Scientists have discovered a mystery at the center of the Earth. The solid iron core of our planet is cooling faster on one side than the other, and nobody knows why.
The interior of Earth is arranged in layers. Moving downward from the surface, there’s the rocky crust and mantle, the liquid nickel-iron outer core, and the solid nickel-iron inner core.
Crushed under all the weight of the rest of the planet around it, the inner core experiences pressures over 3.5 million times stronger than the air pressure we experience here on the surface.
With this intense pressure comes intense heating. The temperature of the inner core is around 5,200°C — nearly as hot as the Sun’s surface.
As the solid core’s heat radiates outward, it is absorbed by the liquid outer core, which keeps the metal churning around and generating Earth’s protective geomagnetic field.
The reason for this appears to be the specific structure of the iron crystals in the core. As shown in the diagram above, they appear to be hexagonal, with the hexagons oriented along Earth’s axis of rotation.
At the same time, the heat lost from the core results in more iron solidifying around it, causing it to grow by about 1 millimeter every year.
However, a team of researchers, led by Dr. Daniel Frost, a seismologist at the University of California Berkeley, found that seismic waves behave very strangely as they pass through the inner core.
These seismic waves are generated by the numerous earthquakes that occur near the planet’s surface.
As the waves are picked up by various seismic monitors positioned around the world, the differences in how long it takes the waves from an earthquake to reach different monitors can tell us two things.
First, since these waves travel quickly through the crust, it allows seismologists to triangulate exactly where the earthquake took place.
Second, these waves also travel through the planet’s interior and move at different speeds depending on what kind of material they pass through. Thus, they can provide us with a reasonably accurate picture of the interior structure of Earth.
In a new study published in early June, they showed that waves traveling between the poles pass through the core faster than those traveling through from east to west.
The reason for this appears to be the specific structure of the iron crystals in the core. As shown in the diagram above, they appear to be hexagonal, with the hexagons oriented along Earth’s axis of rotation. However, this is unusual.
There’s no reason why they should take on this arrangement. After running highly detailed computer simulations of how Earth’s inner core grows, though, Frost and his team believe they have the answer.
The west side looks 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 we can explain that is by one side growing faster than the other.
This does not mean that the solid core is physically lopsided. The intense pull of gravity keeps the core spherical by redistributing the newly frozen iron crystals in the relatively ‘soft’ outer part of the inner core.
This does show that the core is apparently cooling faster on one side, underneath Indonesia, compared to the other side, which is under Brazil.
The Weather Network / ABC Flash Point News 2021.