Clair Patterson was born in Mitchellville, Iowa in 1922 and died in California in 1995 at the age of 73.
He never won a Nobel Prize nor received the recognition that he justifiably deserved. However, he was one of the great experimental scientists of the 20th century.
He answered one of the great questions of science: "How old is the Earth?"
This question has been debated since antiquity but science weighed in on the subject in the early 1700s. By then, enough was known about geological processes such as erosion and sedimentation that naturalists began to try to estimate the Earth's age.
One of the first was the French naturalist Benoit de Maillet. In an effort to avoid conflict with the Catholic Church, de Maillet published his work on the age of the Earth as a fictitious conversation between a missionary and an Indian sage, Telliamed.
Telliamed explained to the missionary that gradually falling sea levels meant that the Earth was at least 2 billion years old. Furthermore, that life had originated in the seas and that humans were descended from these early forms of life.
Of course, the fictitious sage Telliamed is just "de Maillet" backwards. But this simple ruse allowed publication of his theory without religious persecution.
During the 19th century, the debate began in earnest with the likes of Charles Lyell's "Principles of Geology" and Charles Darwin's "On the Origin of Species". Darwin estimated that the erosion occurring in the English landscape meant that the Earth must be at least 300 million years old.
Darwin was surprised when, in 1862, the physicist William Thomson (later Lord Kelvin) determined that the earth was between 20 and 100 million years old based on the rate of cooling of the planet with the answer being closer to 20 million years old.
Thomson's estimates did not take into account two important factors. The first is that the mantle is a hot, sticky, viscous liquid. Magma does not behave like rock. His premise that the Earth had started at 2000 C and cooled in the same way as surface rocks was flawed.
The second stems from the discovery of radioactivity in 1894 by Henri Becquerel. Radioactivity existed before 1894 but Thomson and others trying to do calculations were not aware of its existence. They did not take the heat generated by radioactive elements into account.
As an example, elemental Radium is so hot that a given mass will melt an equivalent mass of ice in just one hour. This radioactive heat throws off the cooling curve that Thomson used for his calculation.
Radioactivity, though, provided an avenue to determine exactly how old the Earth is. Once radioactivity had been discovered, Becquerel, Pierre and Marie Curie, Ernest Rutherford, and many others devoted their scientific careers to understanding the process.
It was quickly determined that radioactive series existed with a predictable pattern of elements and isotopes arising. For example, Uranium-238 - which is the most abundant isotope of uranium - converts to Thorium-234 by alpha particle emission which in turn generates Protactinium-234 and Uranium-234 by releasing beta particles. U-234 then converts to Th-230, Ra-226, and so on until the radioactive decay finally concludes with Lead-206.
Since each radioactive decay occurs through a first order process, the half-life for the reactions is a measureable constant. A radioactive half-life represents the time it takes for one half of the mass of an element to decay to the corresponding daughter isotope. By knowing how much of each isotope is present, it is simple arithmetic to work backwards and determine how old the decay series is.
Uranium-235 leads to a different radioactive series but ultimately generates lead as the final product. However, in this case, it is Pb-207 and not Pb-206.
By using the relative abundance of different isotopes in specific rock samples, scientists were able to get a better handle on the age of the Earth. Further, by measuring Helium levels, they were able to provide a secondary measure of radioactivity as alpha-particles pick up electrons to become helium.
It was Clair Patterson that developed superior techniques for measuring lead concentrations in minerals and determining isotopic abundances. In collaboration with George Tilton, he developed a lead-lead dating system that could accurately measure the age of rocks on Earth.
Unfortunately, the Earth's crust is constantly shifting and rocks that were once near the surface are melted in the hot core while volcanic eruptions bring the elements to the surface again. There are very few places to measure the age of the planet on Earth.
However, by using a combination of the few rocks on the planet that date back to the beginning and by meteorites Patterson was able to definitively determine the age of the Earth as 4.553 billion years old with an error of only plus or minus 20 million years.
