THE AGE OF THE EARTH

LORD KELVIN'S BRILLIANT ERROR

The 19th century debate in the scientific community of Europe between the evolutionists and those who accepted a literal interpretation of the Bible became centered on attempting to determine the age of the earth. The earth's age would be a scientific test of the principles of evolution as presented by Darwin, because all involved in the controversy recognized that the evolution of the great diversity of species on our planet would take time. Remember it was Hutton's recognition of great expanses of geologic time that gave Darwin the opportunity to consider evolution through natural selection. Unfortunately recognizing the importance of the age of the earth and determining it are two different problems. On the other hand, science of the late 19th century had time on its hands. All the major scientific problems had been solved, or at least they thought they had. So one of the most respected scientists of the time, Lord Kelvin, who had worked to establish the laws of thermodynamics, turned his attention to solving the problem. His approach was quite simple and quite brilliant. The age he determined, a few tens of million years at most, however,was wrong. His story provides important insights into the ways of science and potential pitfalls that await all of us who fail to recognize the difference between assumption and established fact.

I. Lord Kelvin's experiment

A. Theoretical basis

B. Methods

1. Heat flow in solids

2. Measuring the Geotherm

3. Extrapolating an age

II. The flawed assumptions

A. A new source of energy

B. Rates of heat flow -- conduction and convection

III. Absolute ages using radiogenic dating

A. Methods

B. Results

Objectives:

1. Discuss the significance of the age of the earth relative to the theory of evolution.

2. Discuss the assumptions (both accurate and inaccurate) made by Lord Kelvin in his determination of the earth's age.

3. Explain why convection in the earth's interior makes extrapolation of the near surface geotherm to the interior of the earth inaccurate.

4. Radioactivity proved Lord Kelvin wrong in two ways. Explain.

5. Use methods of radiogenic dating to solve sample age problems.

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