Why does the Earth's core grow more on one side than the other |  international |  News

The Earth’s core formed very early in the 4.5 billion years of our planet’s history, in the first 200 million years.


Located more than 5,000 kilometers below us, the Earth’s solid, mineral inner core has not been discovered Until 1936. Nearly a century later, we still struggle to answer basic questions about when and how it was formed.

They are not easy puzzles to solve. We cannot directly sample the inner core, so the key to solving its mysteries lies in the cooperation between them seismologiststhat takes indirect samples with seismic waves, Geodynamictas, who make models of their dynamics, and Metal physicistswhich studies the behavior of iron alloys at high pressures and temperatures.

By bringing these disciplines together, scientists have provided an important clue to what is happening miles below us. employment New study, reveal how Earth’s inner core is growing faster than the other side, which may help explain the age of the inner core and the intriguing history of Earth’s magnetic field.

the beginning of the earth

Earth’s core has been formed thus In the 4.5 billion years of our planet’s history, in the first 200 million years. Gravity pulled the heavier iron toward the center of the young planet, leaving rocky minerals and silicate to form mantle and crust.

The formation of the Earth captured a lot of the heat inside the planet. The loss of this heat and the warming from continuous radioactive decay has led to the evolution of our planet ever since. The heat loss inside causes the strong flow into the outer liquid iron core, resulting in its formation Earth’s magnetic field. Meanwhile, deep cooling inside helps to enhance tectonic platesthat forms the surface of our planet.

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As the Earth cooled, the temperature at the center of the planet eventually dropped below the melting point of iron at extreme pressures, and the inner core began to crystallize. Today, the inner core continues to grow at a radius of about 1 mm each year, which is equivalent to the hardening of 8,000 tons of cast iron every second. Within billions of years, this cooling will eventually cause it all to happen The pulp becomes hard, leaving the Earth without its protective magnetic field.

The main problem

It can be assumed that this solidification creates a homogeneous solid sphere, but it does not. in the 1990s, Scientists They realized that the speed of seismic waves traveling through the inner core varies unexpectedly. This indicates that something asymmetric was going on in the inner core.

Specifically, the eastern and western halves of the inner core showed different differences in the velocity of seismic waves. The eastern part falls under Asia, the Indian Ocean, and the Western Pacific Ocean, and the western part is under America, the Atlantic Ocean, and the Eastern Pacific Ocean.}

The seismic waves suggested that the Earth’s solid iron core is asymmetric. Sanne Cottaar, author provided

The new study investigated this mystery, using new seismic observations combined with geodynamic models and estimates of how iron alloys behave under high pressure. They found that the eastern inland core under the Banda Sea in Indonesia is growing faster than the western core under Brazil.

This uneven growth is like making ice cream in a freezer that only works on one side – ice crystals form only on the side of the ice cream where refrigeration is effective. On Earth, the uneven growth is due to the rest of the planet absorbing heat more quickly in some parts of the inner core than in others.

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But, unlike ice cream, the hard inner core is subjected to gravitational forces that distribute the new growth evenly through a subtle inflow process, which maintains the spherical shape of the inner core. This means that the Earth is not in danger of tipping over, although this uneven growth is recorded in seismic wave speeds in the inner core of the planet.

Estimate the age of the nucleus

So does this approach help us understand the age of the inner core? When the researchers compared their seismic observations with their flow models, they found that the inner core — in the center of the entire core, which formed much earlier — is likely between 500 and 1.5 billion years old.

The study indicates that the younger end of this age group is more appropriate, although the older end agrees with it Appreciation It was made by measuring changes in the strength of the Earth’s magnetic field. Whichever number is correct, it is clear that the inner core is relatively young, between one-ninth and one-third the age of the planet.

This latest work presents a powerful new paradigm of the inner core. However, a number of material assumptions made by the authors must be true in order to be true. For example, the model works only if the inner core consists of a specific crystalline phase of iron, around which there is some uncertainty.

And does this uneven inner core make the Earth unusual? It turns out that many planetary bodies have two halves that differ somewhat from each other. employment MarsThe northern half is smaller, while the southern half is more mountainous. Shell color The proximal side is chemically different from the far side. employment Mercury And Jupiter It is not the surface that is uneven, but rather the magnetic field that does not form an inverse north-south picture.

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Thus, although the reasons for all these disparities are different, Earth appears to be in good shape as a somewhat asymmetric planet in a solar system of asymmetric celestial bodies. (I)


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