The matching shapes of the coastlines of West Africa and eastern South America have attracted attention since the first maps of the Atlantic. The German polar scientist Alfred Wegener took the idea further, publishing in 1912 many lines of evidence that continents now separated by oceans were once together. His mixture of plausible and unrealistic data was not taken seriously, especially because of the lack of a mechanism by which continents could plough through the solid rock of the ocean floors. By the early 1960s, some scientists were reconsidering the idea, notably Arthur HolmesArthur Holmes (1890–1965) Ernest Rutherford pioneered the use of radioactivity to determine the age of rocks; Arthur Holmes refined the method and developed it into a geological timescale, pushing back the age of the Earth to more than four thousand million years by the 1940s. He was especially interested in mantle convection and expanded on his ideas in his textbook Principles of Physical Geology. This wide-ranging textbook, first published in 1944 with a second edition in 1965, influenced generations of Earth scientists, including McKenzie. He read it as an undergraduate and enthusiastically told his mother, a landscape architect, about it. She was reading the book, but decided it was too heavy to take to bed, so she cut it up into manageable sections. “I was outraged,” says McKenzie. “I made her buy me a replacement copy.” .