General Knowledge for SSC Exams (Atmosphere)
The Earth’s atmosphere is a thin layer of gases that
surrounds the Earth. It composed of 78% nitrogen, 21% oxygen, 0.9% argon, 0.03%
carbon dioxide, and trace amounts of other gases. This thin gaseous layer
insulates the Earth from extreme temperature; it keeps heat inside the
atmosphere and it also blocks the Earth from much of the Sun’s incoming
The Earth’s atmosphere is about 300 miles (480 km) thick, but
most of the atmosphere (about 80%) is within, 10 miles (16 km) of the surface of
the Earth. There is no exact place where the atmosphere ends; it just gets
thinner and thinner, until it merges with outer space.
At sea level, the air pressure is about 14.7 pound per square
inch. As your altitude increases for example, if you climb a mountain, the air
pressure decreases. At an altitude of 10,000 feet, the air pressure is 10 pound
per square inch (and there is less oxygen to breathe).
The Layers of the Atmosphere
Thermosphere: The thermosphere is a thermal
classification of the atmosphere. In the thermosphere, temperature increases
with altitude. The thermosphere includes the exosphere and part of the
Ionosphere: The ionosphere starts at about 43-50 miles
(70-80 km) high and continues for hundreds of miles (about 400 miles = 640 km).
It contains many ions and free electrons (plasma). The ions are created when
sunlight hits atoms and tears off some electrons. Auroras occur in the
Exosphere: The exosphere is the outermost layer of the
Earth’s atmos-phere. The exosphere goes from about 400 miles (640 km) high to
about 800 miles (1,280 km). The lower boundary of the exosphere is called the
critical level of escape, where atmospheric pressure is very low (the gas atoms
are very widely spaced) and the temperature is very low.
Mesosphere: The mesosphere is charact-erized by temperature
that quickly decrease as height increases. The mesosphere extends from 31 to 50
miles (17 to 80 kilometer) above the earth’s surface.
Stratosphere: The stratosphere is characterized by a
slight temperature increase with altitude and the absence of clouds. The
stratosphere extends between 11 and 31 miles (17 to 50 kilometer) above the
earth’s surface. The earth’s ozone layer is located in the stratosphere. Ozone,
a form of oxygen, is crucial to our survival; this layer absorbs a lot of
ultraviolet solar energy. Only the highest clouds (cirrus, cirrostratus, and
cirrocumulus) are in the lower stratosphere. Tropopause: The tropopause is the
boundary zone (or transition layer) between the troposphere and the
stratosphere. The tropopause is characterized by little or no change in
temperature altitude increases.
Troposphere : The troposphere is the lowest region in
the Earth’s (or any planet’s) atmosphere. On the Earth, it goes from ground (or
water) level up to about 11 miles (17 kilometer) high. The weather and clouds
occur in the troposphere. In the troposphere, the temperature generally
decreases as altitude increases.
Formation of the Atmosphres
The Lath atmosphere was formed by planetary degassing, a
process in which gases like carbon dioxide, water vapor, sulphur dioxide and
nitrogen were released from the interior of the Earth from volcanoes and other
processes. Life forms on Earth have modified the composition of the atmosphere
since their evolution.