Wegener was not a geologist; he worked in meteorology and polar exploration. In 1910, looking at an atlas, he noticed that the eastern coast of South America and the western coast of Africa matched. Over the next years he gathered supporting evidence: identical fossil reptiles in Brazil and West Africa; the Appalachian and Scottish mountain chains looking like the broken halves of a single range; the Permian Karoo coal and glacial deposits across India, Australia, Antarctica and South Africa making sense only when these continents were assembled into one.

His paper to the Geological Society of Frankfurt on 6 January 1912 and his 1915 book "The Origin of Continents and Oceans" argued that the supercontinent he named Pangaea had broken up roughly 200 million years ago. But Wegener could not explain the mechanism that moved the continents; he could only invoke vague "transport forces." Geologists of the day rightly found this inadequate — and the Anglo-Saxon academy in particular dismissed his hypothesis as "geological fantasy" for decades.

Wegener died on the Greenland ice cap in 1930, on a research expedition; he never saw his theory confirmed. When the ocean floor was mapped in the 1950s and 60s, the mid-ocean ridges were found to be producing new oceanic crust and the paleomagnetic stripes on either side were symmetric. By 1968 "plate tectonics" — Wegener's idea coupled with mantle convection — had become the unifying theory of modern earth science.

Continental motion today is measured directly by GPS: the Atlantic widens by about 2-3 centimetres a year, roughly the rate at which a fingernail grows. The formation and breakup of Pangaea appear on the Eon timeline as events of hundreds of millions of years ago; this moment in 1912 is the birth of the modern idea that made reading that deep past possible.