In new work published in JGR: Solid Earth, researchers sampled lava flows from around Mount Erebus in Antarctica. They then analyzed the magnetic properties of the rocks to understand the paleomagnetic field changes in the past.

Here’s how that is possible: when rocks cool, the minerals in the rocks form crystals, and if those minerals contain iron, which basaltic lava such as that in Antarctica or Hawaii or the mid-Atlantic ridge does, those crystals align themselves with the Earth’s magnetic field. Just like the needle on a compass. And we can then analyze the age of the rocks using radiometric dating like we talked about last week and figure out which direction the magnetic field’s north pole was from the rocks.

We have to do a little backtracking because, of course, plate tectonics are a thing and continents move around, but we have a pretty good record of the rocks in the Atlantic Ocean, which don’t move that much. All of this information can now be combined into a history of our magnetic field.

The new paper, however, shows that the direction of the poles is all we can really extrapolate from all that data. It doesn’t tell us anything about how the field was shaped otherwise. To understand the shape of the magnetic field, the researchers plan to sample more rocks from more locations and attempt to put together a complete picture of the paleohistory of our magnetic field, looking at intensity as well as direction.

More Information

Eos article

“Four‐Dimensional Paleomagnetic Dataset: Plio‐Pleistocene Paleodirection and Paleointensity Results From the Erebus Volcanic Province, Antarctica,” H. Asefaw et al., 2020 December 4, JGR Solid Earth