The Dating Game
Press release issued: 14 September 2007
Dating of the age of the Earth was one of the most important developments in geology, because it ultimately led us to understand how continents moved around the globe.
Dr Cherry Lewis from the University of Bristol will talk about the history of dating the age of the Earth at the BA Festival of Science in York on Thursday 13 September.
By the end of the 19th century, many geologists still believed the age of the Earth to be a few thousand years old, as indicated by the Bible, while others considered it to be around 100 million years old, in line with calculations made by Lord Kelvin, the most prestigious physicist of his day.
Dr Lewis said: “The age of the Earth was hugely important for people like Darwin who needed enormous amounts of time in which evolution could occur. As Thomas Huxley, Darwin’s chief advocate said: ‘Biology takes its time from Geology’.”
In 1898 Marie Curie discovered the phenomenon of radioactivity and by 1904 Ernest Rutherford, a physicist working in Britain, realised that the process of radioactive decay could be harnessed to date rocks.
It was against this background of dramatic and exciting scientific discoveries that a young Arthur Holmes (1890-1964) developed the technique of dating rocks using the uranium-lead method and from the age of his oldest rock discovered that the Earth was at least 1.6 billion years old (1,600 million).
But geologists were not as happy with the new results as, perhaps, they should have been. As Holmes put it: “the geologist who ten years ago was embarrassed by the shortness of time allowed to him for the evolution of the Earth’s crust, is still more embarrassed with the superabundance with which he is now confronted”. It continued to be hotly debated for decades.
Dr Lewis commented, “In the 1930s the age of the Earth crept up towards three billion years, but this meant it was older than the Universe, then calculated to be less than two billion years old. It was not until the 1950s that the age of the Universe was finally revised and put safely beyond the age of the Earth, which had at last reached its true age of 4.56 billion years. Physicists suddenly gained a new respect for geologists!”
In the 1920s the new theory that the continents were drifting around the globe became the great scientific conundrum, but most geologists were unable to accept the concept due to the lack of a mechanism for driving them. In 1928 Arthur Holmes showed how convection currents in the mantle could be this mechanism. This proved to be correct but it was another 40 years before his theories were accepted and the theory of plate tectonics became a reality.
The theory of plate tectonics has proved to be as important as the theory of evolution and the discovery of the structure of the atom, but without the discovery of how to quantify geologic time, confirmation of plate tectonics would not have been possible.
Today, few discussions in geology can occur without reference to geologic time and plate tectonics. They are both integral to our way of thinking about the world. Holmes died in 1964 having lived just long enough to see his ideas of continental drift confirmed.