The layers of our planet are some of its most interesting features. You can learn a lot about your neighborhood by studying the planets interior structure. For example, you would know that the inner part of the earth is solid, whereas the outer layer is liquid.
You also get an idea of how much pressure there is in the center of the planet due to all of the matter packed together. This pressure comes from two sources; gravity and internal temperature.
When a meteor hits the surface it creates lots of heat which causes the rock to melt and run down as lava. Some of this molten material then cools and hardens into new minerals creating more compartments for energy storage.
The inner core is made of solid iron, while the outer layer is liquid. Between these two layers is another fluid called magma. As we will see in the next section, this magma comes from melting parts of the mantle!
The top surface of the earth is very hot because heat is constantly flowing into it from the sun. This heat flows down through our planet’s interior via conduction (when particles vibrate with energy) and convection (when fluids such as water or molten material are displaced by internal movements).
As temperature decreases towards the centre of the earth, different minerals become more stable and so form a rock. For example, some crystals of magnesium form denser solid shapes when cooled to colder temperatures. Magnesium makes up about 0.1% of all the atoms in the earth’s crust, making it one of its most abundant elements.
So what happens to the leftover magnesium? It dissolves in the liquid that now occupies your place at the bottom of the earth! This new phase of matter is referred to as ‘magmatic fluid’. Some scientists also refer to it as ‘melt’ but that term can be confusing as it sometimes refers to any melted substance you find anywhere within a planetary body.
Magmatic fluid circulates throughout the lower part of the earth’s interior, interacting with other liquids and gases present there.
The outer layer of our planet is called its crust. You may have heard people refer to the “solid part” of the earth, but this isn’t quite right!
The word solid doesn’t describe the crust well. We should be more specific by saying “compact” or “dense” instead because the interior of the earth is actually very empty. It contains lots of space which are some of the most important ingredients for life as we know it.
You can think about water as another good example. There is not much water inside an apple, but if you took away all the air from an apple then there would be nothing left- no space in which water could form. Similarly, the inner parts of the earth are full of oxygen and other elements that play a key role in creating living things.
So what does make up the crust? That depends on where you look! If you take a piece of the ocean floor, for instance, you will probably find mostly made up of granite. This is due to repeated heating and cooling of the rocks in the mantle (the place between the crust and the core) under the influence of convection currents and magma rising towards the surface. As these hot liquids come into contact with cold rock, they cause it to melt and eventually rise to the surface as lava.
We, as humans, spend a lot of time thinking about how deep down there are layers in the earth’s crust, but we rarely think about what kind of layer we are talking about.
We use terms like “mantle” or “solid crust” to describe the layer that extends very few inches below the surface, but they are not truly descriptive.
The word “crust” is misleading because it implies something solid instead of fluid. A more accurate term would be “lava flow deposit.” This is an extremely viscous liquid that can sometimes gush forth violently from beneath the surface.
This happened during the eruption of Mount St. Helens back in 1980. It took almost two weeks for everything was fully resolved due to the thickness of the hardened lava. Scientists now refer to this thickened lava as a “pluton.
The mantle convection
The inner part of the earth is made up of three different layers: the outer layer, which we refer to as the crust; the middle layer, or mantle; and then an even more internal layer called the solidified core.
The crust is the most well-known layer of our planet because it is this layer that makes up the surface. You are probably very familiar with at least some portion of the crust, such as what is referred to as the “mantle” (the interior material just below the crust). This term comes from how scientists thought the planets were formed: they hypothesize that there was a hot molten mass in space, and as time passed, gravity caused parts of this mass to clump together into larger lumps. Some of these lumps cooled down enough to form a hard, rocky shell around the nucleus, and so those shells got labeled as being part of the crust.
But now we know that this hypothesis is not correct! We know that the early solar system had a lot of gasses in it, and over time, many of these gases condensed to make new stars. And we also know that some of the matter from these newly created stars eventually settled down to become the next stage of planetary growth: the formation of the other two major layers of the earth.
In fact, one theory about why geologists think the moon originally had no atmosphere is due to rising temperatures causing the lunar mantle to melt and flow away.
The mantle structure
The inner core is made up of solid iron, while the outer layer is liquid. Between these two layers are five major regions. These include the lithosphere (solid crust), asthenosphere (fissured or broken crust), lower mantle, upper mantle and the core.
The lowermost part of the mantle is called the lithospheric mantle. This is what we refer to as the “crust” that covers our planet. It consists mostly of silicate minerals such as feldspars and pyroxenes.
The next region up is referred to as the asthenospheric mantle. This is characterized by magnesium-rich olivine and pyroxene crystals mixed in with the more typical silica ones.
Next comes the transition zone, which makes up about one third of the thickness of the mantle. It is comprised almost entirely of potassium and sodium salts.
Above this lies the convective zone, which contains most of the volume of the mantle. In here, there are plate tectonics happening! Plates move around due to differences in density caused by variations in composition.
And lastly, we have the core, which is completely composed of pure nickel and iron. Scientists believe that it formed early in planetary history when heavier elements settled into the center of the protoplanet.
Given how much time has passed since then, though, no direct evidence of the formation process of the core exists.
The center of our planet is something we know little about, even though it makes up almost half of our world! We have very few clues as to what kind of material it is or how solid it is. It is thought to be mostly liquid but there are some theories that it is actually gaseous.
The hypothesis most scientists agree with is that the inner part of our planet is made up of iron, nickel, and silicate minerals such as olivine. These materials form when gas molecules combine together and condense into solids.
If this was true then over time, the pressure from all these layers would compress the outer parts of the planet and cause it to get thinner. This does not seem likely since we have evidence that the entire planet has been stable for at least the last several billion years.
Another theory suggests that the interior of the earth might be completely fluid instead of being solid like current thinking implies. If this were true then the whole thing could potentially melt down and run off as lava. However, this seems unlikely too because if this happened the surface layer would also be melted and mixed in with the magma which it is not.
The tectonic plates
As mentioned earlier, plate tectonics is what causes earthquakes and volcanic activity. Plate tectonics also affects our weather and environment. When two plates collide, it can unleash an explosion of energy. This happens when magma from inside of the planet comes in contact with water or dry land!
The process of collision starts off as slow moving movement then suddenly speeds up until one of the two layers breaks away and becomes a new chunk of crust for the planet to form into.
Another major layer of our planet is the denser part, or material, that makes up its surface. This layer is called the lithospheric mantle.
The lithopoic mantle makes up some 70 percent of the earth’s volume. It is mostly made up of solid iron and nickel oxides (oxidation states 9 to 11) with small amounts of magnesium and calcium. These minerals are mixed in a liquid state.
By contrast, the upper 30% of the interior is composed of silicate rocks such as granite and quartz. These materials can be melted down to form new crystals, which then rise to the surface as volcanism occurs.
We will not go into detail about how these layers interact with each other nor do we need to know what each one does, but it is important to understand their relationship because they determine where most volcanic activity happens.
How deep the lithospheric mantle goes within the earth depends largely on two things: temperature and pressure. As the inner core cools and shrinks, it gets thinner and more mobile. When this occurs, there is greater interaction between the outermost parts of the lithotipgic mantle and the underlying hot, fluid-like material.
This may result in magma being drawn upward towards the surface.