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Earth's inner core is the innermost geologic layer of the planet Earth. It is primarily a solid ball with a radius of about 1,220 km (760 mi), which is about 20% of Earth's radius or 70% of the Moon's radius. [1] [2] There are no samples of the core accessible for direct measurement, as there are for Earth's mantle. [3]
The existence of an inner core was proposed by Adam Dziewonski and Miaki Ishii to explain the discrepancies in certain fits to travel-time wave models of the inner core. [1] It is contested whether the innermost inner core is a distinct entity, and it is claimed that the data can be explained in other ways.
Earth's inner core is the innermost geologic layer of the planet Earth. It is primarily a solid ball with a radius of about 1,220 km (760 mi), which is about 19% of Earth's radius [0.7% of volume] or 70% of the Moon's radius. [32] [33] The inner core was discovered in 1936 by Inge Lehmann and is composed primarily of iron and some nickel. Since ...
The inner core is anisotropic, causing seismic waves to vary in speed depending on their direction of travel. P-waves, in particular, move more quickly along the inner core's rotational axis than across the equatorial plane. [42] This suggests that Earth's rotation affects the alignment of iron crystals during the core's solidification. [46]
The core contains half the Earth's vanadium and chromium, and may contain considerable niobium and tantalum. [26] The core is depleted in germanium and gallium. [26] Core mantle differentiation occurred within the first 30 million years of Earth's history. [26] Inner core crystallization timing is still largely unresolved. [26]
For the inner core to rotate despite gravitational coupling, it must be able to change shape, which places constraints on its viscosity. A 2023 study reported that the spin of the Earth's inner core has stopped spinning faster than the planet's surface around 2009 and likely is now rotating slower than it. [1]
Earth's inner structure can be described both chemically (crust, mantle, and core) and mechanically. The lithosphere–asthenosphere boundary lies between Earth's cooler, rigid lithosphere and the warmer, ductile asthenosphere .
In the Pressure and Gravity section, change The acceleration of gravity at the surface of the inner core can be computed to be 4.3 m/s2;[22] which is less than half the value at the surface of the Earth (9.8 m/s2). to The acceleration of gravity at the surface of the inner core can be computed to be 0.43 m/s2;[22] which is less than 1/20 the ...