Why is the inner core solid and not liquid

• Earth is filled with many mysteries that we are yet to unravel and in 1936, its discovered that the structure of Earth’s deep core has remained a mystery.
• Physicists thought it was solid at first, but a new study reveals it’s a mix of solid and liquid.
• Such research has the potential to reveal some, but not all, of our planet’s darkest secrets, and Earth, has also been the topic of many scientific inquiries, but due to its extremely high temperatures and pressure, it is inaccessible to researchers to sample and examine.

Compared to many other solar systems, Earth has many mysterious discoveries that are yet to be revealed. Earth contains so many attributes and functions that are the subject of many queries from the scientist. It is an official statement that Earth’s inner core is solid.

S-waves could not travel through this region, but pressure waves did and could be detected at the surface, the liquid nature of the inner core was established early in the development of global seismology.

S-waves are shear waves, and most liquids do not support shear pressures. The solid inner core was determined from phase relationships and the core’s temperatures and pressures, which reveal the core steadily crystallizing from the center out.

Earth’s inner and outer core is formed of an iron and nickel alloy. Although the inner core is exceptionally heated, it is solid due to the extremely high pressure. To solidify the heat, the pressure is insufficient for the outer core. Temperature and pressure rise as one descends further into the Earth.

Why is the inner core solid?

The Earth’s inner core is solid, but the outer core is liquid if both regions have a very high temperature. The inner core is solid because it is composed of dense or heavy elements such as iron and nickel.

The outer core is solid because the average magnetic field strength in the Earth’s outer core was calculated to be 2.5 million Tesla, which is 50 times higher than the magnetic field at the surface. The outer core is not as pressurized for solid. Therefore, it is liquid while having the same composition as the inner core.

Even when extremely high temperatures, some materials do not melt and thus remain solid. It turns out that many materials can solidify at greater temperatures if the pressure is likewise elevated.

What makes the Inner core and Outer core different?

The inner and outer cores are chemically similar both are mainly iron with a bit of nickel and other chemical elements; the only difference is that the outer core is liquid while the inner core is solid.

As a result, scientists have calculated the density of different regions of the Earth’s core, mantle, and crust by observing different seismic waves from several earthquakes around the world. It’s based on the waves which are passed through the cores easily.

The pressures and temperatures in the inner core are so high that the metals are packed together and unable to move like a liquid, forcing them to vibrate instead of solidifying.

What does the outer core perform or do?

The outer core is the third layer of the Earth. The outer core is in charge of the Earth’s magnetic field. The iron inside Earth’s liquid outer core flows about as it rotates on its axis. Powerful electric currents form in the liquid iron due to the movement.

What’s common in the inner core and outer core?

The Earth’s core comprises a solid inner core and a liquid outer core that is primarily comprised of iron. Outside of these areas is the mantle, followed by the crust, on which humans live. Earth scientists believe that the Earth’s core controls the planet’s magnetic field and plate tectonics

We've known for a while that Earth's deepest depths, its "solid iron" inner core, isn't made of pure iron — and now scientists say it might not be solid either.

Simulations by a team of researchers in China suggest our planet's innards are somewhere between solid and liquid in a "superionic" state.

The researchhas been published in the journal Nature.

Yu He, a physicist at the Chinese Academy of Sciences and co-author of the study, said the calculations were "a new starting point to understand the inner core".

This study, and others like it, Dr He added, might one day help earth scientists solve some fundamental but complex problems, such as when the inner core started to take shape.

But the new study can't completely explain all the inner core's quirks.

Why states of matter matter

On the surface of the Earth, we generally deal with three states of matter: solid, liquid and gas.

Take water, for instance. As ice in a cool drink, water molecules are arranged in a regular, 3D crystal. When that ice melts to become liquid water, those molecules can now move around, but are still in close proximity.

And as a gas, like the water vapour that gives humid days their oppressive stickiness, those mobile water molecules are free to move far away from each other.

But when substances are subjected to intense pressure or heat, they can switch into other, weirder states of matter.

Such as superionic matter, which is somewhere between liquid and solid.

In superionic water, molecules split apart into oxygen and hydrogen atoms.

The oxygen atoms crystallise into a 3D structure — like you'd see in a solid — while hydrogen atoms move freely around, like a liquid.

Superionic water ice could make up the bulk of giant icy planets, such as Neptune and Uranus.

And some geophysicists think the very centre of Earth, its inner core, is superionic too.

Instead of water, though, the inner core is made of a metal alloy: mostly iron, a bit of nickel, and a few other much lighter elements, such as hydrogen and carbon, mixed in there too.

It's the iron atoms that form the 3D "solid" structure in a superionic state, and the lighter elements that flow around it like liquid.

Earthquakes used to probe Earth's core

Earth's inner core reaches temperatures similar to the surface of the Sun, and pressures 3.7 million times what we experience at sea level.

Physically digging to the inner core is impossible, and we can't yet recreate its conditions in the lab.

So to get an idea of what the inner core is like, scientists measure how seismic waves, generated by earthquakes, change in speed and direction as they rumble through the centre of the planet.

This information can tell scientists how dense the inner core's iron alloy is, as well as its stiffness, said Hrvoje Tkalcic, a geophysicist at the Australian National University who was not involved in the work.

"And then we also have mineral physics, geodynamics and mathematical geophysics trying to work together to figure out what the heck is happening at the centre of our planet," Professor Tkalcic said.

Dr He and his crew used computer simulations to see how seismic waves might travel through an alloy made of iron, hydrogen, carbon and oxygen under immense pressure and heat.

They're not the first to do this: other studies have done similar, albeit with fewer lighter elements included.

The new study's conclusions are in line with what scientists have deduced from earthquakes: that the core is less dense than pure iron, so lighter elements must be mixed in, and it's relatively soft.

"And that's good. That's a step forward," Professor Tkalcic said.

But there's still a mystery

Something the new study can't fully explain is apeculiar but distinct feature of the inner core.

The speed at which a seismic wave moves through the inner core depends on its direction through the planet.

For instance, a wave travelling between north and south magnetic poles will ripple faster through the inner core than a wave travelling across the globe from equator to equator — even if they're travelling the same distance.

It's a phenomenon called seismic anisotropy, and why it happens, no-one's really sure.

Dr He and colleaguessuggest lighter, liquid-like elements are not evenly distributed through the superionic inner core.

Instead, they're concentrated into a flattened sphere around the middle, which puts the brakes onwaves passing through.

But how exactly how — and why — lighter elements might accumulate that way is not specified.

In any case, the middle of the planet definitely requires more scrutiny, Dr He said.

"I think more studies are needed to explain other seismic features, such as seismic anisotropy, in the inner core."

Posted 9 Feb 2022Wed 9 Feb 2022 at 6:30pm, updated 10 Feb 2022Thu 10 Feb 2022 at 2:34pm