When seismic waves pass through the body of our planet, they appear to travel 3% faster when moving vertically from pole to pole than horizontally from east to west.
New models suggest this is because the Earth’s solid core is growing faster on one side, deep under the Banda Sea in Indonesia, and slower on the other side, under Brazil.
There was a time when our planet did not have a solid core. The deepest interior of our planet probably held a mass of molten material for billions of years before the liquid iron in the center began to cool and solidify.
This means that the very center of the Earth could be a giant, growing cluster of crystallized iron, and when those crystals line up in a certain way, it likely allows seismic waves to travel faster in certain directions.
While running models of how this particular alignment could have happened, the researchers came across an unexpected explanation: Earth’s inner core is developing in an unbalanced manner.
“The simpler model seemed a bit unusual – that the inner core was asymmetric,” says world seismologist Daniel Frost of the University of California at Berkeley.
“The west side is different from the east side all the way to the center, not just at the top of the inner core, as some have suggested. The only way to explain this is that one side grows faster than the other.”
It’s impossible to dig into the Earth’s inner core to verify what’s going on, so this is an area of ââresearch ripe for debate. Seismic wave propagation and computer simulations are some of the only ways we can test possible explanations for why our planet is formed as it is.
Using various computer models that take into account the geodynamics of the Earth and the physics of iron minerals under high pressure and temperature, researchers have now attempted to understand why the inner core of our planet is aligned in such a peculiar way. .
The simplest explanation they found was that our world’s crystal nucleus is growing fastest at its equator and on the east side in particular.
“This corresponds to a growth rate 40% lower at the poles and 130% higher at the equator compared to the world average”, conclude the authors.
“The growth rate at the equator varies between the eastern and western hemispheres from 100 percent to 160 percent of the global average rate, respectively.”
This asymmetric growth rate suggests that some parts of the Earth’s inner core are warmer, while others are cooler, allowing iron crystals to form faster. Gravity then distributes this excess growth evenly throughout the soft but solid core, keeping the overall spherical shape and driving the crystals towards the north and south poles.
Ultimately, the researchers explain, it is this gravity motion that aligns the crystal lattice of Earth’s inner core along our planet’s axis of rotation.
And so it has been from the very beginning. The model indicates that this type of asymmetric growth has occurred since the interior of the planet began to cool and solidify, with a radius growing more than one millimeter per year on average.
If the model is accurate and this is the true rate of growth, it means that the solid inner core of the Earth is a relatively recent phenomenon, only appearing to be between half a billion and 1, 5 billion years old, but probably on the younger side.
This is confusing because the Earth’s magnetic field is at least 3 billion years old, and this field is believed to form when the heat from the crystallization of iron in the inner core boils the molten material in the core. external.
If the Earth’s core is really that young, it could mean that our planet’s magnetic field has not always been generated in the same way.
Some scientists, for example, have suggested that the original magnetic field was much weaker than it is now, and that it was created by dissolved light elements, accumulating at the periphery of the inner core of our planet.
The researchers say it wasn’t until these elements started to crystallize that the magnetic field got stronger. The seismic waves propagating throughout the crystal nucleus then induced the electromagnetic field that we know today.
Even from the movements of tiny crystals deep in the core of our planet, great forces can develop.
The study was published in Geosciences of nature.