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Earth in the Universe
21
Observations, that had been made by three different astronomers by the
19th century, helped us to draw conclusions about the nature of the Solar System
and its place in the Universe. At first, we should mention the measurement of the
apparent displacement of the position of the star made by astronomer Friedrich
Bessel in 1839. He came to the conclusion that that phenomenon was caused by
the movement of Earth around the Sun (aka stellar parallax). That not only undoubtedly confirmed that there was the heliocentric model, but also found the huge
distance between the stars and the Sun. In 1859, Robert Bunsen and Gustav Kirchhoff (a German chemist and physicist) used a newly invented spectroscope to
study the spectral signature of the Sun. They discovered that it consisted of the
same elements that existed on Earth, thereby proving that Earth and other celestial
bodies consisted of the same elements.
Structure and composition:
The Sun (main sequence star G2) is in the center of the Solar System; it is
surrounded by four terrestrial planets (Inner Planets), the main asteroid Belt,
four gas giants (Outer Planets), a massive field of small bodies that extends
from 30 to 50 A.U. from the Sun (Kuiper Belt). Further, the system is surrounded by a spherical cloud of icy comets (the Oort cloud), which is believed
to extend to a distance of 100,000 A.U. from the Sun into the Interstellar medium (Kostyukova, Mikhailenko, 2011).
The sun contains 99,86 % of the known mass of the system, and its gravity
dominates the entire system. The largest objects in the orbit around the Sun
lie near the plane of the Earth's orbit (the ecliptic), and most of the planets
and bodies rotate around it in the same direction (counterclockwise, if viewed
from above at the North Pole of the Earth). Planets are very close to the
ecliptic, while comets and the Kuiper Belt objects are often at a large angle
towards it.
The four largest orbiting bodies (gas giants) account for 99 % of the remaining
mass, with Jupiter and Saturn together accounting for more than 90 % of the mass.
The remaining objects of the Solar System, including the four terrestrial planets,
dwarf planets, satellites, asteroids and comets together make up less than 0.002 %
of the total mass of the Solar System.
Majority of the planets in the Solar System have their own secondary systems,
which orbit planetary objects, called natural satellites (or moons). In the case of
the four giant planets, there are also planetary rings – thin bands of tiny particles
Topic 2
22
that revolve around them. Most of the largest natural satellites synchronously rotate, with one side constantly facing their "parent".
Outside the Asteroid Belt, planets consist mainly of gases (such as hydrogen,
helium) and ice-like water, methane, ammonia, hydrogen sulfide and carbon dioxide. Objects located farther from the Sun mainly consist of materials with a lower
melting point. Icy substances make up most of the moons of the giant planets, as
well as most of Uranus and Neptune (that is why they are sometimes called “ice
giants”) and numerous small objects, lying beyond the orbit of Neptune. Together,
gases and ices are called volatile.
Formation and evolution:
The solar system formed 4.568 billion years ago from the gravitational collapse of a large molecular cloud consisting of hydrogen, helium and a small number of heavier elements fused by previous generations of stars (Pechernikova, Vityazev, 2012). When the region that would become the Solar System (known as the
pre-solar nebula) collapsed, conservation of angular momentum forced it to rotate
faster. The center, where most of the mass was collected, became hotter and hotter
than the surrounding disk. As the shrinking nebula spun faster and faster, it began
to flatten into a protoplanetary disk with a hot, dense protostar in the center. The
planets formed as a result of accretion from this disk, in which dust and gas were
attracted to each other and merged, forming ever larger bodies.
Earth in the Universe
Apart from being the birthplace and cradle of human civilization, Earth is the
only known planet in our Solar System capable of sustaining life. Earth is located
in the Inner Solar System between Venus and Mars, which, along with Mercury,
belong to the terrestrial planets. Earth has the most advantageous location from
the point of view of the habitable zone of our Sun (Ananyeva et al., 2020).
Earth has several names, including the “Blue Planet”, “Gaia”, “Terra” and “the
world”, which reflect its central role in the history of the creation of every human
culture that has ever existed. But the most unique and wonderful thing about our
planet is its diversity. There are not only an infinite number of plants, animals,
birds, insects and mammals, but they exist in any terrestrial environment.
Size, mass and orbit:
Having an average radius of 6371 km and a mass of 5.97×1024 kg, Earth is
the fifth largest and the fifth most massive planet in the Solar System. It is the
Earth in the Universe
23
largest planet of the Earth group, but it is smaller and less massive than any of the
gas/ice giants of the Outer Solar System. And with an average density of 5,514 g/cm3,
it is the densest planet in the Solar System (Milkov, 1990).
The Earth's orbit has a slight eccentricity (approximately 0.0167), the distance
from the Sun ranges from 147,095,000 km (0.983 au) at perihelion to 151,930,000 km
(1.015 au) at aphelion. The average distance is 149,598,261 km, which is one astronomical unit (AE) (Milkov, 1990).
The Earth's orbital period is 365.25 days, which is equivalent to 1.000017 Julian years. This means that every four years (in the so-called Leap Year) the Earth
calendar must include an additional day. Although technically a full day is considered as 24 hours, our planet takes exactly 23 hours, 56 minutes and 4 seconds to
complete one stellar revolution (0.997 Earth days).
If you look from the celestial North Pole, the movement of Earth and its axial
rotation occurs counterclockwise. From an observation point above the North
Poles of the Sun and Earth, Earth rotates around the Sun counterclockwise. The
Earth's axis is tilted by 23.439281° from the perpendicular of its orbital plane,
which affects seasonal fluctuations on the planet's surface with a period of one
tropical year (365.24 solar days) (Bobkov, 2012). In addition to temperature
changes, this also leads to the changes in the amount of sunlight received by the
hemisphere throughout the year.
Basically, when the North Pole is directed towards the Sun, it is the summer season in the Northern Hemisphere, and the winter season is in the Southern Hemisphere. In summer, the day lasts longer and the Sun rises higher in
the sky; while in winter the weather usually gets cooler, the days are shorter
and the Sun rises lower in the sky. There is a special phenomenon beyond the
Arctic Circle i.e. a lack of illumination, when there is no daylight at all for
part of the year up to six months at the North Pole, this time is known as "polar
night". In the Southern Hemisphere, the situation is exactly the opposite: at
the South Pole there is a "midnight sun" – the so-called polar day, that is, the
day lasts 24 hours.
Progress check test
1. What is the name of the galaxy in which our Solar system is located?
a. Andromeda
c. Milky Way
b. Large Magellanic Cloud
d. Alpha Centauri
Topic 2
24
2. How old is the Solar system?
a. 4.57 billion years
c. 3.8 billion years
b. 7.23 billion years
d. 11 billion years
3. During what period does Earth make one revolution around the Sun?
a. 120 days
c. 365 days 6 h 9 min
b. 90 days
d. 30 days
4. The seasons change on Earth due to:
a. the rotation of the Earth around its axis
b. the rotation of the Earth around the Sun
c. The rotation of the Earth around the Sun and the constant inclination to the
plane of the orbit
d. the attraction of the Moon
Project tasks
1. Compare the planets of the Earth group and the giant planets. What other
names do they have? What similarities and differences do these planets have?
2. Describe the movement of Earth around the Sun, and in the space of the
Universe.
3. What is unique about the Solar System – single out a few of its features.
25
T O PI C 3
Th e Ea r th’ s cr u st a n d t he s urf a c e o f E a rth
The shape of Earth resembles the shape of an oblate spheroid, a sphere flattened along the axis from pole to pole so that there is a bulge around the equator.
This bulge is the result of the rotation of Earth and the fact is that the diameter at
the equator is 43 kilometers larger than the diameter from pole to pole.
The internal structure of Earth, like that of other terrestrial planets, is distinguished by a metallic core, a mantle consisting of rocks and silicate minerals.
However, unlike other terrestrial planets, it has a distinct inner core of solid material and a liquid outer core. This inner core has an estimated radius of 1,220 km,
while the outer core extends beyond it by a radius of about 3,400 km.
The mantle and the earth's crust extend above the core. The Earth's mantle
extends to a depth of 2,890 km, making it the thickest layer of Earth. This layer
consists of silicate rocks rich in iron and magnesium, regarding the overlying crust
(Karlovich, 2013). Despite the fact that the mantle is made of solid matter, the high
temperatures inside the mantle make the silicate material plastic enough to be able
to flow for a very long time.
The upper mantle layer is made up of the lithospheric mantle (lithosphere) and
the asthenosphere. The first one consists of the crust and the cold, hard upper part of
the upper mantle (which tectonic plates consist of), while the asthenosphere is a relatively low–viscosity layer through which the lithosphere moves (Karlovich, 2013).
Mechanically the rigid lithosphere is divided into parts called tectonic plates.
These plates are rigid segments that move relative to each other on one of three
types of plate boundaries. These are known as convergent boundaries, in which
two plates converge together; divergent boundaries, in which two plates diverge;
and transformational boundaries, in which plates slide past each other.
The interaction between these plates is the cause for earthquakes, volcanic activity to take place (for example, the Pacific Ring of Fire), for mountains and oceanic deep-sea troughs to form. As tectonic plates move across the planet, the ocean
floor “is subducted under the leading edges of the plates at converging boundaries.
At the same time, upwelling of mantle material at divergent boundaries creates
mid-oceanic ridges. The combination of these processes constantly remakes oceanic crust back into the mantle.
Topic 3
26
Seven major plates are known as the Pacific, North American, Eurasian, African, Antarctic, Indo-Australian and South American, and some others include the
Arabian Plate, the Caribbean Plate, and the Nazca plate off the west coast of South
America and the Scottish Plate in the South Atlantic Ocean” (Milkov, 1990).
The Earth's surface features:
Unlike other planets in our Solar system, most of the Earth's surface is covered
with liquid water. In fact, about 70.8 % of the surface, which is 361.132 million km2,
is covered with water, with most of the continental shelf located below sea level.
The remaining 148.94 million km2 are above sea level (Milkov, 1990).
Whether underwater or above sea level, the terrain of Earth varies greatly from
place to place. The underwater surface has mountain ranges, as well as underwater
volcanoes, oceanic depressions, underwater canyons, oceanic plateaus and abyssal
plains. The remaining parts of the surface are mountains, plains, depressions, plateaus and other landforms.
Over long periods known as geological epochs, the surface undergoes some
changes due to tectonic activity and erosion which combined. Those irregularities
that are created or changed by plate tectonics are subject to constant weathering
and erosion that occur as a result of precipitation, flowing water, thermal cycles
and chemical influences. Glaciation, coastal erosion, coral reef formation and
large meteorite impacts also affect landscape changes.
The continental crust consists of three types of rocks with different densities:
igneous rocks, sedimentary rocks and metaphorical rocks. Igneous rocks can be
subdivided into granites and andesites (which are the most common) and basalt,
a denser form of volcanic rock that is less common on the surface but makes up
most of the ocean floor.
Sedimentary rocks, which make up 75 % of the continental surface (although
only 5 % of the earth's crust), are formed during the burial and compaction of
accumulated sediments. Metamorphic rocks are formed when sedimentary rocks
undergo transformation under the influence of heat and pressure and then form
materials such as gneiss, slate, marble, quartzite, etc.
The height of the earth's surface ranges from the lowest point: 418 m (on the
Dead Sea) to the estimated maximum height of 8848 m at the summit of Mount
Everest. The average height of the land above sea level is 840 m (Milkov, 1990). The
planet is divided into the Northern and Southern Hemispheres, and an arbitrary
The Earth's crust and the surface of Earth
27
division into the Eastern and Western Hemispheres is also recognized. The
Earth's land is divided into six continents: Africa, Eurasia, Australia, North and
South America and Antarctica.
The outermost layer of the earth's surface (known as the pedosphere) is soil,
which is a combination of minerals and organic compounds. This layer exists as
the interface between the lithosphere, atmosphere, hydrosphere and biosphere.
The total area of arable land is approximately 13,31 % of the Earth's surface,
with 4,71 % being permanent crops. About 40 % of the Earth's land is used for
arable land and pastures, or, according to estimates, 1,3×107 km2 is used for arable
land and 3,4×107 km2 is used for pastures.
Do a practical task:
Create a hypsometric profile of the ocean floor along one of the specified
parallels.
Project tasks
1. Explain how the continental type of the earth's crust differs from the
oceanic one.
2. What are lithospheric plates, what impact do they have on the earth's crust.
3. Describe the structure of Earth. Which layer is the most powerful? What
effect does it have on the surface of Earth?
28
T O P I C 4
Th e Ea r th’ s atm o sph e re.
Th e st r u ctu r e a n d c o mpo s iti o n of the tro p os phe r e .
Th e cl i mate of Ear t h
The Earth's air envelope is the atmosphere, which is heterogeneous and
also consists of several spheres (Table 1). The mass of the Earth's atmosphere is approximately 5.15×1021 g. The average air pressure at sea level is po =
= 1.0132 bar = 1013.2 mb (760 mm Hg), and the density is p = 1.27×10-3 g/cm3
(Mazurov, 2019). With altitude, air pressure and density decrease rapidly exponentially.
The structure of the atmosphere.
The total mass of the atmosphere is about a million times less than the mass of
the Globe itself.
Table 1
The structure of the atmosphere (according to Milkov, 1990)
Structural
part
Height
Temperature
Characteristics
The troposphere
0–12 (17) km
Falls by 6.5 °C for each km.
At the upper boundary, the
average t is -70 °C at the
equator, above the north pole 65 °C in winter, -45 °C in
summer
The troposphere is heated by
infrared radiation of the
Earth's surface. The bulk of
the air and almost all of the
water vapor is concentrated
The Earth’s atmosphere. The structure and composition of the troposphere. The climate …
29
End of the table 1
Structural
part
Height
Temperature
Characteristics
The s
tratosphere
12–25
km
-50 °C at the bottom
Isothermal layer below. Temperature rises at the upper
boundary
25–50 (55) km
At an altitude of 50 km about
0 °C. Ozone absorbs ultraviolet radiation in the region
(200–300 nm), protecting life
on the Earth's surface
The temperature increases due
to the decomposition reaction
of ozone, which is accompanied by the release of heat
The m
esosphere
up to 85
–95 km
Drops to -90 °C at the upper
boundary
The air pressure at the upper
boundary is about 200 times
less than at the Earth's surface
(99,5 % of the total mass of
the atmosphere is at a level up
to 80 km from the Earth's surface)
The t
hermosphere
(ionosphere)
85–800 km
Temperature increases with
altitude. During the day, at an
altitude of 800 km about 1500
°C
Ultraviolet and X-ray radiation
from the Sun ionizes air molecules. Therefore, the thermosphere is called the ionosphere. Radio waves are reflected from the ionosphere.
Hydrogen and helium become
predominant. The electrical
conductivity of the air increases sharply. The aurora
borealis
The e
xosphere
Over 800 km
Molecules move at tremendous speeds, sometimes flying into interplanetary space
Topic 4
30
The composition of the troposphere.
By composition, the air near the earth's surface contains 78 % nitrogen (N2)
and about 21 % oxygen (O2), i.e. these two elements account for about 99 % of
the air volume. A significant share belongs to argon (Ag) – 0,9 %. Important components of the atmosphere are ozone (O3), carbon dioxide (CO2), and water vapor
(Table 2).
Table 2
Composition of the air troposphere (according to Milkov, 1990)
Gas
Content, by volume, %
Content, by weight, %
Nitrogen (N2)
78,084
75,50
Oxygen (O2)
20,946
23,10
Argon (Ar)
0,932
1,286
Water (H2O)
0,5–4
-
Carbon dioxide (CO2)
0,032
0,046
Neon (Ne)
1,818×10−3
1,3×10−3
Helium (He)
4,6×10−4
7,2×10−5
Метан (CH4)
1,7×10−4
-
Krypton (Kr)
1,14×10−4
2,9×10−4
Hydrogen (H)
5×10−5
7,6×10−5
Xenon (Xe)
8,7×10−6
-
Nitrous oxide (N2O)
5×10−5
7,7×10−5
“Nitrogen is the most common gas in the troposphere, it is chemically inactive.
It plays a huge role in the vital activity of organisms, being an integral part of
proteins, however, it is absorbed not directly from the air, but through nitrogenfixing bacteria and algae” (Milkov, 1990).
Oxygen, on the contrary, is a very active element, the main specific function
includes the oxidation of organic matter, rocks and under-oxidized gases emitted
by volcanoes into the atmosphere. In an oxygen-free environment, the decomposition of organic matter would not occur. Oxygen reserves in the atmosphere are
replenished through photosynthesis, the time of one revolution of the mass of oxygen in the atmosphere is estimated at 4500–6000 years.
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