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Look at a world map and the east coast of South America seems to fit into the west coast of Africa. Many people noticed. Alfred Wegener was the one who gathered the evidence, made a full scientific case, and defended it for the rest of his life against fierce criticism. This post covers what he proposed, the evidence he used, why it was rejected, how it was eventually confirmed, and a worked example on how slow plate motion adds up to an ocean. Continental drift is in the NCERT Class 11 geography book, Fundamentals of Physical Geography, if you take geography for CBSE.
Who was Alfred Wegener?
NASA's Earth Observatory has a detailed profile of Wegener. He was born in Berlin on 1 November 1880 and earned a doctorate in astronomy in 1904, then turned to meteorology. In 1906 he and his brother Kurt set a world endurance record by staying aloft in a balloon for more than 52 hours. The same year he joined a Danish expedition to north-east Greenland, the first of several trips that made him an expert in polar weather and ice.
In December 1910 he wrote to his future wife asking whether South America's east coast did not fit Africa's west coast "as if they had once been joined". The idea stayed with him.
What did he propose?
On 6 January 1912, at a meeting of the Geological Association in Frankfurt, Wegener rejected the popular idea that sunken land bridges had once linked the continents. Instead, he said, the continents themselves had moved. His book, The Origin of Continents and Oceans, came out in 1915. It went largely unnoticed outside Germany until the 1922 third edition was translated into several languages.
By then he argued that all the continents had once formed one supercontinent, Pangaea ("all lands"). The US Geological Survey summarises that he contended Pangaea began to split apart around 200 million years ago.
What evidence did he use?
Coastlines. The Atlantic coasts of Africa and South America fit like jigsaw pieces.
Fossils. Remains of the same land and freshwater species, such as the reptile Mesosaurus and the fern Glossopteris, appear on continents now separated by oceans.
Rocks. Mountain ranges and coal deposits line up across the join. He compared it to matching the torn edges of a newspaper and checking that the lines of print run on.
Ancient climates. With the climatologist Wladimir Köppen he plotted evidence of past ice ages. Glacial traces from about 280 million years ago are scattered across regions that are hot today, including some of the hottest deserts. On his reconstructed map, which joined Africa, Antarctica, Australia and India, they clustered around the South Pole.
Why did geologists reject it?
His weak point was the mechanism. The NCERT chapter explains that he suggested two forces: a "pole-fleeing" force from Earth's rotation, and a tidal force from the Moon and Sun. Most scholars considered these totally inadequate. Wegener knew it. In his last revision, in 1929, he wrote, as quoted by NASA, "The Newton of drift theory has not yet appeared." He was an outsider to geology too, and the Earth Observatory profile records that attacks often targeted him personally.
How was he shown to be right?
From the mid-1950s, studies of rock magnetism and the ocean floor convinced most scientists that continents do move. In 1963, Fred Vine and Drummond Matthews published Magnetic Anomalies Over Oceanic Ridges in Nature, one of the ocean-floor studies of this period. The Earth Observatory profile notes that rocks near mid-ocean ridges are always young, and older further away: new ocean floor forms at the ridges. The result was plate tectonics: Earth's outer shell is broken into plates that carry both continents and sea floor. The mechanism differs from Wegener's, but the Earth Observatory notes he had already discussed convection currents in the mantle, the leading explanation today, in his 1929 revision.
Worked example: how far does 2.5 cm a year take a continent?
The USGS gives the average spreading rate of the Mid-Atlantic Ridge as about 2.5 cm per year, or 25 km in a million years.
Convert to kilometres: 2.5 cm = 2.5 × 10^-5 km.
Per million years: 2.5 × 10^-5 km × 10^6 = 25 km. That matches the USGS figure.
Over 180 million years: 25 km × 180 = 4,500 km.
That is the scale of the Atlantic: thousands of kilometres from a speed you would never notice in a lifetime.
Common mistakes: dropping a power of ten when converting cm to km (there are 10^5 cm in a km), and mixing "per year" with "per million years".
How did his story end?
In 1930 Wegener led a Greenland expedition. On 1 November, his 50th birthday, he left the mid-ice station Eismitte with the Greenlander Rasmus Villumsen to return to the coast. Searchers found Wegener's body on 12 May 1931. Villumsen was never found.
What can a student take from his way of working?
Borrow from other fields. A meteorologist used geology, palaeontology and climate data together.
Separate the pattern from the explanation. His pattern was right; his mechanism was not. Both can be true at once.
Say what you cannot yet explain. His admission that drift's Newton had not appeared was honest science.
Another scientist who rewrote how we read Earth's history is Charles Lyell. Slow processes that add up over vast times are hard to picture; the Fermi Simulation Lab has interactive simulations for ideas that are easier to see than to read.
Next step: look up how wide the Atlantic is at your chosen latitude, divide by 25 km per million years, and compare your answer with 200 million years.
