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human
ELI5: How do we know Lucy skeleton is 3 million years old?

i understand that carbon dating can only estimate, and the estimated age can only go back 50,000 years (am i wrong about this??). so what other form of dating is used to determine Lucy living over 3 million years ago?
gpt
Carbon dating only goes back so far because eventually you run out of relatively short-lived carbon isotopes.

To accurately date older materials you can use longer-lived isotopes with much longer half-lives, and/or try to date the rock layer they were found in.

Lucy was dated by using argon isotope dating in the adjacent rock layer.