’s laboratory at Imperial College compared the numerical ages from uranium-lead (U/Pb) ages with those estimated geologically. Carboniferous samples gave 340 million years, as compared to 370 for those of Devonian age rocks and 430 for Ordovician or Silurian age rocks. Specimens older than Cambrian gave from 1,025 to 1,640 million years. He stated that with further work, they could figure out the age of the earth and refine the dating of rocks of different ‘geological’ ages. He was 21 at the time.

In 1913, he wrote The Age of the Earth. He compared ages from salt contents of the ocean, geological, geothermal and astronomical ages with those from radioactivity. He concluded that there was a discrepancy. Either the decay rates were not constant, or the average rate of change produced by geological processes at present were not constant through time. He preferred the later explanation.

His estimates in 1937 are as follows:

	1937	1947	1960	1999
Cenozoic	68	58-68	68-72	65
Cretaceous	108	127-140	130-140	142
Jurassic	145	152-167	175-185	206
Triassic	193	182-196	220-230	248
Permian	227	203-220	265-275	288
Carboniferous	275	255-275	345-355	352
Devonian	313	313-318	390-410	412
Silurian	341	350	430-450	441
Ordovician	392	430	485-515	488
Cambrian	470	510	580-620	540

Get your free time chart at http://www.geosociety.org/pubs/timescl.htm

Not bad, considering that his methods were crude by modern standards and he was not aware of the fact that there were two types of uranium, indistinguishable chemically, which had different decay rates. This was recognized by Frederick Soddy, who named the different types isotopes.

In 1931, the game was over. A committee of geologists, paleontologists, physicists, and astronomers working under the auspices of the U.S. National Academy of Sciences wrote a report that put an end to the concept of an abbreviated age of the earth.

Charles Schuchert was given the task of determining the age of the earth from sedimentological records. He started from scratch and figured out the maximum thickness of the Cambrian strata, the Ordovician, etc. He came up with a sedimentological thickness of 259,000 feet. He combined it with maximum thicknesses in Europe and came up with 308,000 feet. Then he added some more to make sure he wasn’t missing anything and got up to 400,000 feet. Then, making allowances for gaps in the sedimentation rates he concluded that of the 500 million years since the beginning of the Cambrian, 60 should be allotted to the Cenozoic, 120 to the Mesozoic and 320 to the Paleozoic.

In conclusion, the writer will admit that he is surprised over his own results, for he started with the ideas that he could not find enough thickness of strata or enough breaks to meet the demands of time indicated by the radioactive minerals. He has, however, found easily enough marine strata since the beginning of Paleozoic time to call for 500 million years. In his “Historical Geology,” 1924, he said . . . “that the earth since the beginning of the Archeozoic is probably at least 500 million years old.” And now we are willing to admit 500 million years alone back to the beginning of Paleozoic time. One stratigrapher at least has wholly gone over into the camp of the radioactive workers!

From: The age of the earth / by the Subsidiary Committee on the Age of the Earth, Division of Physical Sciences with the cooperation of Division of Geology and Geography and American Geophysical Union, National Research Council: QE508 .N3 available through interlibrary loan at New Mexico Tech.

The workers were not ‘radioactive’, but Schuchert joined them anyway! The shackles of Kelvin were forever removed!!!