https://www.scientificamerican.com/article/greenland-rocks-suggest-earths-magnetic-field-is-older-than-we-thought/

Magnetic minerals in ancient Greenlandic rocks suggest that Earth’s magnetic field arose at least 3.7 billion years ago. The finding pushes back the time of the magnetic field’s birth to about 200 million years earlier than the commonly accepted estimate—around the time life first appeared on Earth.

Scientists think that having a magnetic field makes Earth more hospitable to life. The field, which is generated by liquid iron sloshing about in the planet’s core, shields Earth from energetic particles flowing from the Sun. It helps the planet hold on to its atmosphere and maintain liquid water on its surface.