Earth’s magnetic field is life’s great protector – without it, our atmosphere would have long been stripped away by powerful solar winds. Despite its importance, there’s very little we know about it, but we do know that it has fluctuated and changed over the course of the last few billion years or so.
Writing in the journal Geophysical Research Letters, one particular scientist thinks that it used to be even more radically different than has previously been thought. Instead of having just a north and south pole, as it does today, this study raises the remarkable possibility that Earth may have once had multiple poles chaotically distributed all over the world.
Using a series of computer simulations that replicated the outflow of heat from the center to the fringes of our planet, starting from its fiery birth 4.5 billion years ago, the paper’s sole author notes that it’s incredibly unlikely our magnetic field was stable right from its inception. Instead, it remained very weak up until the formation of the solid iron core 650 million years ago, and only then did our classic, potent, two-pole (or “dipole”) magnetic field take shape.
“What I found was a surprising amount of variability,” Peter Driscoll, a researcher specializing in Earth’s magnetic field at the Carnegie Institution for Science, and author of the study, said in a statement. “These new models do not support the assumption of a stable dipole field at all times, contrary to what we'd previously believed.”
Earth didn't always have just a north and south magnetic pole. imagedb.com/Shutterstock
Our magnetic field is generated thanks to the motion of the metallic liquid outer core. Heat – both primordial leftover embers from the planet’s formation, and the radiogenic heat from unstable elements – escapes from the inner and outer core and makes its way to the surface. In doing so, massive convection currents are set up within the outer core, which moves huge amounts of nickel and iron around. It is this movement that generates the planet’s magnetic field.
The speed and power of these convection currents are directly related to how powerful and stable Earth’s magnetic field is. Some studies suggest that until the Earth’s solid inner core formed – a process known as the iron catastrophe – the convection currents were inefficient.
When the iron heart of the world froze into place, the outer core was left with less dense elements, and it could convect far more readily. This led to a strengthening of Earth’s magnetic field around 1 billion years ago, and this new study’s simulations appear to agree with this assessment.
According to Driscoll’s own 3D computer simulations, around this time in Earth’s history, we had multiple poles – several North, South, East and West poles, in fact – whereas beforehand and afterward, the world had a dipolar magnetic field. The only explanation is that the iron catastrophe initially caused huge fluctuations in the behavior of the liquid outer core, which caused the poles to “split” and the magnetic field to go haywire.
Eventually, around 650 million years ago according to this study, the solid iron core properly solidified, and the outer core calmed down a bit again. This brought Earth back into the dipolar regime. “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,” Driscoll noted.
Image in text: A sketch of the Earth's magnetic field lines from around 1 billion years ago. Peter Driscoll