More than 5,000 kilometers below us, the huge metal core of the earth was not discovered until 1936. Almost a century later, we are still trying to answer basic questions about when and how it formed. We cannot directly sample the inner core, so the key to unlocking the inner core lies in the cooperation between seismologists. Seismologists use seismic waves and geodynamic waves to indirectly sample its dynamics, and mineral physicists study its behavior by analyzing Ferroalloys under high temperature and pressure.
In a new study, they show how the inner core of the earth grows faster on one side than on the other. Combining this knowledge scientists are trying to answer what’s happening miles under our feet, and the fascinating history of the Earth’s magnetic field.
The core of the earth formed very early, in the 4.5 billion years of our planet’s history, that is, the first 200 million years. Gravity pushes the heavier iron toward the center of the young planet, causing the hard silicate minerals to form the mantle and crust.
The formation of the earth trapped a lot of heat inside the earth. Due to continuous radioactive decay, this loss of heat and warming stimulated the development of our planet. The heat loss inside the earth causes the high-energy flow of liquid iron in the outer core of the earth to move, thereby generating the earth’s magnetic field. At the same time, the cooling of the insides deep in the earth contributes to the development of the tectonic plates that make up the surface of our planet.
In the 1990s, scientists discovered that the velocity of seismic waves passing through the inner core suddenly changed, which indicated that something asymmetrical was happening inside the inner core. Especially the eastern and western half of the inner core showed different seismic velocity changes. The inner core lies under Asia, the Indian Ocean, and the Western Pacific to the east, and the west is under the Atlantic Ocean in the Americas, and the East Pacific.
You can think of this uneven growth as if you are trying to make ice in a refrigerator that can only work on one side, and ice cubes only form on one side of the refrigerator where cooling is effective. Similarly, core growth on one side is more because the rest of the earth absorbs heat from some parts of the inner core faster than others.
But unlike ice cubes, the hard core bears gravity and distributes the growth evenly through the progressive internal flow that maintains the spherical shape of the core. This means that the earth is not in danger of overturning, even though the seismic wave velocity in the inner core of the earth records this uneven growth.