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The Earth's structure - from the inner core, to the magnetosphere

First of all, let's clear up that nobody has ever taken direct samples of the Earth's core, whether that be from the inner or outer sections as we will later discuss. Therefore, most of the information that's currently out there about the Earth's structure is mostly theoretical.

If you're unfamiliar with how scientists currently believe the Earth is structured, then don't worry!

We'll be talking all about that here, but I just wanted to introduce this post with an important disclaimer that all of this is essentially theory since nobody has ever taken samples of the Earth beneath the crust.

With that out of the way with then, let's start with the structure that makes up the body of our planet, before taking a closer look at the atmosphere and beyond!


Our planet is composed of four distinctive layers.

Starting from the innermost layer, we have the inner core as you might have already guessed.

This highly pressurised region of solidified nickel and iron stretches around 1,520 miles in diameter.

Here, temperatures are well in excess of 5000 degrees celsius, which is similar to the surface of the Sun!

Don't worry if you're confused why the core is still solid if temperatures exceed 5000 degrees Celsius...We'll be talking about that in a minute!

Enveloping the inner core is what's known as the outer core, where pressure adequately drops to allow for iron and nickel to take fluid-like states, and this layer is thought to extend around 1400 miles.

The idea of iron and nickel being molten here is an important one as we come to talk about the Earth's magnetic field!

In between the outer core and the crust is the thickest layer of all 4 - the mantle, which is about 1800 miles in thickness.

This layer is a hot, viscous mixture of molten metals that interact with the crust via convection currents that cause the Earth's crust to move, albeit very slightly, and the aftermath of such movements can take appearance as mountains, ravines, valleys and volcanoes.

Finally, we have the crust.

This layer is by far the least thick, measuring only 19 miles deep before reaching the mantle on average.

I say "on average", because it changes depending on where in the world we're talking about!

This is the layer that both you and I are currently standing/sitting upon and it's mostly comprised of many different rocks of salt, metals and water that clump together to form the soil that we're all familiar with.

So those are the main layers that make up Earth's body.

Remember that our planet, just like ever other planet in our solar system, has been evolving over billions of years.

The Earth would've likely formed from the collisions of millions of rock particles that glued together under the extreme temperatures generated from such collisions.

In the planet's early formation, it would've been totally unrecognisable from today, resembling more a of a desolate, fire-stricken lava pool.

The Earth's been gradually cooling ever since, although the extreme pressures found at the core and mantle drive temperatures of over 5000 degrees celsius, as previously mentioned.

Moving onto the atmosphere though, we can yet again divide this up into separate layers.

Starting from the closest to the surface, we have:

The troposphere, the stratosphere , the mesosphere , the thermosphere, the exosphere

Some of them you might be familiar than others, particularly the stratosphere as it gains a lot of attention in the media due to climate change.

This is also where commercial airliners fly, but we'll talk more about that in minute!

The troposphere

The troposphere begins at the Earth's surface and extends 4-12 miles high, depending on where in the world you are, since it's higher at the equator where higher temperatures can drive higher convection currents and allow the gas particles to rise further (maybe you've heard that "heat rises"...)

This is the most familiar layer to you and I - it contains the air that we breathe, the water vapour, the rain, the clouds and our overall weather system is contained within this layer.

The stratosphere

Beyond it, however, is probably the most "famous" layer - the stratosphere. This layer begins where the troposphere ends, and it continues on for another 31 miles or so before reaching the mesosphere.

I say it's the famous layer, simply because it's often mentioned with all things climate-change related, as the stratosphere holds a layer of oxygen that we call the O-zone layer, which you've probably heard of in the news before.

As the name might already suggest, it's an oxygen layer, although here molecules of oxygen don't represent themselves in the same way as they do at the surface...

Oxygen is what we call a diatomic element, along with several others such as chlorine and fluorine which means that it naturally exists as 2 oxygen atoms bonded together, as oppose to roaming around as the 1, as is the case with most elements.

Why does it do this?

Well, briefly, elements like oxygen and chlorine exist in the 6th column of the periodic table, meaning that they have 6 electrons in their outer shell which can take up to 8.

Because atoms naturally want to be "complete" in that they want their outer shell to be completely full of electrons, oxygen atoms bond to each other so that they both share 2 electrons each, forming a covalent bond (as you may or may not remember from school), such that they both have complete outer shells - that's the gist of it anyway.

So how is the oxygen at the surface different to the oxygen in the O-zone layer?

While oxygen comes as O₂ at the surface (2 oxygen atoms covalently bonded together), it prefers to take the form of O₃ in the O-zone layer, which has some interesting consequences for the way that it interacts with not only matter, but more importantly sunlight!

The ozone layer protects us from harmful UV (Ultraviolet) radiation, and if you've read my other articles, then you'll know that UV radiation is more energetic than the visible light that we can see.

In summary, the ozone layer protects us from a lot of this harmful UV radiation.

Something that's not all that important but worth mentioning for the curious folk, is that the stratosphere is also where commercial airplanes fly (about 30km up).

The mesosphere

Up next we have the mesosphere, which extends a further 22 miles or so on from the end of the stratosphere, marking its highest point at around 50 miles up from the surface.

This layer is also extremely important, perhaps even more so than the stratosphere, although it's not due to any characteristic that's unique to the mesosphere...

It's important simply because it shields the surface, and hence us, from potentially harmful meteoroids

Before I continue, you should know that meteoroids refer to debris that makes into the Earth's atmosphere, but burns up to form a meteor, where as if the meteoroids make it through the atmosphere and collide with the surface, they're referred to as meteorites.

Just one that's worth remembering!

Meteoroids regularly enter the Earth's atmosphere, but they're acceleration due to gravity gives them velocities of up to 41 miles per second!

Obviously that's incredibly high, and at that speed, the friction with the air particles that make up the atmosphere can generate temperatures of up to 1800 degrees Celsius.

At that temperature, along with the force felt from colliding with air particles at 41 miles per second, more often than not the meteoroids burn and break up into smaller particulates that shortly after disintegrate into mere dust.

At 1800 degrees, they shine incredibly brightly, although the light from the Sun almost always overrides that light during the day.

At night however, they can easily be seen as I'm sure many of you already know!

Just to put the force that you would feel travelling at this speed into perspective, try thinking about this:

If you've ever unwound your window on a motorway (or highway) and stuck your hand out of the window, you'll know that you can feel a fairly substantial force pushing against your hand.

Well, this is a force that's felt when travelling at 60 miles per hour or so, so you can only imagine the force felt at 40 miles per second!

Moving on to the thermosphere...

The thermosphere

The thermosphere is substantially larger than any of the previously named layers of the atmosphere, although it's not nearly as large as the exosphere, which we'll come on to shortly.

Coming in at over 319 miles in thickness, the thermosphere is home to low-orbit satellites such as the ISS (International Space Station).

At this distance, the acceleration due to the Earth's gravity is much lower than at the surface, which means the atmosphere is extremely thin.

In fact, I imagine you seemed pretty confused upon reading that the ISS orbits within Earth's atmosphere, as we usually think of the atmosphere as being a dense collection of gas particles!

In reality though, the thermosphere contains very little atmospheric particles relative to layers such as the troposphere, which means that temperatures can get extremely cold and sound waves no longer have a substantial enough medium of which to travel through.

The exosphere

Finally, we have the exosphere.

The largest of them all by a huge margin, the exosphere stretches around 6000 miles up from the thermosphere.

At this point, mere atoms and particles remain gravitational bound to Earth, but are so diluted that they don't have much interaction with each other in terms of collisions.

This is also where most of Earth's man-made satellites orbit.

Technically, we have another layer that I didn't mention earlier - the Magnetosphere.

Due to the convection of molten Iron at the outer core and mantle, as described earlier, Earth, like many other planets (but not all of them), generates a strong magnetic field.

This magnetic field plays a vital role in protecting us from both solar wind and solar flares that are ejected from the surface of the sun, which are themselves responsible for the northern and southern lights on Earth!

You can read more about that here, if you're interested.

Interestingly, it's not as easy to put a number on the overall size of the magnetosphere, as it's drastically different depending on which side of the Earth that we are talking about.

Specifically, the magnetosphere on the side that is facing the sun is drastically shorter than on the other side, as the bombardment of ions and other charged particles from the sun causes the magnetosphere to compress, as illustrated below.

Image Credit: NASA's Scientific Visualization Studio

Earth's magnetic field

And that's it!

Hopefully you learned something!

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