46
ENVIRONMENT, POLLUTION, DEVELOPMENT: THE CASE OF UZBEKISTAN
equilibrium between the geochemical processes going on in the
organic nature and the activity of human beings. At the same time,
the atmo sphere in its present state is a result of long evolution.
After the Earth had been formed, the early atmo sphere was
composed
of methane, ammonia, water vapour and hydrogen. This
atmo sphere did not shield the Earth even from short-wavelength
electro magnetic radiation from outer space, and it was chemically
reductive. Therefore, the first living organisms evolved in water,
which protected them from the electro magnetic radiation of short
wavelength and precluded the breakdown of organic substances
(especially DNA and proteins). The development of photosynthetic
organisms brought about further changes in the atmo sphere’s
composition. These organisms are capable of absorbing carbon
dioxide and water, producing carbohydrates and oxygen. Increasing
concentration of oxygen in the atmo sphere created the Earth’s ozone
layer, and the composition of the atmo sphere became very much like
it is today. During the atmo sphere’s evolution, the concentration of
hydrogen decreased as it was bound up
into chemical compounds
as well as diffused into outer space. Hence, photosynthesis and the
development of living organisms can be deemed as the combination
of factors crucial for the formation of an oxygen-rich atmo sphere as
we know it today.
The specific properties of the atmo sphere that significantly
affect the processes on the Earth are its mobility and reactivity.
The atmo sphere can be regarded as a barrier that protects the life
processes on the Earth, as far as it absorbs charged particles and a
large part of high-energy electro magnetic radiation from the Sun,
which would otherwise cause damage and destruction of living
organisms. Radiation with a longer wavelength and weaker energy
can reach the Earth’s surface, while short-wavelength radiation
(ultraviolet light, X-rays, γ-rays) is absorbed in the upper layers of the
atmo sphere. The atmo sphere has an indispensable role in balancing
the Earth’s temperature. The atmo sphere
contains carbon dioxide
and oxygen. Plants use the former for photosynthesis, while living
organisms use the latter for breathing. Furthermore, the atmo sphere
plays a vital role in the global cycling of substances (carbon, sulphur,
nitrogen, metals) and in the hydrological (water) cycle. In addition, a
considerable part of meteorite mass coming from outer space burns
out in the atmo sphere.
Temperature and the atmo sphere’s chemical composition can also
be quite different at different heights. The atmo sphere has a layered
structure; therefore, depending on the distance from the Earth’s
surface, many of its characteristics as well as composition are variable
(Figure 4.3). The upper layers of the atmo sphere have a considerably
different composition than the much denser lower layers, in which
Even if the atmosphere’s
mass is relatively small
(0.00009% of the Earth’s
mass, 0.044% of the
mass of the Earth’s crust,
0.6% of the hydrosphere’s
mass), its role is tremen‑
dous.
The atmospheric
gases are involved in
an active substance
exchange with the
lithosphere, biosphere
and hydrosphere, taking
active part in all kinds of
migration processes of
substances and elements.
The existence of the
atmosphere is the pre‑
condition of possibility
for life on the Earth, whe‑
reas
the life processes
themselves substantially
affect the atmosphere’s
composition. Human
activities cause changes
in all systems of the Earth,
and it is the atmosphere
which is affected most.
The atmosphere’s high
mobility also supports
transport of airborne pol‑
lutants from one area of
the Earth to other regions
and even their dispersion
on a global scale. To be
sure, a large part of the
processes taking place in
the biosphere depend on
the
composition of the
air that is used for ma‑
intaining life processes,
especially in the case of
much more complicated
organisms. Even
microscopic amounts
of toxic substances can
cause adverse effects on
human health if exposure
takes place for longer
periods of time.
4. HUMANS AND THE ENVIRONMENT
47
the main mass of the atmo sphere’s gases is concentrated (the air mass
within 30 km from the Earth’s surface makes 99% of the total mass
of the atmo sphere). The Earth’s atmo sphere is in a state of dynamic
equilibrium. The atmo spheric pressure changes evenly depending
on the distance from the Earth and other factors. However, the
temperature decreases within the tropo sphere, then it increases
again in the stratosphere due to the interaction of atmo spheric gasses
with solar radiation. High-energy electro magnetic
radiation from
outer space initiates ionisation in the upper layers of the atmo sphere,
splitting even stable molecules. Gas molecules reach high speeds as
a result of collisions with the quanta of electro magnetic radiation in
the rarefied air of the atmo sphere’s upper layers. At the same time,
these processes govern the sorption of electro magnetic radiation,
which is most intense at the top layers of the atmo sphere, although it
occurs, to a large extent, at lower layers as well.
Thermosphere
Mesosphere
Stratosphere
Troposphere
-100
-60
-20
20
60
40
0
-40
-80
0
20
40
60
80
100
120
Temperature (°C)
H
ei
gh
t (
km)
The layer closest to the Earth’s surface is called tropo sphere.
The tropo sphere’s height and processes taking place in it depend on
the Earth’s shape, movements of air masses as well as many other
factors, including the anthropogenic ones. Since water vapour
condensates at the upper
limit of the tropo sphere, it does not reach
the atmo sphere’s upper layers, where water molecules could be split
in photochemical reactions, and the resultant hydrogen – diffused
into outer space.
In the stratosphere, air temperature rises as the distance from
the Earth increases. The rise in temperature is a consequence of
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