Page 67 - Journeys Through Society-7

Hydrosphere
Four realms of the Earth
important constituent of the atmosphere which
condenses to cause precipitation.
Wow Fact
Ozone gas protects us from the harmful
ultraviolet rays of the Sun.
The Earth’s atmosphere is divided into various layers,
which are described as follows.
Troposphere: It is the bottommost layer of the
atmosphere and is the most important because all
weather activities occur here. This layer also contains
all the life-sustaining gases. Can you name them?
Stratosphere: It lies just above the troposphere and
contains the ozone layer. Find out the importance of
this layer.
Mesosphere: It is the next layer. This layer contains
electrically charged particles known as ions which
help in radio communication between distant places
on the Earth.
Thermosphere: It extends up to a height of 400 km.
This layer is characterised by a rapid rise in
temperature with increasing altitude.
Exosphere: It is the outermost layer and it merges into
space.
When atmospheric conditions, which include winds,
temperature, humidity, precipitation and
atmospheric pressure, change, they cause changes in
the weather and climate.
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Hydrosphere is made up of all the water bodies on the
Earth. The frozen ice in the glaciers and polar ice caps,
groundwater and the water vapour in the air also
constitute the hydrosphere. Oceans, that make up 71
per cent of the Earth's surface, form the major part of
the hydrosphere.
Water is circulated in all realms of the Earth through
the water cycle which supports life on the planet.
Oceans are a great source of food and mineral wealth.
Oceans are not only important for trade and
transportation but also help in moderating the climate
of coastal areas.
Lithosphere
Lithosphere comprises the solid outer crust of the
Earth. It is made up of rocks. This crust consists of the
continents and the ocean beds. The various landforms
include mountains, plateaus, plains, valleys, hills,
deltas, islands, peninsulas, etc.
The lithosphere is the home to humans and many
plants and animals. Can you say why?
Biosphere
Biosphere is the narrow zone of contact between air,
water and land, where living organisms exist. It makes
the Earth a unique planet. It is made up of distinctive
zones called 'biomes' or 'ecosystems' which coincide
with the climatic zones of the world. An ecosystem
includes all the living things (plants, animals and
organisms) in a given area, interacting with each other,
and also with their physical environments.
Wow Fact
The biosphere has been in existence for
about 3.5 billion years. The biosphere’s
earliest life-forms, called prokaryotes,
survived without oxygen.
Ecosystems found on land are called terrestrial
ecosystems, while those found in water are called
aquatic ecosystems. Marine ecosystems exist only in
oceans and seas.
Ecosystems are subject to change due to several
factors. These changes affect the plant and animal life
existing in that environment.