Who Built Ohio's Serpent Mound?

The Serpent Mound, a vast effigy built on a meteorite crater's edge in what's now Ohio, may be 900 years old -- or much older. Learn what we know and don't know in this episode of BrainStuff, based on this article: https://science.howstuffworks.com/environmental/earth/archaeology/ohio-serpent-mound.htm

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