What did Earth’s magnetic field used to look like?

In the distant past, Earth’s magnetic field was considerably different than it is today, and it likely originated from more than just two poles, according to a new study from Peter Driscoll, an Earth and planetary scientist from the Carnegie Institution for Science in Washington DC.

Writing in the latest edition of the journal Geophysical Research Letters, Driscoll investigated the affect that the solidification of the Earth’s core might have had on the magnetic field, using models of the planet’s thermal history to make a surprising discovery: the world which we call home did not necessarily have just a north pole and a south pole.

In fact, in a statement, he explained that he found “a surprising amount of variability” in these simulations, and that these models “do not support the assumption of a stable dipole field at all times, contrary to what we’d previously believed.” During solidification, Driscoll added, Earth may have shifted from a two-polar world to one in which the weaker magnetic field fluctuated wildly between different poles, and eventually back to the bipolar world we know today.

“These findings could offer an explanation for the bizarre fluctuations in magnetic field direction seen in the geologic record around 600 to 700 million years ago,” he said, pointing out that there would be “widespread implications for such dramatic field changes” during ancient times.

So how is this even possible, and what does it mean?

As Driscoll and the Carnegie Institution explained, Earth generates a powerful magnetic field that extends from its core out into space. This field helps protect the atmosphere, deflecting high-energy particles originating from the Sun and elsewhere in the solar system that would otherwise bombard the surface with cosmic radiation that could be harmful to living organisms.

The magnetic field is created by a phenomenon known as the geodynamo, which involves the motion of liquid iron in the outer core caused by heat loss and the solidification of the inner core. Yet the inner core was not always solid, which led to the question: what impact would the early solicitation of the inner core have had on the planet’s magnetic field?

In order to try and solve this problem, Driscoll created a model of the Earth’s thermal history that dates back 4.5 billion years. His models indicate that the inner core should have begun to solidify roughly 650 million years ago, so he conducted additional simulations to look for changes to the magnetic field during this time, and found that approximately 1 billion years ago, the planet may have shifted from a modern-looking magnetic field to one that was vastly different.

While the modern-type field would have been a “strong” magnetic field with opposing poles in the north and south, the transition would have caused it to become “weaker” and to experience a series of wild fluctuations in terms of intensity and direction, the Institution explained. During this time, the field would have originated from several different poles. Then, soon after the core is believed to have solidified, the simulations predict that magnetic field would have returned to a traditional “strong,” two-pole one.

“Overall, the findings have major implications for Earth’s thermal and magnetic history,” the Institution said, “particularly when it comes to how magnetic measurements are used to reconstruct continental motions and ancient climates. Driscoll’s modeling and simulations will have to be compared with future data gleaned from high quality magnetized rocks to assess the viability of the new hypothesis.”

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Image credit: Peter Driscoll, Carnegie Earth and Planetary Science

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