Earth Layers Explained: Uncovering the Secrets of Earth's Structure from Crust to Core

From the highest peak in the world to the deepest point in the ocean, our planet is home to countless natural marvels. But have you ever wondered what lies beneath all this stunning scenery? Imagine our planet as an enormous, cosmic onion, the layered structure of the onion similar to that of our planet. In this post, we'll embark on en epic journey straight to the heart of our plane, we’ll peel back the Earth layers one by one, and we'll explore the secrets of each layer.

Which are the Earth's layers?

Earth has several layers with distinct physical and chemical characteristics. They have different compositions, dimensions, temperatures, and pressures.

Based on the different characteristics of the layers, there are two ways of dividing the Earth layers: chemically and mechanically.

Chemical classification of Earth layers

Based on the chemical composition of the layers, we have the crust as the outmost layer. Beneath the crust we have the mantle, which can be further subdivided into the upper mantle and lower mantle. Further down, below the mantle, is the planet's core.

Mechanical classification of Earth layers

When it comes to the mechanical classification of Earth’s layers, moving from outside in, we start with the lithosphere, which includes the crust and the uppermost part of the upper mantle. Below the lithosphere sits the asthenosphere, which is part of the upper mantle, followed by the mesosphere, which comprises the lower mantle. Moving deeper inside the Earth, we have the outer core, followed by the innermost part of our planet, which is the inner core.

Earth Layers Explained

The Earth's crust

The Earth's crust is the layer that lies directly beneath our feet—our home base. The crust extends to a depth of 100 km, that’s about 60 miles below Earth’s surface. It is the thinnest of all layers and the crust thickness varies depending on its location on Earth, as follows:

Oceanic crust

Under the oceans is where we find the thinnest crust, and this is called oceanic crust. It is only about 5-10 km thick (around 3 to 6 miles).

Continental crust

The thicker crust is found under the continents, where its thickness can vary between 30 and 70 km (or 19 to 44 miles). This crust is called continental crust.

The crust temperature varies from air temperature, at the surface, to about 870° C (or 1600° F) in the deeper areas of the crust.

The crust chemical composition depends on the crust type. Thus, the oceanic crust, while thinner, it is denser than the continental crust, and it consists of basalt rocks with silicon and magnesium being the most abundant elements. The continental crust is thicker, but less dense than the oceanic crust, and it is mainly formed of granite rocks, with oxygen and silicon as the most abundant elements.

Tectonic plates

The Earth's crust is divided into sections known as tectonic plates, which are in constant motion beneath us. Tectonic plates are moving, but they’re moving very slowly—only about 3 to 5 centimeters (1.2 to 2 inches) per year. Despite this continuous movement, we usually don't notice it unless an earthquake occurs. This is because the plates rest on the Earth's mantle, the layer beneath the crust, which allows them to 'float' and shift. Occasionally, this gradual movement, known as plate tectonics, triggers earthquakes and volcanic eruptions.

The Earth's mantle

The Earth's mantle is located between 100 km and 2900 km (between about 60 and 1800 miles) below the Earth’s surface. This makes the mantle the Earth’s thickest layer.

The outermost layer of the mantle is cooler and more rigid, behaving similarly to the crust above it. That’s why we can cluster these two into the mechanical layer called the lithosphere.

The deeper we go in the mantle, the hotter it gets, and it can get as hot as 4000° C as we get near the core. Besides being hotter than the crust, the mantle also has a higher pressure than the crust. And you know what forms under pressure? Diamonds! That’s right! The mantle is where diamonds are formed! If you want to learn more about diamonds, how they are formed, and how they get from the upper mantle to the Earth’s surface, then I have this other post dedicated entirely to diamonds and this post that tells you all about the diamond colors.

The deeper we go into the mantle, the higher the pressure, reaching 135 GPa (gigapasclas), or 1.3 million atmospheres closer to the core.

The mantle is a layer of hot, dense rock rich in iron, magnesium, and silicone. Although it is solid, it behaves like a thick, semi-solid material due to the immense heat and pressure conditions we now know are present in the mantle. The mantle is much denser and thicker than the crust, allowing the tectonic plates above it to “float,” and shift, occasionally leading to earthquakes. The layer of the mantle that flows and moves the plates is called the asthenosphere, and sits right below the rigid lithosphere.

The upper part of the mantle and lower part of the crust is where magma is formed.

The rest of the mantle that’s below the asthenosphere is the called the mesosphere, and it is more rigid than the asthenosphere.

The Earth's core

The Earth's outer core and inner core

Our planet’s core is divided into the outer core, right below the mantle expanding between 2900 and 5100 km (or roughly 1800 to 3200 miles), and the inner core, located between the depths of 5100 and 6378 km, or roughly 3200 to 3960 miles.

Both the outer core and the inner core have similar compositions, being composed mainly of iron and nickel. However, despite their similarities in composition, these two layers are very different because of the different pressure and temperature conditions in these layers.

The outer core has a much higher density and temperature than the mantle. The temperatures here vary between 4,030° C (or 7,280° F) closer to the mantle to 5,730° C (or 10,340° F) closer to the inner core. The pressure in the outer core ranges between 135 and 330 GPa (1.3-3.3 million atmospheres). While these are huge pressures, they’re still much lower than the pressure in the inner core, which goes up to 330 to 360 GPa (3.3-3.6 million atmospheres). And it’s these high pressures that keep the inner core solid, while the material in the outer core is a low viscosity fluid.

This fluid layer undergoes turbulent convection and rotates faster than the rest of the planet, generating eddy currents in the molten metal-rich fluid core. This creates a dynamo effect, which is believed to be the cause of Earth's magnetic field.

The Earth's inner-inner core

Recent studies indicate that the Earth's inner core also has a layered structure, with the possible existence of an inner-inner core, possibly composed of iron in a different crystal form than that of the rest of the inner core. But more research needs to be done to understand this better.

Isn’t it fun how the new developments in science can help us learn more and more about our planet?!

The deepest man-made hole in Earth's crust

How deep inside our planet do you think humans were able to reach? It's not that deep at all...

The deepest hole humans have ever dug into Earth is the Kola Superdeep Borehole in the Kola Peninsula in northwestern Russia, near the Russian border with Norway. This is the deepest man-made hole on Earth and it reaches a depth of 12,262 meters (or 40230 feet). Considering the continental crust reaches a depth of 100 km, this remarkable achievement shows just how much more of our planet remains unexplored.

I'm looking forward to future developments in scientific techniques that will allow us to learn even more about the Earth layers and our planet's deep secrets.