A new book excerpt published by Live Science revisits a 19th-century fight over the age of the Earth, when physicists used thermodynamics to challenge older assumptions and still got the number badly wrong. In the 1950s, American geochemist Clair Patterson used lead isotopes in the Canyon Diablo meteorite, found in Arizona in 1891, to date Earth at about 4.55 billion years, a figure now widely accepted. Long before that, physicist Christophe Galfard writes in "This Is Life: A Journey from Inside Your Body to Beyond Earth," published in 2026 by the University of Chicago Press and Picador, heat itself became the key to arguing that the planet was far older than the thousands of years many people had assumed.
Thermodynamics, a science of how heat moves, emerged from 19th-century work on steam engines, notably a book published in 1824 by the young French physicist Nicolas Léonard Sadi Carnot. If scientists could guess how hot Earth was at birth, they hoped, they could calculate how long it had taken to cool to its present temperature. British physicist William Thomson, later Lord Kelvin, made the most famous attempt. He pictured the planet as a smooth, solid ball of more or less the same material from surface to core, with no oceans or mountains, and calculated how long it would take to cool from red hot. He first said Earth was between 40 million and 400 million years old, then 100 million, then 40 million again. The estimates do not match the true age, Galfard writes, but they were treated as authoritative anyway. By the end of the century Thomson was Lord Kelvin, a scientific superstar "who had the power to undo, in a snap of fingers, the career of anyone who disagreed with him."
Geologists, Galfard says, mostly did not challenge him. Many thought geology was a matter of intuition, not "mathematical gibberish." Kelvin's former student John Perry thought something had been overlooked and told his mentor, then published in Nature, and was ignored by Kelvin and by the wider community. Perry did not treat the planet as uniform. He modelled a metallic core, a solid crust, and a mantle in between that, over long periods, behaved like a very slow liquid, with hot material rising and cooler material sinking in convection loops, like water in a heated pan. That picture, Galfard argues, was a more correct way to estimate the planet's age and pointed toward the engine of continental drift. It would have saved time, he writes, had anyone taken it seriously.
The excerpt is a historical argument, not a new dating study. Patterson's mid-20th-century isotopic work, not Kelvin's cooling calculation, is what set the modern age. The verified story is a fresh retelling of how a powerful physicist's elegant, oversimplified model drowned out a better one for years, and how the planet turned out to be far older than 40 million years.