Chapter 1: What is Earth's inner core and why is it significant?
Over 3,000 miles below the surface, right at the centre of the Earth, lies a solid spheroid. Primarily made of iron and nearly as big as the Moon, its temperature rivals that of the Sun. This is Earth's inner core. It spins independently at the very heart of our planet. And while we can't see it for ourselves, its immense heat triggers processes that impact us all.
Plate tectonics that manifest in some of the most awe-inspiring and deadly sights on the surface. Our planet's invisible magnetic field, which makes life possible. It's no wonder that Earth's core has captured the imaginations of generations of scientists who have developed ever more sophisticated instruments to investigate its fiery depths.
And the latest research efforts have yielded discoveries that could have come straight from a Hollywood film. Our inner core appears to not only have stopped spinning, but has in fact started moving backwards. Why has this happened? And what does it mean for us, topside? I'm James Stewart, and you're watching Astrum Earth.
Join me as we quite literally explore our planet's deepest, darkest secrets. We'll investigate its inner workings, assess the implications of our cause change in motion, and ask the question, how worried should we be?
In order to get to our planet's core, we need to go down. Call it my version of a journey to the centre of the Earth. Each layer has its own role in creating, sustaining and sometimes destroying the world above. And all of them are influenced by the solid iron heart. Here at the surface, we walk upon the crust, a mere brittle shell.
Though it feels pretty solid to us, it is in fact fractured into giant tectonic plates that drift, collide and grind past each other, causing violent earthquakes and devastating volcanic eruptions. How it moves is all thanks to the layer below, the mantle. This layer also appears solid, but is actually flowing very, very slowly, at the rate of a few centimetres a year.
This tiny but inexorable movement contributes to the plate tectonics that impact our surface world. Dig deeper still and you reach the outer core, a sea of iron and nickel with its own heat-driven currents. Its motion generates the Earth's magnetic field, which protects life on our planet from deadly solar particles. Finally, suspended in this outer core is that primarily iron inner core.
Here, the temperature reaches 6,000 degrees Celsius. Due to the immense pressures, the metal isn't liquid, but solid, forming a spheroid shape, like a slightly squashed sphere. This is our planet's boiler room. Its heat triggers the processes in the layers above.
driving those all-important convection currents in the outer core and ultimately contributing to the plate tectonics that shift the Earth's crust. It's easy to take for granted that we understand our planet's structure, but in reality that knowledge was incredibly hard won.
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Chapter 2: What recent discoveries have scientists made about the inner core?
It had already been established by this point that longitudinal waves can pass through both solids and liquids, but transverse waves can only pass through solids, and you can probably see where this is going.
Since the seismic waves had travelled through the inside of Earth to reach the seismograms, the resulting seismographs could yield information about what they passed through, namely, the structure of Earth itself. This realisation would allow centuries of speculation to finally be put to rest.
Put simply, Oldham noticed that waves that had travelled a long way to distant seismographs seemed to travel much slower than the six kilometres per second it usually moved through the mantle. To explain this, he concluded that they had traversed a central core composed of matter which transmits them at a slower speed, three kilometres per second to be exact.
He calculated the size of this core to be four tenths of the Earth's radius, deduced that it bends earthquake waves and that it behaves fundamentally differently to the rest of the Earth's interior. But he did not speculate as to what this core might be made of, refusing to go beyond what he could prove with data.
And so by the early 20th century, you had a theory that the Earth had an iron core and apparent proof that some sort of core did in fact exist. We were finally beginning to crack the inner structure of our planet. And yet, despite these great strides, these pioneers missed something.
Sometimes I get so focused on all the awesome stuff happening below our feet, I forget that the stuff on land also needs a bit of love too, perhaps now more than ever. That's where our friends at Planet Wild come in. They are a community-based nature protection organisation fighting back. Think of them like crowdfunding, but for nature.
Each month, their community funds a project to restore nature around the world and then documents it with a YouTube video report so you can see the impact of your contribution. It's actually their transparency that inspired us to become members in the first place.
And with so much plastic waste around, especially at this time of year after Christmas, one of my favourite projects they're working on right now is a breakthrough that could stop plastic from reaching the oceans. Now, my background is actually in sustainability, and I'm very, very personally invested in what these guys are doing.
So much so, I wanted to give as many of you the chance to get involved too. The first 100 people to sign up to Planet Wild using my code ASTRUM1 will get their first month paid for by me. Yes, just scan the QR code on screen right now or click the link in the video description.
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