A research team led by John Tarduno of the University of Rochester in New York went to Australia’s Jack Hills and collected ancient samples of rock containing the crystallized mineral zircon. Once zircon cools below a certain temperature, roughly 1,085 degrees Fahrenheit, the iron-bearing minerals inside freeze in a tableau, like little soldiers aligned with the planet’s magnetic field. The older the crystals, the older the tableau, and the older the magnetic field.
Tarduno contends that the Jack Hills’ zircon is 4 billion years old, according to radioactive dating, and that nothing has unfrozen and rearranged its magnetic alignment since. That means the magnetic field is also at least that old and has swaddled Earth almost since the planet’s birth, just half a billion years before that.
The Magnetic Field Is (So Far) Just Very Old:
Another group, led by MIT’s Benjamin Weiss, collected rocks from the same area of the Jack Hills but says the zircon, although old, may not have been magnetized billions of years ago. Weiss’ team found that the rock conglomerate the zircon crystals were in had been magnetized just 1 billion years ago, when it probably formed as part of a volcanic eruption nearby. That means the zircon crystals within likely lost their former magnetic direction and recorded the magnetic field during the volcanic event that made the rock. That “remagnetization” would mean even if Earth’s magnetic field existed 4 billion years ago, there’s no evidence left to prove it.