The inner core of the earth is becoming one-sided, but why doesn’t it overturn?
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Combining these disciplines, scientists provide an important clue about what is happening a few miles under our feet. In a new study, they revealed how the inner core of the earth grows faster on one side than the other, which may help explain the age of the inner core and the intriguing history of the earth’s magnetic field.
In the 4.5 billion years of our planet’s history, the core of the earth was formed very early, in the first 200 million years. Gravity pulls the heavier iron to the center of the young planet, leaving rocks and silicate minerals to form the mantle and crust.
The formation of the earth trapped a lot of heat on this planet. The loss of these heat, and the heating caused by continuous radioactive decay, has promoted the evolution of our planet. The heat loss inside the earth promotes the violent flow of the outer core of liquid iron, thus forming the earth’s magnetic field. At the same time, the cooling of the deep interior of the earth helps to promote plate tectonics, thereby shaping the surface of our planet.
As the earth gradually cools, the temperature in the center of the earth eventually drops below the melting point of iron under extreme pressure, and the inner core begins to crystallize. Today, the inner core continues to grow at a radius of approximately 1 mm per year, which is equivalent to solidification of 8,000 tons of molten iron per second. After billions of years, this cooling will eventually cause the entire core to become solid, causing the earth to lose its protective magnetic field.
People might think that this kind of solidification will form a uniform solid sphere, but this is not the case. In the 1990s, scientists realized that the speed of seismic waves passing through the inner core changed unexpectedly. This shows that some asymmetric changes are taking place in the kernel. Specifically, the eastern and western halves of the inner core show different seismic wave velocity changes. The eastern part of the inner core is under Asia, the Indian Ocean, and the Western Pacific, while the western part is under the Americas, the Atlantic, and the Eastern Pacific.
New research explores this mystery , Using new seismic observations, combined with geodynamic models and estimates of the behavior of ferroalloys under high pressure. They found that the eastern inner core below the Banda Sea in Indonesia grew faster than the western side below Brazil.
You can think of this uneven growth as making ice cream in a freezer that only works on one side: ice crystals only form on the side where the ice cream cools effectively. On the earth, uneven growth is caused by other parts of the earth absorbing heat from certain parts of the inner core faster than other parts.
But unlike ice cream, the solid core is subject to gravity, and new growth is evenly distributed through the peristaltic internal flow process, thereby maintaining the spherical shape of the core. This means that the earth is not in danger of overturning, although this uneven growth is recorded in the seismic wave velocity of our planet’s inner core.
So, does this method help us understand how old the kernel may be? When the researchers matched their seismic observations with their flow model, they found that the inner core–located in the center of the entire core, formed much earlier–probably between 500 million and 1.5 billion years. .
The study reports that the younger end of this age range is a better match, although the older end matches the estimate made by measuring changes in the earth’s magnetic field. No matter which number is correct, it is obvious that the inner core is a relatively young guy, about one-ninth to one-third the age of the earth itself.
This new work proposes a new model of the Earth’s inner core. However, some physical assumptions made by the author must be true for this to be correct. For example, the model is only valid when the inner core is composed of a specific iron crystalline phase, and there are some uncertainties about this.
So does our uneven inner core make the earth unusual? It turns out that many planetary bodies have two halves, and they are somewhat different from each other. On Mars, the northern half of the surface is lower, while the southern half is more mountainous. The crust on the near side of the moon is chemically different from the crust on the far side. On Mercury and Jupiter, the uneven surface is not the surface, but the magnetic field. It does not form a mirror image between the north and the south.
Therefore, although the reasons for all these asymmetries are different, the Earth has done a good job. In a solar system composed of tilted celestial bodies, it is just a slightly asymmetrical planet.