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xkcd #3135: Sea Level
(imgs.xkcd.com)
Title text:
They're up there with coral islands, lightning, and caterpillars turning into butterflies.
Transcript:
Transcript will show once it’s been added to explainxkcd.com
Source: https://xkcd.com/3135/
Look at one spot and see how it repeats. Like the tides between South America and Africa kind of rotates through the Atlantic.