The planet can be divided into 4 main layers: the solid crust on the outside, the mantle, the outer core and the inner core. Out of them, the tardy is the thinnest layer of the Earth, amounting for less than 1% of our planet's volume.

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byMihai Andrei

The planet can be separated into 4 main layers: the solid tardy on the outside, the mantle, the outer core and the inner core. Out of them, the crust is the thinnest layer of the Earth, amounting for less than 1% of our planet’s volume.

The Earth’s structure

Artistic depiction of the Earth’s structure. Picture via Victoria Museum.

The Earth’s structure can be share in two means – based on mechanical properties, and based ~ above the chemistry. Here, we’re simply going to discuss a simple classification, without going right into most details. The main emphasis here is come understand how the Earth’s crust really is, and also why it is the thinnest layer.

The crust ranges from5–70 kilometres (~3–44 miles) in depth and is the outermost layer. The thinnest parts are oceanic crust, when the thicker components are continental crust. Most rocks in ~ the Earth’s surface are reasonably young (less 보다 100 million years old, compared to the Earth’s age, i m sorry is around 4,4 billion years), but because we uncovered some rocks i beg your pardon are lot older, we know that earth has had actually a solid crust because that at the very least 4.4 billion years.The mantleextends from wherein the crust ends to about2,890 km, making that the thickest great of Earth. The mantle is additionally composed the silicate rocks, however the mantle as a entirety is an extremely viscous – the high temperatures therecause the silicate material to be sufficiently ductile the it can flow (in a very long time). The mantle is generally divided intothe upper and also the reduced mantle.The core, generally divided intotheouter core and also theinner core. The external core is concerned as viscous, despite much much less so 보다 the mantle, when the inner core is solid.Schematic check out of the interior of Earth. 1. Continental crust – 2. Oceanic late – 3. Upper mantle – 4. Reduced 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 crust is top top average around 40 km deep – which is much thinner than the mantle, the external core and also the inner main point – you can think the it prefer the peel of an apple. The late here has actually been created through igneous processes, which describes why the crust has much more incompatible elements than the mantle.


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Oceanic vs continent crust. Picture via USGS.

At the bottom of the oceans and also some seas, over there is oceanic crust. Oceanic tardy is an extremely thin (usually under 10 km), and also is written of dense, generally dark (mafic) rocks: basalt, gabbro, diabase. The continent crust is thicker 보다 that – generally it’s roughly 40 kilometres deep, yet can go up to 70. The two types of late are likewise sometimes dubbed granitic (continental) and basaltic (oceanic).

The crust is no one strictly layer, however is damaged into fifteen tectonic plates, all in relative movement one come the other. This is called an international tectonics. The plates themselves space thicker than the tardy alone, and also consist that the shallow mantle in ~ the crust – this together is called the litosphere. The late is where rocks connect with the hydrosphere and much more importantly, the atmosphere. Brand-new rocks, minerals and also materials are formed here. Here’s the crucial part: all of the range and phenomena the we can see v our very own eyes take place in the crust. Everything, indigenous mining ores come oil to developing mountains to thick deposits, faults and also whatever you ever heard about geologists observing straight takes location inside the crust (or at the an extremely surface). The deepest drill ever before is simply over 12 km, and also we won’t be seeing the bottom that the crust v our very own eyes because that a really long time.

How us know

OK, therefore there’s a crust, it’s thin, there’s additionally a mantle and also a core… however if us can’t walk there, just how do us know?


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


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Waves propagating native Earthquakes through the Earth. Photo via Brisith geology Survey.

A century ago, human being didn’t recognize the planet had a crust. Part theoretized it did, yet there to be very tiny proof. The very first clues came from astronomic indications, however most of what we understand today around the Earth’s structure comes from seismological observations.Seismic tide from huge earthquakes pass throughout the Earth, and also they carry with them information from the settings they happen through. Similar to rays of light, seismic waves deserve to reflect, refract and diffract.Because the rate of the seismic waves counts on density, we deserve to use the travel-time the seismic waves to map readjust in thickness with depth. Also, because some waves just propagate v solid environments, we understand that some atmospheres (like the the external core) areviscous– since the tide don’t propagate v them.

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

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Mihai Andrei

Andrei"s background is in geophysics, and also he"s to be fascinated by it ever because he was a child. Feeling that there is a gap in between scientists and the general audience, he started ZME science -- and also the results are what you view today.