Because it was one
Why Does the Map Look Like a Jigsaw?
The continents fit together because they were once joined and have been drifting apart ever since.
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Step 1 of 5
The fit is far too good to be chance.
South America's east coast matches Africa's west coast closely, and the match is better still using the true edge of the continental shelf.
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Step 2 of 5
The rocks and fossils match across the gap.
Identical rock formations and identical fossil species appear on both coasts, of animals that could never have crossed an ocean.
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Step 3 of 5
The surface is broken into moving plates.
Earth's rigid outer shell is cracked into large pieces that float on hotter, slowly flowing rock and creep a few centimetres a year.
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Step 4 of 5
New sea floor is being made between them.
Molten rock rises along a ridge down the middle of the Atlantic, hardens, and pushes the two sides steadily further apart.
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Step 5 of 5
Centimetres a year adds up enormously.
A few centimetres annually becomes thousands of kilometres over a hundred million years, which is how an entire ocean opened up.
The Atlantic widens about as fast as your fingernails grow, roughly 2.5 centimetres a year.
The short version
The continents fit together because they were genuinely joined, and new sea floor forming between them has pushed them apart ever since.
Try it yourself
Print a world map, cut out South America and Africa, and slide them together. The fit is startlingly good.
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