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The earth has a spherical structure, which was deduced by a geologist from Austria Suess over a hundred years ago. However, only modern measurement methods, e.g. seismic waves, could confirm his suppositions.
Petrologic criterion
The simplest division of the Earth’s interior is according to the petrological criterion (takes into account the chemical composition of rocks):
- Earth’s crust
- Earth’s mantle
- Earth’s core
Earth’s crust covers 1.4% of the globe’s volume and 0.3% of its mass. It reaches from 5 to 80 km deep into the planet.
According to the old division, its outer part is granite SIAL (Si – silicon, Al – aluminium sulfate), and the inner part is basalt-hump SIMA (Si – silicon, Mg – magnesium). Between them is the Conrad discontinuity.
The new division speaks of the continental crust (35-80 km deep), oceanic (5-8 km from the bottom) and the transition between them. Due to the high variability in the thickness of crust elements and many geological factors, discontinuity surfaces are not taken into account, because they do not always occur or are at different depths.
The oceanic crust consists mainly of basalts and, depending on the shape of the bottom, of varying thickness of sediments. The continental crust is a little more complicated. On the surface, it consists of granites and gneisses (formerly SIAL), below of quartz diorites and enderbits, and at the bottom of gabs, diorites and amphibolites (former SIMA). There are also settlements.
The division into shields, platforms, forming cratons and orogens should also be distinguished.
Cratons is a rigid part of the shell that does not deform. If there are deposits on its parts, then it is a platform, if there are no deposits or the layer is minimal, we call it a shield. Orogens are fragments of the crust that have grown in orogenesis.
Between the shell and mantle Mohorovičić discontinuity (Moho) extends, on average 33 km deep. At this point, seismic waves rapidly increase speed.
Earth’s mantle is 82.6% by volume and 68.3% by mass of our planet. It is located on average between 33 and 2700 km deep. It is built mainly of peridotite and the lower it has larger admixtures of heavy metals.
It is divided into upper mantles ( CROFESIMA – Cr – chromium, Fe – iron, Si – silicon, Mg – magnesium) and lower mantle (NIFESIMA – Ni – nickel, Fe – iron, Si – silicon, Mg – magnesium). Between them Repetti discontinuity, up to 600 km thick.
Eart’s core and mantel are separated the Wiechert-Gutenberg discontinuity, also known as the core-mantle boundary (CMB). In this sphere, there is a sharp jump in rock density. The core contains 16% volume and 31.4% of the Earth’s mass. It begins at a depth of about 2900 km. Another name is NIFE (Nickel, Fe – iron), given by Suess. Rocks are liquid or semi-liquid.
Earth’s outer core is about 2000 km thick, followed by the Lehman discontinuity and the inner core.
Rheological criterion
Another division criterion is rheological, i.e. one that takes into account the physical properties of rocks. And so in turn, we distinguish:
- lithosphere
- asthenosphere
- mesosphere
- outer core
- inner core
As you can see, the difference occurs in the two upper layers – the shell and the mantle.
The lithosphere extends to the entire crust and a fragment of the mantle called the peritotide layer. Under the oceans, it reaches 80-100 km deep into the Earth, under continents 200-250 km.
The next layer is the semi-plastic asthenosphere. It extends until the surface of Golycin discontinuity occurring at a depth of 350-400 km.
Below is the mesosphere ending with the Wiechert-Gutenberg discontinuity .
| petrological criterion | rheological criterion | ||
|---|---|---|---|
|
Earth’s crust
|
SIAL
|
oceanic crust
transitional crust continental crust |
lithosphere
|
|
Conrad discontinuity
|
|||
|
SIMA
|
|||
|
Moho discontinuity
|
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|
Earth’s mantle
|
upper mantle(CROFESIMA)
|
peridotite layer
|
|
|
asthenosphere
|
|||
|
Golicyn discontinuity
|
|||
|
mesosphere
|
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|
Repetti discontinuity
|
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|
lower mantle (NIFESIMA)
|
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|
Wiechert-Gutenberg discontinuity
|
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|
Earth’s core (NIFE)
|
outer core
|
||
|
Lehman discontinuity
|
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|
inner core
|
|||
The pressure inside the Earth increases steadily – closer to the surface slower, from Golycin discontinuities faster. In the crust, it reaches 0.9-1.4 GPa, in the jacket 1.4-40 GPa, in the surface of Wiechert-Gutenberg discontinuity 120-150 GPa, in the outer core 150-320 GPa and internal up to 400 GPa.
The temperature also increases steadily – the fastest in the lithosphere and asthenosphere, the slowest in the nucleus.
In the lithosphere up to 1000 degrees Celsius, in the asthenosphere up to 1600 degrees, in the transitional sphere of Wiechert-Gutenberg up to 4500 degrees, Lehman up to 6000 degrees, and in the internal core over 6000 degrees.
