Fri. Aug 12th, 2022

Earth’s ‘solid’ inner core may not be so solid after all! Spherical mass 3200 miles below the surface contains both mushy and hard iron, study claims

  • The inner core of the earth is not solid, but actually contains the mushy and hard iron – study
  • Researchers claim that the core consists of a series of fluid, soft and hard structures
  • Because the inner core is so inaccessible, they used earthquake waves for study
  • How seismic waves travel can identify minerals, heat, and density of the Earth’s layers


No human or machine has ever been 3,200 miles below the Earth’s surface because depth, pressure and temperature make it inaccessible.

But scientists have long believed that the inner core of our planet was solid, in contrast to the liquid metal region that surrounds it.

Now, a new study has been questioned claiming that the spherical mass responsible for the Earth’s magnetic field contains both porridge and hard iron.

Scientists have long believed that the inner core of our planet was solid.  Now it has been questioned by a new study claiming that the spherical mass contains both mushy and hard iron.  Earthquake waves (pictured) were used as the basis for the research

Scientists have long believed that the inner core of our planet was solid. Now it has been questioned by a new study claiming that the spherical mass contains both mushy and hard iron. Earthquake waves (pictured) were used as the basis for the research

Four layers on planet Earth

Crust: To a depth of up to 70 km, this is the outermost layer of the earth, covering both sea and land areas.

Kappe: Goes down to 2,890 km with the lower mantle, this is the planet’s thickest layer and made of silicate rock that is richer in iron and magnesium than the crust overhead.

Outer core: Running from a depth of 2,890-5,150 km, this region is made of liquid iron and nickel with trace lighter elements.

Inner core: Going down to a depth of 6,370 km in the center of planet Earth, this region has been thought to be made of solid iron and nickel. But this new study suggests that it contains both porridge and hard iron.

The research has been led by Rhett Butler, a geophysicist at the University of Hawaii, who suggests that the Earth’s ‘solid’ inner core actually consists of a series of fluid, soft and hard structures that vary across the top 150 miles of mass.

The earth’s interior is layered like an onion. The iron-nickel inner core is 745 miles in radius, or about three-quarters of the size of the moon, and is surrounded by a liquid outer core of molten iron and nickel that is about 1,500 miles thick.

The outer core is surrounded by a mantle of hot rock 1,800 miles thick and superimposed by a thin, cool, rocky crust at the surface.

Because the inner core is so inaccessible, scientists had to rely on the only means available to study the innermost earth – earthquake waves.

‘Illuminated by earthquakes in the crust and upper mantle, and observed by seismic observatories on the Earth’s surface, seismology provides the only direct way to study the inner core and its processes,’ Butler said.

As seismic waves move through different layers of the Earth, their velocity changes and they can reflect or break depending on the minerals, temperature and density of this layer.

To better understand the functions of the Earth’s inner core, Butler and his co-author Seiji Tsuboi, a researcher at the Japan Agency for Marine-Earth Science and Technology, used data from seismometers directly opposite the site of an earthquake.

They used Japan’s Earth Simulator supercomputer to assess five matings to largely cover the inner core area: Tonga and Algeria, Indonesia and Brazil, and three between Chile and China.

An intersection of the Earth's interior shows the inner core (red) and the liquid iron outer core (orange).  Seismic waves move faster through the Earth's inner core between the North and South Poles (blue arrows) than over the equator (green arrow)

An intersection of the Earth’s interior shows the inner core (red) and the liquid iron outer core (orange). Seismic waves move faster through the Earth’s inner core between the North and South Poles (blue arrows) than over the equator (green arrow)

Because Earth's inner core is so inaccessible, scientists had to rely on the only means available to study the innermost earth - earthquake waves (stock image)

Because Earth’s inner core is so inaccessible, scientists had to rely on the only means available to study the innermost earth – earthquake waves (stock image)

‘In stark contrast to the homogeneous, soft iron alloys considered in all soil models in the inner core since the 1970s, our models suggest that there are adjacent areas of hard, soft and liquid or mushy iron alloys in the upper 150 miles of the inner core, ‘said Butler.

‘This puts new constraints on the Earth’s composition, thermal history and evolution.’

The scientists said that this discovery of the diverse structure of the inner core could offer important new information about the dynamics at the boundary between the inner and outer core that affect the Earth’s magnetic field.

‘Knowledge of this boundary state from seismology can enable better, predictable models of the geomagnetic field that protect and safeguard life on our planet,’ Butler said.

Scientists now plan to model the inner core structure in more detail using the Earth Simulator supercomputer so they can see how it compares to different properties of the Earth’s geomagnetic field.

The research has been published in the journal Science Direct.

EARTH’S LIQUID IRON CORE CREATES THE MAGNETIC FIELD

Our planet’s magnetic field is thought to be generated deep inside the Earth’s core.

No one has ever traveled to the center of the earth, but by studying shock waves from earthquakes, physicists have been able to calculate its probable structure.

At the heart of the Earth is what was thought to be its solid inner core, two-thirds the size of the moon, made mostly of iron. However, this new study disputes this.

At 5,700 ° C, this iron is as hot as the surface of the sun, but the crush pressure caused by gravity prevents it from becoming liquid.

Around this is the outer core, which is a 1,242-kilometer-thick layer of iron, nickel, and small amounts of other metals.

The metal here is liquid due to the lower pressure than the inner core.

Differences in temperature, pressure and composition in the outer core cause convection currents in the molten metal as cool, dense substances sink and hot matter rises.

The ‘Coriolis’ force, caused by the Earth’s spin, also causes swirling vortices.

This current of liquid iron generates electric currents, which in turn create magnetic fields.

Charged metals passing through these fields create their own electric currents, and then the cycle continues.

This self-supporting loop is known as the geodynamo.

The spiral caused by the Coriolis force means that the separate magnetic fields are largely aligned in the same direction, and their combined effect adds up to producing a large magnetic field that engulfs the planet.

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