48
ENVIRONMENT, POLLUTION, DEVELOPMENT: THE CASE OF UZBEKISTAN
photochemical reactions in the stratosphere – first of all, the formation
and disintegration
of ozone molecules, and also the intensive sorption
of ultraviolet light.
The concentration of gases that form the upper layers of the
atmo sphere is considerably lower. These
gases are in an ionised
state, and they are subject to the influence of high-energy electro-
magnetic radiation coming from the Sun and outer space. Therefore,
molecules move at much higher speeds in the rarefied air of the
upper atmo sphere. Reactions taking place in these parts of the atmo-
sphere are rather different from those near the Earth’s surface.
The hydrosphere
is the whole of all water on the Earth’s surface
and in the Earth’s crust near the surface.
The World Ocean comprises
the largest part of it. The cycling of substances is mostly associated
with the Earth’s hydrological cycle. The presence of water is a
precondition
for life on the Earth, and the existing forms of living
organisms are to a great extent determined by water. Moreover,
water is the main substance forming living organisms. Water is not
only the main component of the hydrosphere; it also significantly
affects the processes in the biosphere, atmo sphere and – being a
critical factor for many geological processes – the litho sphere. The
role of water in the environ ment is decisive
not only due to its total
volume on the Earth but also due to its substantial properties.
The mass of the hydrosphere is 1.5 × 10
18
tons, and its total
area (ocean + glaciers and ice caps + lakes + rivers + swamps +
wetlands) is 383 million square kilometres, which is 75% of the total
area of the Earth’s surface (510 million square kilometres).
Asthenosphere
Transition zone or
the
middle layer of the mantle
Lower mantle
Transition or ‘D’ layer
Outer core
Inner core
Continental crust
(20–60 km)
Seawater
(0–5 km)
Oceanic crust
(5 km)
Upper mantle
400 km
670 km
2900 km
5100 km
6378 km
Lithosphere
(50–200km)
Figure 4.4.
Inner
structure of the Earth
4. HUMANS AND THE ENVIRONMENT
49
The hard and rigid outer layer of the Earth – the litho sphere –
is up to 200 km deep, and it comprises the Earth’s crust and the
outer part of the upper mantle. The litho sphere is underlain by
the astheno sphere and the deeper part
of the upper mantle made
of magma that can come to the Earth’s surface during volcanic
eruptions. The Earth’s outer core is liquid, and it makes up ~30%
of the Earth’s mass, whereas the inner core is solid and composed
mostly of iron and nickel (Figure 4.4).
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