The Earth’s core has two parts, the inner and outer, with the outer being mostly liquid iron and nickel. The inner core was thought to be a single crystal of iron, but recent theories suggest it is made up of dissimilar parts. The outer core is responsible for the Earth’s magnetic field and circulates due to the Coriolis effect. The inner core is solid and younger than the Earth itself, and it rotates independently of the Earth’s surface.
The Earth has a core made up of two parts: the inner and the outer. The outer core is mostly liquid iron and some nickel, while the inside is mostly solid iron. For a while it was thought that the inner portion was a single crystal of iron, although more recent theories predict that it is more likely made up of dissimilar parts, with irregular characteristics. What scientists know about the core has been derived from seismic wave analysis and modeling based on accepted physics and chemistry.
The outer core begins at a depth of between 1,790 and 3,160 miles (2,890 to 5,150 kilometers), and there is a degree of uncertainty as to the precise depth. The inland section begins at a depth of 3,160 to 3,954 miles (5,150 to 6,360 kilometers). Above the outer section is the mantle, the largest portion of the Earth’s subterranean regions. Compared to deeper layers, the mantle is highly viscous and circulates continuously.
It is the outer section that is responsible for the earth’s magnetic field. It circulates freely due to the agitation caused by the Earth’s rotation, with its dynamics dictated by the Coriolis effect. The effect is similar to the circulation seen in pieces of pasta boiling in a pot. This constant circulation gives rise to the earth’s magnetic field, in a process called dynamo theory. Although the inner core is too hot to maintain a permanent magnetic field, it likely helps stabilize the field generated by the outer portion.
The Earth has not always had a solid inner core. Although the pressure is extremely high, it was so hot at one point that the whole thing was liquid. It has slowly cooled over time and is thought to be between 2 and 4 billion years old, younger than the Earth itself, which is about 4.5 billion years old. The inner section was discovered in 1936 by Inge Lehmann.
Since the inner core is a solid suspended in a liquid, it can rotate independently of the Earth itself. Most geophysicists believe it rotates about a third of a degree more on the surface each year. So, for about every 1,000 rotations of the earth’s surface, the interior rotates 1,001 times.
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