Earth may have developed a magnetic field as early as four billion years ago — more than half a billion years earlier than was thought.
John Tarduno at the University of Rochester in New York and his colleagues measured faint magnetic signals of iron-bearing minerals trapped inside zircon crystals up to four billion years old from the Jack Hills region of Western Australia. They found that the magnetic field fluctuated in strength, from a value similar to today's field (around 25 microteslas) to about 12% of that.
An ancient magnetic field when the planet was only about 500 million years old would have been a good, if imperfect, shield against the solar wind. This could have made the young planet more hospitable to life, the authors say.