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Dec 16 2009

The age of the Earth-10: The revolutionary impact of the discovery of radioactivity

(My latest book God vs. Darwin: The War Between Evolution and Creationism in the Classroom has just been released and is now available through the usual outlets. You can order it from Amazon, Barnes and Noble, the publishers Rowman & Littlefield, and also through your local bookstores. For more on the book, see here. You can also listen to the podcast of the interview on WCPN 90.3 about the book.)

For previous posts in this series on the age of the Earth, see here.

The dawn of the 20th century was an extraordinary time of ferment in science. In the case of physics, in addition to the turmoil over the age of the Earth, there was also the well-known crisis that the newly emerging models of the atom as a tiny positively charged nucleus and orbiting negative charges seemed to contradict the well-established theory of electrodynamics. Another crisis was that the ‘luminiferous ether’, the material believed to permeate all space and the carrier of light waves, seemed to be extraordinarily successful in evading all attempts at detecting its presence or its properties. In addition, the blackbody radiation spectrum seemed to defy understanding on the basis of what were thought to be well-established laws of mechanics and radiation.

But that same period also produced one major scientific revolution after another. 1900 saw the re-discovery of Mendel’s theory of genetics that showed that the heritable qualities we had were stored in our bodies in discrete units that were passed on intact to our progeny, and not blended away on breeding as previously thought, thus removing one major objection to natural selection. The full integration of Mendelian genetics with natural selection into what is now known as the neo-Darwinian synthesis was, however, not fully understood until around 1920, with the full flowering of the field of population genetics.

1900 also saw the introduction by Max Planck (1858-1947) of the quantum hypothesis that seemed to explain the blackbody radiation anomaly. 1905 saw the emergence of Albert Einstein (1879-1955) and his theory of relativity that made the ether redundant and dispensable, thus solving the mystery of why it had seemed so elusive. That year also saw the publication of a second paper by Einstein which contained the result that is now famously written as E=mc2. 1913 saw the introduction by Niels Bohr (1885-1962) of the planetary model of the atom, the first step in resolving the contradictions between the new atomic theory and electrodynamics.

But as far as the age of the Earth was concerned, the major discoveries that impacted it was the discovery of X-rays in 1895, followed rapidly by the discovery of the alpha, beta, and gamma radiation of radioactivity. There began a rush to isolate the elements that produced this extraordinary new radiation and to measure their properties. Marie (1867-1934) and Pierre (1859-1906) Curie were among the leaders of the quest in isolating these elements and soon the list contained actinium, uranium, polonium, thorium, and radium.

The key discovery that had relevance for the age of the Earth was the discovery in 1903 by Pierre Curie that radium emitted prodigiously large amounts of heat. An early calculation that same year showed that a mere 3.6 grams of radium per cubic meter would be sufficient to be the source of energy radiated by the Sun (Burchfield, p. 166). Since radium existed in the Earth, people immediately realized that if this heat did not have its origins in gravitational or mechanical or chemical energy (and it soon became clear that it did not and was instead due to the mass to energy conversion discovered by Einstein.), then this meant that there was a source of constant heat generation that had not been previously taken into account.

Since there was no way to determine how much heat was continually being produced in the deep interiors of the Earth by all the radioactive elements there, the old calculation methods of Kelvin and other physicists, who assumed that all the Earth’s heat was created at its formation and that the Earth could subsequently be treated as a strictly cooling body, had to be discarded. Furthermore, since there was no longer any method of determining the absolute age of the Earth, the desire of the geologists and paleontologist and natural selectionists for long ages could be accommodated. Too bad that Darwin did not live to see it.

But while radioactivity completely undermined the older methods for determining the age of the Earth, it at the same time gave birth to a new and far more accurate method.

It was Ernest Rutherford (later Lord Rayleigh, 1871-1937) who, with others, was associated with some of the key conceptual breakthroughs involving radioactivity, such as realizing that during radioactive decay, one element became transformed into another, which in turn was transformed into another, and so on until a stable element was reached, at which point the process stopped. He was the one who discovered that if you take a sample of radioactive material, the time taken for the initial amount of material to decay to half its original value was a fixed amount (known as its ‘half-life’) that is independent of the amount of material you started with.

So if you started with (say) 160 grams of some radioactive element that had a half-life of (say) 10 days, then after 10 days you would have 80 grams left, then after 20 days (i.e. another 10 days) you would have 40 grams left, after 30 days, you would have 20 grams left, and so on, with corresponding increases in the amount of the products created by the decay. What was to prove highly significant and useful was that each radioactive element had its own signature value of half-life and there was a huge range of half-lives for the different radioactive elements, ranging from fractions of seconds to hundreds of millions, even billions of years.

This discovery proved to be the key to finally unlocking the secret of the age of the Earth.

(Main sources for this series of posts are The Chronologers’ Quest: The Search for the Age of the Earth (2006) by Patrick Wyse Jackson and Lord Kelvin and the age of the Earth by Joe D. Burchfield (1975).)

POST SCRIPT: The Daily Show on Americans going to Mexico for health care.

<td style='padding:2px 1px 0px 5px;' colspan='2'American Refugees Seek Health Care in Mexico
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