By the middle of the nineteenth century most learned people thought the Earth was at least a few million years old, perhaps even some tens of millions of years old, but probably not more than that. So it came as a surprise when, in 1859 in On the Origin of Species, Charles Darwin announced that the geological processes that created the Weald, an area of southern England stretching across Kent, Surrey, and Sussex, had taken, by his calculations, 306,662,400 years to complete.

The assertion was remarkable partly for being so arrestingly specific but even more for flying in the face of accepted wisdom about the age of the Earth. Darwin loved an exact number. In a later work, he announced that the number of worms to be found in an average acre of English country soil was 53,767. It proved so contentious that Darwin withdrew it from the third edition of the book. The problem at its heart remained, however. Darwin and his geological friends needed the Earth to be old, but no one could figure out a way to make it so.