This review synthesizes evidence on Earth's geomagnetic field history and discusses how early establishment of the field (at least 4.2 billion years ago, inferred from zircon magnetism) may have supported planetary habitability via radiation shielding and water preservation. It highlights a proposed near-collapse of the dynamo near the end of the Precambrian and subsequent renewal in the earliest Cambrian, with potential implications for atmospheric escape and oxygenation. The paper frames several links to biological evolution (including Ediacara fauna) as possible and in some cases debated.