Simone Lawson
The Earth's innermost layer is a subject of intrigue for scientists, who have long sought to understand the composition of the Earth's core. Recent studies have revealed that the Earth's core may have a distinct innermost layer, estimated to be a 400-mile-wide (644-kilometer-wide) ball of iron and nickel alloy. This discovery was made possible by analysing seismic waves from earthquakes, which pass through the Earth's core and provide valuable insights into its structure. The innermost layer is believed to be solid due to the extreme pressure, despite the incredibly high temperatures. This hidden layer within the Earth's core could offer new clues about the evolution of our planet and its magnetic field.
| Characteristics | Values |
|---|---|
| Composition | Iron-nickel alloy with trace amounts of other elements |
| Radius | 1,220-1,230 km (758-760 miles) |
| Width | 2,500 km |
| Temperature | 5,430 °C (9,800 °F) or 5,000-6,000 °C |
| State | Solid |
| Distinctive features | "Innermost inner core" (IMIC) or "inner inner core" (IIC) with different properties to the outer shell |
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What You'll Learn
The inner core is a huge ball of metal, 400 miles wide
The Earth is composed of four distinct layers, starting from the innermost: the inner core, the outer core, the mantle, and the crust. The inner core is a solid ball with a radius of about 1,220-1,230 km (758-760 miles), constituting about 20% of Earth's radius or 70% of the Moon's radius. It is located about 6,400-5,180 km (4,000-3,220 miles) beneath the Earth's surface.
The inner core is believed to be composed of an iron-nickel alloy with trace amounts of other elements. The temperature at its surface is estimated to be approximately 5,430 °C (9,800 °F), which is comparable to the temperature at the surface of the Sun. The metal at the inner core remains solid despite the high temperature due to the extremely high pressure, in accordance with the Simon-Glatzel equation.
In 2023, a study reported evidence of an "anisotropically-distinctive innermost inner core", a 650-km thick inner ball with a transition to a weakly anisotropic outer shell. This innermost inner core was found to have a distinct anisotropy, a property that allows it to exhibit different characteristics depending on the angle of approach. This discovery was made by studying the speed of seismic waves passing through the core, which varied depending on the direction of travel.
The inner core is believed to be a huge ball of metal, approximately 400 miles wide, constituting the innermost layer of the Earth. This finding has significant implications for understanding the Earth's magnetic field and provides a glimpse into the formation and evolution of not only our planet but also other planets in our solar system.
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It is composed of an iron-nickel alloy, with some other elements
The Earth's innermost layer, the inner core, is a ball of iron with a radius of about 1,220-1,230 km (758-760 miles), or about three-quarters that of the moon. It is located 6,400 to 5,180 km (4,000 to 3,220 miles) beneath the Earth's surface. The inner core is believed to be composed primarily of an iron-nickel alloy, with some other elements present in trace amounts. This composition was deduced from measurements of seismic waves and the Earth's magnetic field.
The inner core is distinct from the molten outer core, which is also composed of iron and nickel. The inner core is solid despite the extremely high temperatures due to the high pressure acting on it, in accordance with the Simon-Glatzel equation. The temperature at the surface of the inner core is estimated to be approximately 5,430 °C (9,800 °F), which is comparable to the temperature at the surface of the Sun.
In recent years, new evidence has emerged suggesting that the inner core may have an additional hidden layer, an "innermost inner core" (IMIC) or "inner inner core" (IIC), with a radius of 300-750 km or about 500 km, respectively. This layer is believed to have different properties than the outer shell surrounding it, causing seismic waves to pass through it at different speeds. The presence of this distinct innermost core could provide valuable insights into the Earth's magnetic field and its evolution.
The inner core is the hottest layer of the Earth, and its rotation may have paused or even reversed, according to some scientists. The Earth's core, including the inner core, plays a crucial role in generating the planet's magnetic field through the movement of its metals.
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The inner core is solid due to high pressure and temperature
The Earth is composed of four distinct layers: the inner core, the outer core, the mantle, and the crust. The inner core is the innermost layer and the hottest, with temperatures similar to the surface of the sun—approximately 5,430 °C (9,800 °F). Despite these extreme temperatures, the inner core remains solid due to the extremely high pressure exerted by the layers above it.
The phase of a substance (solid, liquid, or gas) is determined by factors such as temperature, pressure, and composition. At high temperatures, molecules vibrate more and push against each other, breaking the bonds that hold them together and allowing the substance to flow, becoming a liquid. However, in the Earth's inner core, the immense pressure exerted by the surrounding layers prevents this from happening.
The inner core is composed primarily of iron, with some nickel and other elements. Iron has a high melting point, and the extreme pressure raises this melting point even higher. This high pressure, combined with the high melting point of iron, results in a solid inner core despite the extremely high temperatures.
The pressure decreases as we move away from the inner core, and at a certain point, the temperature becomes high enough to melt the iron, resulting in the liquid outer core. This phenomenon illustrates how pressure and temperature work together to determine the phase of a substance.
The solid inner core is believed to have a radius of about 1,230 km (760 miles), which is about 20% of Earth's radius or 70% of the Moon's radius. While there are no direct samples of the inner core, scientists have deduced its characteristics through measurements of seismic waves and the Earth's magnetic field. These studies have also suggested the presence of an ""innermost inner core" (IMIC) within the solid inner core, indicating a complex structure to our planet's centre.
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Seismic waves reveal the inner core's distinct anisotropy
The Earth is composed of four distinct layers, namely the inner core, the outer core, the mantle, and the crust. Except for the crust, no human has ever explored these layers in person. The deepest humans have drilled is just over 12 kilometers (7.6 miles), which took 20 years. Scientists have studied the inner workings of the Earth by analysing earthquake waves and their speed and behaviour as they encounter layers of different densities.
In 2023, a study reported new evidence for an "anisotropically-distinctive innermost inner core". This innermost layer is a solid metallic ball with a thickness of about 650 km, sitting within the centre of the inner core. The findings, published in Nature Communications, confirm the existence of a fifth layer inside the Earth.
Seismic waves are used to study the inner core as they can reveal the physical properties of the inner core as they pass through it. By measuring the different speeds at which these waves penetrate and pass through the Earth's inner core, researchers were able to document evidence of a distinct layer inside the Earth. The variation in travel times of seismic waves for different earthquakes suggests that the crystallised structure within the inner core's innermost region is different from the outer layer.
The inner core is composed of an iron-nickel alloy with some other elements. The anisotropy of this alloy is described by how seismic waves speed up or slow down as they pass through the material, depending on the direction in which they travel. This could be caused by the different arrangements of iron atoms at high temperatures and pressures or the preferred alignment of growing crystals.
The study of seismic waves provides a new way to probe the Earth's inner core and its evolutionary history. By analysing seismic waves, researchers can gain insights into the structure and composition of the Earth's inner layers, as well as a better understanding of the formation of the inner core.
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The inner core spins faster than the rest of the planet
The Earth is composed of four distinct layers: the inner core, the outer core, the mantle, and the crust. The inner core is the innermost layer of the Earth and is a solid ball with a radius of about 1,220-1,230 km (758-760 miles), constituting about 20% of Earth's radius or 70% of the Moon's radius. It is composed of an iron-nickel alloy with some other elements and has a temperature of around 5,430 °C (9,800 °F) at its surface. The inner core is believed to be solid due to high pressure, despite the extremely high temperatures.
The inner core is not only remarkable for being the Earth's innermost layer but also for its rotational behaviour. It was discovered in 1996 by two seismologists that the inner core rotates independently from the rest of the planet and completes a full revolution in about 400 years. This means that the inner core spins faster than the rest of the planet, gaining a quarter-turn on the whole planet over the past 100 years. This discovery has significant implications for understanding the Earth's magnetic field and the flow of heat through the planet.
The rotational behaviour of the inner core is known as super-rotation, which refers to the inner core's faster net rotation rate relative to the Earth as a whole. This phenomenon was first predicted in 1981 by David Gubbins, who suggested that a differential rotation between the inner and outer cores could generate a large toroidal magnetic field, causing the inner core to drift westward. Subsequent studies in 1995 and 1996 provided seismic evidence supporting the super-rotation hypothesis, with estimated rates of 0.4 to 3 degrees per year.
The inner core's super-rotation is driven by the magnetic and electrical effects within the nearly frictionless liquid outer core. Seismic wave readings have been instrumental in tracking the inner core's rotation and have revealed that waves travelled faster in the 1990s than in the 1960s, indicating the inner core's faster movement. Additionally, observations have shown that waves travel faster between the north and south poles than along the equatorial plane, with a more complex model of anisotropy being developed over time.
The inner core's super-rotation has sparked further research into understanding the Earth's magnetic field and its periodic reversals, as well as the flow of heat through the planet. While the super-rotation hypothesis has been disputed by some later seismic studies, it has provided valuable insights into the Earth's inner workings and continues to be an area of active investigation.
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Frequently asked questions
The innermost layer of the earth is a 400-mile-wide ball of iron. This layer is also known as the inner core and is located about 1,600 kilometers beneath the earth's surface.
The temperature of the inner core is estimated to be approximately 5,430 °C (9,800 °F), which is similar to the temperature at the surface of the Sun.
The inner core is believed to be composed of an iron–nickel alloy with some other elements.
