By now you should know this to be true: nothing in the world is permanent except change. It applies to everything, even the Earth’s magnetic poles. You read it right. If this is the first time you’re hearing about this, it’s really about time you knew that north wasn’t always north, and south wasn’t always south. In fact, if the setting of the HBO series ‘Game of Thrones’ was 41,000 years ago, Jon Snow wouldn’t be known as the new King of the North, he would be known as the new King of the South. You get the idea.
Now back to magnetic poles. As we were saying, just like everything else, the Earth’s magnetic poles flip from time to time. And the reversal can sometimes last for centuries or even millennia.
As evidenced by the alignment of observable magnetic minerals, we know for a fact that several magnetic reversals have already transpired throughout Earth’s history, with the last reversal – known as the Matuyama-Brunhes reversal. What we don’t know is why such magnetic reversals happen.
Scientists, though, have a few ideas on the cause of such reversal, all of which are based on the theory that the Earth’s magnetic field is generated by the motion of molten iron in the Earth’s outer core. When ‘something’ causes that movement to change, it results in magnetic pole switching. It’s that ‘something’ which scientists are trying to figure out.
According to Paula Koelemeijer — a Postdoctoral Fellow in Global Seismology from the University of Oxford — they might have stumbled on a plausible explanation: lava lamps. More specifically, the scientists discovered that areas above the Earth’s core could behave like ‘giant lava lamps’, with blobs of rock periodically going up and down deep within our planet, causing its magnetic field to flip.
To arrive at this theory, the research team turned to seismic signals generated by earthquakes as this was the only possible way to study the Earth’s core, considering how unimaginably deep it is. Apparently, measuring the oscillations caused by an earthquake, especially a large one, the data can be used as a basis to determine different structures that can be found within our planet.
By using this technique, the team was able to find out that at the top of the Earth’s core are two humongous regions — referred to as large-low-velocity-provinces or simply ‘blobs’ — where seismic waves travel more slowly compared with other surrounding regions. These blobs are thought to be less dense than other surrounding materials simply because they’re hotter. And being lighter causes them to rise up towards the surface, which is why they are found on top of the Earth’s core.
Now, an alternative theory has emerged. According to the scientists, it might be the chemical composition of the blobs (not their being less dense) that is making them behave like they do. Like ‘blobs in a lava lamp’, they heat up periodically and rise up to the surface, then cool down and drop back on the core.
If this turns out to be accurate, it would mean that this periodic rising and falling of the blobs can change the way heat is extracted from the Earth’s core. This could also explain why the Earth’s magnetic field occasionally flips. Following this line of thinking, the fact that our magnetic field has flipped more than once might also mean that over time, the internal structure of our planet may have changed several times as well.
Going forward, the team intends to use more data from the Earth’s oscillations so they can come up with a more detailed picture of the Earth’s core and better understand what’s going on deep within it. Hopefully, this can also provide us a more definitive idea on when our planet’s magnetic poles will flip so we can be better prepared for it, in case that happens within our lifetime that is.