A mantle can mean a loose outer cloak or covering, or a layer that covers something, like the Earth’s mantle beneath the crust. It can also mean a role or responsibility that is passed from one person to another.
From Old French 'mantel', from Latin 'mantellum' meaning 'cloak' or 'covering'. The idea of a physical cloak expanded into a metaphorical covering or role.
When someone 'takes up the mantle', they’re literally putting on the cloak of responsibility. The Earth’s 'mantle' is named the same way: a thick layer wrapped around the planet’s core like a heavy coat.
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