Earth’s structure. Earth is actually ellipsoid, which means it’s shaped more like an ellipsis and not perfectly spherical. So a lot of times with the map, it looks like a sphere and you think of it as a perfect sphere, but it’s actually a little bit more elliptical.
So that means that the diameter is different through the poles than it is through the equator; because it is going to be a little bit longer one way than it is the other way.
Next Lesson: Earth’s Atmosphere
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Now that’s not a huge difference in the grand scheme of the Earth; because it does still look pretty spherical. But it is a little bit ellipsoid. So it’s important to remember that you’re not going to have a perfect center that is going to have the same distance on all sides; because the radius from the center to the edge of the Earth is going to be different depending on where or what point of the outer end of the Earth you’re going to from the center since it’s going to be longer one way than it is the other way.
Now the approximate center of the Earth is at a depth of around 6,378 kilometers. So it’s still pretty deep, but it’s the approximate center; because if you’ve got something that looks pretty spherical and you’ve got something that’s a little bit more elliptical. So if you go down this way, this is going to be a little bit longer than this is. So, depending on where you are, the distance across the Earth or through the Earth is going to be different than if you were standing 90 degrees counterclockwise or clockwise from the point on Earth where you are, if that makes sense. So basically, your approximate center would be here; but if you were traveling here, you’re going to be going a further distance than if you were going there.
So, it depends on where you are to kind of figure out the center. The point about this is just to explain that the Earth is not a perfect sphere. It is a little bit elliptical.
Now, Earth is divided into layers. And Earth’s layers consist of the crust on the outside, the mantle right underneath, and the core sometimes referred to as the inner and outer core. So it’s sometimes divided into two different layers because the center of the core is solid metal, and around that is molten liquid. And then, after that, you’ve got the mantle. So the core is actually made up of a solid part and a molten liquid part. So, the core consists of a solid inner portion surrounded by a molten outer portion. So you’ve got a solid portion in the middle and then you’ve got a molten liquid around that solid core; but that all makes up the core of the Earth.
And then you have the mantle which surrounds the core. The mantle consists of an upper solid layer which is going to be further away from the center and a lower molten or liquid layer. It’s closer to the core. So you’ve got the lower layer of the mantle and then the upper layer, which is solid.
Now the crust is the rocky, outer layer of the Earth. The crust is actually what we walk on. That is the crust. The crust is much thinner than the other layers compared to how far down the mantle and the core go. The crust is very thin compared to this. Now it’s still several miles deep, but it’s much thinner than the mantle or the core. Now, there are a couple of other terms you need to know where some of the layers of the Earth are grouped. First, you have the lithosphere. The lithosphere is made of the crust, which is on the outside, and the upper mantle, which is the solid part. It is relatively rigid. Remember the solid upper part of the mantle is made up of rock. It’s solid. It is known as the rocky sphere and it is more rigid. As a whole, the crust and the upper mantle make up that solid, more rigid, rocky sphere known as the lithosphere.
And then we have the asthenosphere. The asthenosphere is made up of the lower mantle. So it’s still all mantle, not part of the core; but the lower mantle, that’s the liquid molten part, is the asthenosphere. And it resembles a thick liquid. Think about cough syrup or honey, something real thick that’s still a liquid. This is known as the weak sphere. You roughly translate it; you have “lithos” going to rock and “astheno” going to weak. So, you have your rocky sphere that is the crust and upper mantle. And then you have your weak asthenosphere that is made up of just the lower mantle, that’s the liquid part.
And that makes sense because the solid is going to be stronger where the liquid is going to be weaker. But they are both spheres that are surrounding that inner core.
Okay, let’s look at this diagram to kind of give you a picture of where all these fit in. So this is my rendition of a globe. This would be Earth, and this is like a cut out of it. So we can see right into the center of Earth. First, we have the crust, which will be everything we can see up here. And right along the edge of our cutout, we could see the crust; and it’s real thin. Then, you’ve got everything in brown here, is the mantle. So I have a dotted line dividing the upper mantle and lower mantle, but all the brown is the mantle. All this black on the edge- the real thin part, is the crust. Then we have in green, the outer core, which is the molten layer; and the orange in the middle is your inner core, which is solid. So all this together is still your core. But you’ve got the outer core and the inner core so that you can differentiate the solid from the molten.
Now, we’ve talked about how the crust and upper mantle form the lithosphere. So that’s going to be here. The lithosphere is just going to be from the crust through the upper mantle- the solid, rigid sphere that is surrounding the center of the Earth. Then we have the lower mantle where the solid part of the mantle stops to where you get to the core; you have the asthenosphere, which is the weak sphere. So you’ve got your solid rocky lithosphere, your weaker liquid asthenosphere; and then in the middle, you’ve got your core.
So, these are the layers of the Earth. It’s important to remember each of them; because anytime we talk about the structure of the Earth, you’re going to go into the different layers, what they’re made of. And you may get into more detail with that, but this at least gives you a basic idea.
And remember, the Earth is not a perfect sphere. Its diameter from pole to pole is going to be different than the diameter across the equator. And that’s about it. Just remember your different layers. You’ve got crust, mantle, outer core, the solid inner core.