Charles Darwin, Lord Kelvin, radioisotopes and the concept of time

When Charles Darwin published his famous volume The Origin of Species in 1859, he was met with howls of protest about many of its claims. One of the most revolutionary ideas in the book was the way in which it applied the concept of time to living beings by proposing that all the Earth’s populations of organisms were derived from a common ancestor, since when they had gradually developed into different forms and species. This concept of the gradual passing of time and its effect on life (also known as evolution) sparked huge philosophical and religious debates, as well as impregnating other disciplines such as geology. The slow evolution of living beings implied, among other things, that the Earth was much older than had previously been thought. However, William Thomson, the first Baron Kelvin, did not agree with Charles Darwin’s revolutionary ideas, and in order to refute them he used his renowned laws of thermodynamics to calculate that the true age of the Earth was between 20 and 40 million years. However, the discovery of radioactivity and radioisotopes in 1903 showed Lord Kelvin’s calculations to be incorrect, and demonstrated that the Earth was much older than had initially been calculated. Nowadays we know that the Earth’s age is 4.54*10^9 years (+/- 1%). But what is radioactivity? What role did radioactivity play in this dispute? How can radioactivity enable us to determine the age of things? What are the different methods of radiometric dating based on? Could it be possible that human beings have changed the environment to such an extent that we have altered the relations between certain radioisotopes? Can radioactive particles be seen?

Cycle: SCIENCE ON MONDAY: Earth sciences in our everyday lives

Organized by: Residència d’Investigadors, CSIC-Delegación en Cataluña, Institut de Ciències de la Terra - Jaume Almera