In the December issue of Focus, a science and technology magazine published by the BBC, Cherry Lewis answers the question of how we know the age of the Earth. Based on her book The Dating Game, she summarises the history of how we came to know the age of the Earth through the progressive development of radiometric dating methods.

When asked to provide a ‘key experiment’ that defined a turning point in this story, Lewis chose the one done by Arthur Holmes in 1911, which launched the discipline of geochronology. Holmes was only 21 when his article The Association of Lead with Uranium in Rock-Minerals, and Its Application to the Measurement of Geological Time, which detailed this work, was published by the Royal Society. The article includes the first-ever radiometric timescale, consisting of precisely seven dates.

While you need to subscribe to Focus in order to read the full article, you can glimpse it here by clicking on the magazine and turning the page seven times. Alternatively, you could go and buy a copy – it’s in your local newsagent now.