The existence of a magnetic field beyond 3.5 billion years ago is still up for debate - Phys.org

1. The existence of a magnetic field beyond 3.5 billion years ago is still up for debate  Phys.org
2. Ancient Microscopic Mineral Excavation Deepens Mystery of the Origins of Earth’s Magnetic Field  SciTechDaily
3. Origins of Earth's magnetic field remain a mystery  MIT News
4. Academic showdown as boffins biff-baff over when Version 1.0 of Earth's magnetic core was released  The Register
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