Earth’s core is finally confirmed to be solid
Scientists have finally confirmed the theory that Earth has a solid core after uncertainty lingered over the topic for more than 80 years.
It has long been believed that Earth has a solid iron core but no proof has ever been found and it has been heralded as the ‘holy grail’ of global seismology.
The issue has finally been put to bed by re-purposing a technique that was first used to measure the thickness of the Antarctic ice sheet.
Researchers built a ‘fingerprint’ of our planet from the echoes of earthquakes and found that the innermost region of the planet is indeed solid, but not as hard as was scientists believed it to be.
Scientists have finally confirmed the theory that Earth has a solid core after uncertainty lingered over the topic for more than 80 years. They traced the origins of a specific seismic wave for proof of Earth’s solid core.
Associate Professor Hrvoje Tkalčić and PhD Scholar Than-Son Phạm from the Australia National University (ANU) studied shear waves, or ‘J waves’, in the Earth’s inner core.
J waves are produced by earthquakes and only travel through solid objects.
Inner shear waves can not be directly observed as they are of such little energy so the researchers looked for a creative way to detect them.
To do this they looked at the similarities between the signals received at different locations after major earthquakes.
A version of this method – known as the correlation wavefield method – has been used to calculate the thickness of the ice-shelf in Antarctica.
The same team then turned their method to the thorny issue of understanding Earth’s innermost secrets.
‘We’re throwing away the first three hours of the seismogram and what we’re looking at is between three and 10 hours after a large earthquake happens,’ Dr Tkalčic said.
‘We want to get rid of the big signals.’
These earthquake ‘echoes’ were compared to many others from different readings of the same earthquakes and this produced a ‘fingerprint of the Earth’.
The theory that Earth has a solid core was first proposed in 1936 when female Danish seismologist Inge Lehmann reanalysed data from the magnitude-7.3 1929 earthquake that struck New Zealand’s south island.
WHAT IS THE INSIDE OF EARTH LIKE?
Earth is made up of several different layers, each with unique properties. At the deepest level is the inner core which is believed to be solid. This produces Earth’s magnetic field and protects us from cosmic radiation.
The next layer is Earth’s liquid core which is a fluid layer about 2,200 km (1,400 miles) thick and composed of mostly iron and nickel. The mantle is the largest region of subterranean Earth and makes up around 84 percent of the planet’s volume.
It sits between the crust and the outer core and is broken down into two sections – upper and lower. The asthenosphere is a part of the upper mantle that sits below the lithosphere and is believed to be involved in plate tectonic movement.
The lithosphere is the region of the planet that is known as the crust and some pats of the uppermost mantle. it features everything we think of as the ground.
It is made up predominantly of silica and is broken up into the tectonic plates.
The Lithosphere-Asthenosphere boundary (LAB) is defined by a difference in response to stress.
The plates and the lithosphere often remain rigid but the weaker and more viscous asthenosphere can move and is know to move.
This movement causes plates to move into, underneath and below others and the LAB is the fundamental cause behind tsunamis and earthquakes as well as mountain range formation.
The green dots are receivers on the surface of Earth and the red dots are large earthquakes. The researchers from Australia National University (ANU) found this to be a fingerprint of the Earth
Researchers claim this study proves the existence of J waves – or sheer waves – in the inner core (pictured) an that this is proof the inner core is solid
Detectors in Europe picked up the waves and experts realised this would be impossible if the core was liquid, as it was thought to be in the 19th and early 20th centuries.
This theory became widely accepted and is taught to schoolchildren today but it had never been conclusively proved.
This researchers claim this ‘closes an 80-year quest to find them and confirms a solid, but soft, inner core’ the scientists claim’.
‘We found the inner core is indeed solid, but we also found that it’s softer than previously thought,’ Associate Professor Tkalčić explains.
‘It turns out – if our results are correct – the inner core shares some similar elastic properties with gold and platinum.
‘The inner core is like a time capsule, if we understand it we’ll understand how the planet was formed, and how it evolves.’
The research has been published in Science Magazine.
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jerry krause
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Hi Joe,
Hi,
I have long pondered what is the gas pressure at the center of a gaseous star or a ‘solid’ planet ? For it would seem the net influence of gravity upon the matter at the center should be zero. Therefore, it would seem the state of this matter at the center should depend upon its elemental composition, and based upon this composition, its temperature as it does at the surface of a solid planet where we generally ignore the influence of the atmospheric pressure upon the melting points of solids.
I write comments (essays) to see what I might claim to know and to not know. A fact, about which you will have to trust me, was I initially thought the matter (likely iron) at the earth’s center could not be a solid if it was surrounded by molten iron at a temperature greater than the melting temperature of iron. However, you wrote that the molten matter was not pure iron. Instead you described it as being an alloy of iron and nickel, which I have read others to have proposed. And it immediately became obvious that I did not know the melting point of this alloy.
So, what began as critical comment (correction) became a wrong idea.
So, why do I bother to submit this comment? I submit it because I consider (believe) wrong ideas hinder progress. And as I acknowledge this belief and still ponder I see there is another question which seems to need an answer: Why, or how is it, that the silver atoms of the molten phase of the alloy not diffuse into the solid, pure, iron atoms to convert the pure iron into an alloy with a slightly lesser silver atom composition.
For I must admit I am troubled by ‘scientists’ who seem to make mountains out of mole holes (subtle observations whose existence I question because they are so far removed from their claimed cause). For I am experimentalist and know the great care required to produce much simpler reproducible results in a laboratory setting. And I am aware of the history of ‘natural scientists’, or philosophers, who have refused to accept easily observed evidence that the earth moved or much obvious evidences of continental drift or today seem to ignore the obvious evidence of the influence of clouds upon the solar radiation that is transmitted through the natural atmosphere which maybe is cloud free only 50% of the daytime.
So, I write this comment to encourage readers and scientists to limit their pondering to easily, commonly, observed evidences which do need a simple explanation. .
Have a good day, Jerry
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Ken Hughes
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Actually, the results of these data show only that the SURFACE of the inner core is solid, NOT that it is solid all the way to the very centre. iron is molten at atmospheric pressure but as the pressure at the inner core surface is much greater, great enough to squash the very hot molten iron into the solid state, then clearly, the data shows this is what has happened. However, Jerry initially points out that the “pressure” at the very centre is zero, since gravitational effect act outwards in all directions. In this case, the (presumably) still very hot core exists in a region with no net pressure and so I might deduce that the very centre is in fact, liquid, surrounded by a solid shell. Our solid iron core has a “soft” centre? I would be interested to know what others think
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Herb Rose
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Hi Joe,
The Earth’s inner and outer cores both have a greater temperature than the Curie temperature of iron and nickel so there would be no ferromagnetism. Is the believed composition of these regions a result of the Earth’s magnetic field and how are these materials generating the magnetic field?
Have a good day,
Herb
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