The planet can be separated into four main layers: the solid tardy on the outside, the mantle, the outer core and the inner core. The end of them, the tardy is the thinnest class of the Earth, amounting for less than 1% of our planet's volume.

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byMihai Andrei

The earth can be divided into 4 main layers: the solid late on the outside, the mantle, the external core and the inside core. The end of them, the crust is the thinnest great of the Earth, amounting for less than 1% of ours planet’s volume.

The Earth’s structure

Artistic explicate of the Earth’s structure. Photo via Victoria Museum.

The Earth’s structure have the right to be divide in two ways – based upon mechanical properties, and based top top the chemistry. Here, we’re simply going to talk about a basic classification, there is no going into most details. The main focus here is to understand just how the Earth’s crust really is, and why it is the thinnest layer.

The crust varieties from5–70 km (~3–44 miles) in depth and is the outermost layer. The thinnest components are oceanic crust, while the thicker parts are continental crust. Most rocks in ~ the Earth’s surface ar are reasonably young (less 보다 100 million year old, compared to the Earth’s age, i beg your pardon is approximately 4,4 exchange rate years), but because we found some rocks i beg your pardon are much older, we recognize that earth has had a hard crust because that at least 4.4 exchange rate years.The mantleextends from wherein the crust ends to about2,890 km, making it the thickest class of Earth. The mantle is likewise composed that silicate rocks, but the mantle as a whole is very viscous – the high temperature therecause the silicate material to be saturated ductile the it can flow (in a an extremely long time). The mantle is generally separated intothe upper and also the reduced mantle.The core, frequently divided intotheouter core and theinner core. The external core is pertained to as viscous, despite much less so 보다 the mantle, when the inner main point is solid.Schematic see of the interior of Earth. 1. Continental crust – 2. Oceanic tardy – 3. Top mantle – 4. Lower mantle – 5. Outer core – 6. Inner main point – A: Mohorovičić discontinuity – B: Gutenberg Discontinuity – C: Lehmann–Bullen discontinuity.

The Earth’s crust

Our planet’s late is top top average around 40 km deep – i beg your pardon is lot thinner 보다 the mantle, the external core and also the inner main point – you have the right to think of it like the peel of an apple. The late here has been created through igneous processes, which describes why the crust has actually much much more incompatible elements than the mantle.


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Oceanic vs continental crust. Picture via USGS.

At the bottom the the oceans and some seas, over there is oceanic crust. Oceanic crust is really thin (usually under 10 km), and also is created of dense, commonly dark (mafic) rocks: basalt, gabbro, diabase. The continent crust is thicker 보다 that – usually it’s approximately 40 kilometres deep, but can go as much as 70. The two types of late are likewise sometimes called granitic (continental) and basaltic (oceanic).


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The crust is no one rigid layer, but is damaged into fifteen tectonic plates, every in relative motion one come the other. This is called global tectonics. The plates themselves are thicker 보다 the crust alone, and also consist of the shallow mantle beneath the crust – this together is called the litosphere. The tardy is whereby rocks connect with the hydrosphere and an ext importantly, the atmosphere. New rocks, minerals and materials are developed here. Here’s the important part: every one of the selection and phenomena that we have the right to see with our own eyes take place in the crust. Everything, from mining ores to oil to forming mountains to thick deposits, faults and also whatever you ever before heard around geologists observing straight takes location inside the late (or at the really surface). The deepest drill ever before is just over 12 km, and we won’t be seeing the bottom of the crust through our own eyes for a an extremely long time.

How we know

OK, for this reason there’s a crust, it’s thin, there’s also a mantle and also a core… but if us can’t go there, exactly how do us know?


That’s a very an excellent question – but this is where scientific research comes in. Us know every one of this (and we recognize it v a really high degree of confidence) with indirect observation.

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Waves propagating from Earthquakes with the Earth. Picture via Brisith geological Survey.

A century ago, world didn’t know the planet had a crust. Part theoretized the did, yet there was very tiny proof. The first clues came from astronomic indications, but most the what we understand today about the Earth’s structure comes from seismological observations.Seismic tide from large earthquakes pass throughout the Earth, and also they bring with them info from the settings they happen through. Similar to rays of light, seismic waves have the right to reflect, refract and diffract.Because the rate of the seismic waves depends on density, we deserve to use the travel-time that seismic waves to map adjust in thickness with depth. Also, due to the fact that some waves just propagate through solid environments, we recognize that some atmospheres (like the the outer core) areviscous– due to the fact that the waves don’t propagate with them.

In 1909, the brilliant seismologist Andrija Mohorovicic foundthat around 50 kilometers deep in the earth there is a sudden readjust in seismic velocity – and also knew the it should be a very far-ranging discontinuity. He also observed that seismic tide reflect and refract at the depth, which confirmed his ideas.That discontinuity, named todaythe Mohorovicic discontinuity (or merely “Moho”) is regarded today together the limit between the crust and also the mantle.

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Mihai Andrei

Andrei"s elevator is in geophysics, and he"s been fascinated by the ever since he was a child. Emotion that there is a gap between scientists and the basic audience, he began ZME science -- and the outcomes are what you see today.