Structure of Earth

1.

2.

3.

4.

Earth - Земля
[ɜːθ]
Atmosphere -
[ˈætməsfɪə]
атмосфера
Hydrosphere гидросфера
[ˈhaɪdrəsfɪə]

5.

Asthenosphere -
[əsˈθiːnəsfɪə]
астеносфера
mantle - мантия
[mæntl]
outer core - внешнее
[ˈaʊtə kɔː]
ядро

6.

Earth's magnetic field -
[ɜːθ'es mægˈnetɪk fiːld]
магнитное поле Земли
inner core - внутреннее
[ˈɪnə kɔː]
ядро
Lithosphere литосфера
[ˈlɪθəsfɪə]

7.

lower mantle - нижняя
мантия
[ˈləʊə mæntl]

8.

Earth

9.

The internal structure of Earth, structure of the solid Earth, or simply structure of
Earth refers to concentric spherical layers subdividing the Solid earth, i.e., excluding
Earth's atmosphere and hydrosphere. It consists of an outer silicate solid crust, a
highly viscous asthenosphere and solid mantle, a liquid outer core whose flow
generates the Earth's magnetic field, and a solid inner core.
Scientific understanding of the internal structure of Earth is based on observations of
topography and bathymetry, observations of rock in outcrop, samples brought to the
surface from greater depths by volcanoes or volcanic activity, analysis of the seismic
waves that pass through Earth, measurements of the gravitational and magnetic fields
of Earth, and experiments with crystalline solids at pressures and temperatures
characteristic of Earth's deep interior.
The structure of Earth can be defined in two ways: by mechanical properties such as
rheology, or chemically. Mechanically, it can be divided into lithosphere,
asthenosphere, mesospheric mantle, outer core, and the inner core. Chemically, Earth
can be divided into the crust, upper mantle, lower mantle, outer core, and inner core.
The geologic component layers of Earth are at the following depths below the surface.
The layering of Earth has been inferred indirectly using the time of travel of refracted
and reflected seismic waves created by earthquakes. The core does not allow shear
waves to pass through it, while the speed of travel (seismic velocity) is different in
other layers. The changes in seismic velocity between different layers causes
refraction owing to Snell's law, like light bending as it passes through a prism.

10.

Atmosphere

11.

The atmosphere of Earth, commonly known as air, is the layer of gases retained by
Earth's gravity that surrounds the planet and forms its planetary atmosphere. The
atmosphere of Earth protects life on Earth by creating pressure allowing for liquid
water to exist on the Earth's surface, absorbing ultraviolet solar radiation, warming
the surface through heat retention (greenhouse effect), and reducing temperature
extremes between day and night (the diurnal temperature variation).
By volume, dry air contains 78.08% nitrogen, 20.95% oxygen, 0.93% argon, 0.04%
carbon dioxide, and small amounts of other gases. Air also contains a variable amount
of water vapor, on average around 1% at sea level, and 0.4% over the entire
atmosphere. Air composition, temperature, and atmospheric pressure vary with
altitude. Within the atmosphere, air suitable for use in photosynthesis by terrestrial
plants and breathing of terrestrial animals is found only in Earth's troposphere.
Earth's early atmosphere consisted of gases in the solar nebula, primarily hydrogen.
The atmosphere changed significantly over time, affected by many factors such as
volcanism, life, and weathering. Recently, human activity has also contributed to
atmospheric changes, such as global warming, ozone depletion and acid deposition.

12.

Hydrosphere

13.

The hydrosphere is the combined mass of water found on, under, and above the
surface of a planet, minor planet, or natural satellite. Although Earth's hydrosphere
has been around for about 4 billion years, it continues to change in shape. This is
caused by seafloor spreading and continental drift, which rearranges the land and
ocean.
It has been estimated that there are 1.36 billion cubic kilometers (332 million cubic
miles) of water on Earth. This includes water in liquid and frozen forms in
groundwater, oceans, lakes and streams. Saltwater accounts for 97.5% of this amount,
whereas fresh water accounts for only 2.5%. Of this fresh water, 68.9% is in the form
of ice and permanent snow cover in the Arctic, the Antarctic and mountain glaciers;
30.8% is in the form of fresh groundwater; and only 0.3% of the fresh water on Earth
is in easily accessible lakes, reservoirs and river systems.
The total mass of Earth's hydrosphere is about 1.4 × 1018 tonnes, which is about
0.023% of Earth's total mass. At any given time, about 20 × 1012 tonnes of this is in the
form of water vapor in the Earth's atmosphere (for practical purposes, 1 cubic meter of
water weighs one tonne). Approximately 71% of Earth's surface, an area of some 361
million square kilometers, is covered by ocean. The average salinity of Earth's oceans
is about 35 grams of salt per kilogram of sea water (3.5%).

14.

Asthenosphere

15.

The asthenosphere is the highly viscous, mechanically weak, and ductile region of
the upper mantle of Earth. It lies below the lithosphere, at depths between
approximately 80 and 200 km below the surface. The lithosphere–asthenosphere
boundary is usually referred to as LAB. The asthenosphere is almost solid, although
some of its regions could be molten (e.g., below mid-ocean ridges). The lower
boundary of the asthenosphere is not well defined. The thickness of the
asthenosphere depends mainly on the temperature. However, the rheology of the
asthenosphere also depends on the rate of deformation, which suggests that the
asthenosphere could be also formed as a result of a high rate of deformation. In some
regions, the asthenosphere could extend as deep as 700 km. It is considered the source
region of mid-ocean ridge basalt.
The asthenosphere is a part of the upper mantle just below the lithosphere that is
involved in plate tectonic movement and isostatic adjustments. The lithosphereasthenosphere boundary is conventionally taken at the 1300 °C isotherm. Below this
temperature (closer to the surface) the mantle behaves rigidly; above this temperature
(deeper below the surface) it acts in a ductile fashion.
Seismic waves pass relatively slowly through the asthenosphere compared to the
overlying lithospheric mantle, thus it has been called the low-velocity zone, although
the two are not the same. This was the observation that originally alerted
seismologists to its presence and gave some information about its physical properties,
as the speed of seismic waves decreases with decreasing rigidity.

16.

Mantle

17.

A mantle is a layer inside a planetary body bounded below by a core and above by a
crust. Mantles are made of rock or ices, and are generally the largest and most massive
layer of the planetary body. Mantles are characteristic of planetary bodies that have
undergone differentiation by density. All terrestrial planets (including Earth), a
number of asteroids, and some planetary moons have mantles.
The Earth's mantle is a layer of silicate rock between the crust and the outer core. Its
mass of 4.01 × 1024 kg is 67% the mass of the Earth. It has a thickness of 2,900
kilometres making up about 84% of Earth's volume. It is predominantly solid but in
geological time it behaves as a viscous fluid. Partial melting of the mantle at midocean ridges produces oceanic crust, and partial melting of the mantle at subduction
zones produces continental crust.

18.

Outer core

19.

Earth's outer core is a fluid layer about 2,400 km thick and composed of mostly iron
and nickel that lies above Earth's solid inner core and below its mantle. Its outer
boundary lies 2,890 km beneath Earth's surface. The transition between the inner core
and outer core is located approximately 5,150 km beneath the Earth's surface. Unlike
the inner (or solid) core, the outer core is liquid.
Seismic inversions of body waves and normal modes constrain the radius of the outer
core to be 3483 km with an uncertainty of 5 km, while that of the inner core is 1220±10
km.
Estimates for the temperature of the outer core are about 3,000–4,500 K in its outer
region and 4,000–8,000 K near the inner core. Evidence for a fluid outer core includes
seismology which shows that seismic shear-waves are not transmitted through the
outer core. Because of its high temperature, modeling work has shown that the outer
core is a low-viscosity fluid that convects turbulently. The dynamo theory sees eddy
currents in the nickel–iron fluid of the outer core as principal source of the Earth's
magnetic field. The average magnetic field strength in the Earth's outer core is
estimated to be 2.5 millitesla, 50 times stronger than the magnetic field at the surface.
The outer core is not under enough pressure to be solid, so it is liquid even though it
has a composition similar to the inner core. Sulfur and oxygen could be present in the
outer core. As heat is transferred outward toward the mantle, the net trend is for the
inner boundary of the liquid region to freeze, causing the solid inner core to grow at
expense of the outer core, at an estimated rate of 1 mm per year.

20.

Earth's magnetic field

21.

Earth's magnetic field, also known as the geomagnetic field, is the magnetic field that
extends from the Earth's interior out into space, where it interacts with the solar wind,
a stream of charged particles emanating from the Sun. The magnetic field is
generated by electric currents due to the motion of convection currents of a mixture of
molten iron and nickel in the Earth's outer core: these convection currents are caused
by heat escaping from the core, a natural process called a geodynamo. The magnitude
of the Earth's magnetic field at its surface ranges from 25 to 65 μT. As an
approximation, it is represented by a field of a magnetic dipole currently tilted at an
angle of about 11 degrees with respect to Earth's rotational axis, as if there were an
enormous bar magnet placed at that angle through the center of the Earth. The North
geomagnetic pole actually represents the South pole of the Earth's magnetic field, and
conversely the South geomagnetic pole corresponds to the north pole of Earth's
magnetic field (because opposite magnetic poles attract and the north end of a
magnet, like a compass needle, points toward the Earth's South magnetic field, i.e.,
the North geomagnetic pole near the Geographic North Pole). As of 2015, the North
geomagnetic pole was located on Ellesmere Island, Nunavut, Canada.
While the North and South magnetic poles are usually located near the geographic
poles, they slowly and continuously move over geological time scales, but sufficiently
slowly for ordinary compasses to remain useful for navigation. However, at irregular
intervals averaging several hundred thousand years, the Earth's field reverses and the
North and South Magnetic Poles respectively, abruptly switch places. These reversals
of the geomagnetic poles leave a record in rocks that are of value to paleomagnetists
in calculating geomagnetic fields in the past.

22.

Inner core

23.

Earth's inner core is the innermost geologic layer of the planet Earth. It is primarily a
solid ball with a radius of about 1,220 km, which is about 20% of Earth's radius or
70% of the Moon's radius.
There are no samples of Earth's core accessible for direct measurement, as there are
for Earth's mantle. Information about Earth's core mostly comes from analysis of
seismic waves and Earth's magnetic field. The inner core is believed to be composed
of an iron–nickel alloy with some other elements. The temperature at the inner core's
surface is estimated to be approximately 5,700 K, which is about the temperature at
the surface of the Sun.

24.

Lithosphere

25.

A lithosphere is the rigid, outermost shell of a terrestrial-type planet or natural
satellite. On Earth, it is composed of the crust and the portion of the upper mantle
that behaves elastically on time scales of thousands of years or greater. The crust and
upper mantle are distinguished on the basis of chemistry and mineralogy.
Earth's lithosphere includes the crust and the uppermost mantle, which constitutes
the hard and rigid outer layer of the Earth. The lithosphere is subdivided into tectonic
plates. The lithosphere is underlain by the asthenosphere which is the weaker, hotter,
and deeper part of the upper mantle. The Lithosphere-Asthenosphere boundary is
defined by a difference in response to stress: the lithosphere remains rigid for very
long periods of geologic time in which it deforms elastically and through brittle
failure, while the asthenosphere deforms viscously and accommodates strain through
plastic deformation.
The thickness of the lithosphere is thus considered to be the depth to the isotherm
associated with the transition between brittle and viscous behavior. The temperature
at which olivine becomes ductile is often used to set this isotherm because olivine is
generally the weakest mineral in the upper mantle.

26.

Lower mantle

27.

The lower mantle, historically also known as the mesosphere, represents
approximately 56% of Earth's total volume, and is the region from 660 to 2900 km
below Earth's surface; between the transition zone and the outer core. The
preliminary reference Earth model separates the lower mantle into three sections, the
uppermost, mid-lower mantle, and the D layer. Pressure and temperature in the lower
mantle range from 24–127 Gpa and 1900–2600 K. It has been proposed that the
composition of the lower mantle is pyrolitic, containing three major phases of
bridgmanite, ferropericlase, and calcium-silicate perovskite. The high pressure in the
lower mantle has been shown to induce a spin transition of iron-bearing bridgmanite
and ferropericlase, which may affect both mantle plume dynamics and lower mantle
chemistry.
The upper boundary is defined by the sharp increase in seismic wave velocities and
density at a depth of 660 kilometers. At a depth of 660 km, ringwoodite (γ-(Mg,Fe)
2SiO4) decomposes into Mg-Si perovskite and magnesiowüstite. This reaction marks
the boundary between the upper mantle and lower mantle. This measurement is
estimated from seismic data and high-pressure laboratory experiments. The base of
the mesosphere includes the D″ zone which lies just above the mantle–core boundary
at approximately 2,700 to 2,890 km. The base of the lower mantle is about 2700 km.