Lord Kelvin recalculates the age of planet Earth, including the (predominant) heat source due to the decay of the previously unknown radioactive elements it contains. The new calculation extends the Earth’s age from a few thousand years to several hundred million years (we now know it is 4.5 billion years). This argument thus supports Darwin’s theory. A few years earlier, in fact, Kelvin had used the Earth’s age as proof that Darwin’s theory must be wrong because there had not been time for species to evolve. Darwin died without knowing the true age of the Earth, and that his theory was indeed correct.
