Half a billion years ago, Earth was on track to become just like Mars. Ancient rocks now show what saved our magnetic field - ZME Science

Earth's magnetic field bounced back right in the nick of time around 550 million years ago.

A depiction of Earth, first without an inner core; second, with an inner core beginning to grow, around 550 million years ago; third, with an outermost and innermost inner core, around 450 million ye… [+5138 chars]

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