Talks about a summarized view of the atmosphere. the composition, structure and what it really entails

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UNIVERSITY OF CAPE COAST
COLLEGE OF HUMANITIES AND LEGAL STUDIES
FACULTY OF SOCIAL SCIENCES
DEPARTMENT OF GEOGRAPHY AND REGIONAL PLANNING
ADDAI JULIUS PAMFO
SS/GRP/18/0003
BSc GEOGRAPHY AND REGIONAL PLANNING
GEO 101 INTRODUCTION TO PHYSICAL GEOGRAPHY (GROUP 3)
QUESTION: Give an account of the structure and composition of the atmosphere
explaining five (5) of its importance to the life of humans?

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The atmosphere of the earth first of all is the layer of gases which is commonly known
as air, which surrounds the planet earth and is restrained by earth’s gravity. The atmosphere
of the earth contains gases that help it maintain its shape, structure and relevance. They are
grouped into about for categories, which are; the major gases, trace gases, aerosols and
pollutants.
The major gases are; Nitrogen (N2) which is largely an inert gas and constitutes about
78% of the earth’s atmosphere. There is Oxygen (O2) which is required for the respiration of
all animal lives on earth and is 21% in the atmosphere. Argon (Ar) also is a major gas which
is very inert noble gas, meaning, it does not take part in any chemical reaction under normal
circumstances, and its only 0.93% in the atmosphere. The atmospheric pressure at sea level is
1.013 bar (b) / 1013milibars (mb) / 1 atmospheres (atm) / 760 millimeters of mercury Hg
(mmHg) / 760 Torr / 14.6959 pound per square inch (psi) / 101325 pascals. The total
atmospheric mass is 5.1480 x 1018 kilograms (kg) / 1.135 x 1019pounds (lb.). The mass of
earth’s atmosphere is distributed approximately as follows; 50% is below 5.6km, 90% is
below 16km and 99.99997% is below 100km, the Karman line. The density of air at sea level
is about 1.2kg/m3 (1.2g/L; 0.0012 g/cm3).
The important trace gases are Carbon Dioxide (CO2) which is only about 0.0325%
component of the atmosphere. It is required by plants for photosynthesis is and also one of a
class called greenhouse gases (keeps the earth warm). Water vapor (H2O) is also in a
component in the atmosphere, while it is nearly absent in most part of the atmosphere, its
concentration can range to up to 4% in very warm, humid areas close to the surface. It range
from 0.001% - 5% in the atmosphere. Ozone (O3) is almost all found in the layer about 9-
36miles (15-60kilometres) in altitude. The ozone gas is very irritating to people’s body but
absorbs high Ultraviolet (UV) radiation from the sun which is very harmful to humans also.

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The ozone layer if it were all to be transported to the surface of the surface of the earth, the
ozone gas would form a layer about 0.1-0.16inches (2.5-4.0millimeters) thick.
Aerosols also are widely variety of tiny particles suspended in the air. Examples are; bits of
suspended soil, desert sand, tiny smoke particles from a forest fire, salt particles left over
after a droplet of ocean water has evaporated, plant pollen, volcanic dust plumes and particles
formed from the pollution created by a coal burning power plant.
Pollutants also are gases in the atmosphere but they rather threatens and endangers human
health. They are; Carbon Monoxide (CO) which is primarily produced by incomplete
combustion of fuel. Sulphur Dioxide (SO2) which is from coal emission from electricity
generation and industry and can form acid precipitation also. Nitrogen Dioxide (NO2) which
is highly reactive, and has a foul smell. Tropospheric Ozone (O3) is from interacting sunlight,
heat, nitrogen oxides and volatile carbons and is a major component of smog. Lead is also a
pollutant which is added to gas and used in industrial metal smelting and it bio-accumulates
and causes nervous system malfunctioning.
The atmosphere is in structures or layers of which each of them is distinct from the
other in terms of temperature, altitude, gas compositions, functions and others.
The lowest atmosphere is called the troposphere, and it is where all weather occurs; clouds
form and precipitation falls, wind blows, humidity varies from place to place, and atmosphere
interact with the surface below. Within the troposphere, the temperature decrease with
altitude at a rate of about 6.5ºC per km. it is the closest layer of the atmosphere to the earth
extending up to about 10 – 18km above earth’s surface. It contains 75 – 80% of earth’s
atmospheric mass. It is wider at the equator than at the poles. Temperature and pressure falls
as you go up. At the very top of the troposphere is the tropopause where temperature reaches
a (stable) minimum. Some scientists call the tropopause a “thermal layer” or “cold trap”

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At the uppermost boundary of the tropopause, air temperature reaches about -100ºC and then
begins to increase with altitude. This layer is of increasing temperature is called the
stratosphere. The cause of the temperature reversal is as a result of a layer of concentrated
ozone. Ozone and Oxygen gas both absorb short wave solar radiation. In the series of
reaction that follows, heat is reflected. This heat the atmosphere in the layer about 20 – 45km
and gives the stratosphere its characteristic temperature increase with altitude. It is very
important to recognize the difference between the ozone layer in the stratosphere and the
ozone present in trace amounts in the troposphere. Stratospheric ozone is produced when
energy from the sun breaks apart Oxygen (O2) gas molecules into Oxygen (O) atoms, these O
atoms then bond with other O2 molecules to form Ozone (O3). Tropospheric Ozone on the
other hand is a pollutant produced when emission from fossil fuel burning interact with
sunlight. These have been found in very thin widespread clouds in the polar stratosphere
under extremely cold conditions. These clouds called Polar Stratospheric Clouds (PSCs)
appear to be crystals of ice and nitric acid and they play a key role in the development of the
Ozone Hole. It extends from the troposphere to about 50km above ground. At the edge of it is
the stratopause which serves as a boundary between the stratosphere and the mesosphere
Above the stratosphere, temperature begins to drop again in the next layer of the atmosphere
called the mesosphere. This temperature decrease results from the rapidly decreasing density
of the air of at that altitude. It extends from the stratopause at an altitude of about 50km to the
mesopause at 80 – 85km above sea level. The atmosphere here is very rarefied nevertheless
thick enough to slow down meteors hurtling into the atmosphere where they burn up, leaving
fiery trails in the night sky. Its temperature reaches a minimum of about -90ºC at the
mesopause. The air here is far too thin to breath, and the pressure at the bottom of this layer is
well below 1% of the pressure at sea level, and continues dropping as you go higher.
Lightning induced discharges known as Transient Luminous Events (TLEs) occasionally

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form in the mesosphere above atmospheric thunderclouds. It is too high above the earth to be
accessed by jet-powered aircraft and balloons but can be mainly accessed by sounding
rockets and rocket-powered aircraft.
At the outer reaches of earth’s atmosphere, the intense unfiltered radiation from the sun
causes molecules like Oxygen (O2) and Nitrogen (N2) to break apart into ions. The release of
energy from these reactions actually causes the temperature to rise again in the thermosphere.
The thermosphere extends from the mesopause at an altitude of about 80 km up to the
thermopause at an altitude of about 500 – 1000km. Its height varies considerably due to the
changes in solar activity. The temperature in this layer ranges from 500ºC to 2000ºC. The
layer is completely cloudless and free of water vapor. However, non-hydro meteorological
phenomena such as the aurora borealis and aurora Australis are occasionally seen in the
thermosphere. The International Space Station orbits in this layer between 350 and 420km.
The thermosphere lies at the lower boundary of the exosphere called the exobase.
The exosphere is the outermost layer of earth’s atmosphere and extends from the exobase at
an altitude of about 700km above sea level to about 10,00km where it merges into the solar
wind. This layer is mainly composed of extremely low densities of helium, hydrogen and
several heavier molecules including nitrogen, oxygen and carbon dioxide closer to the
exobase. The air here is constant, though very gradually “leaking out of earth’s atmosphere
into outer space”. There is no clear-cut upper boundary where the exosphere finally fades
away into space. The latter value of its distance is about halfway to the moon.
The ionosphere is a sequence of the atmosphere that is ionized of solar radiation. It is
responsible for auroras and during daytime hours it stretches from 50 – 1000km and includes
the mesosphere, thermosphere and parts of the exosphere. Ionosphere forms the inner edge of
the magnetosphere. This is where high energy radiation from the sun has knocked electrons

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loose from their parent atoms and molecules to form ions. The ionosphere reflects and absorb
radio waves allowing us to receive shortwave radio broadcasts in the New Zealand from other
parts of the world. This region is what makes radio communication possible.
The magnetosphere is the outer region surrounding the earth, where charged particles spiral
along the magnetic field lines. It traps electrons and protons concentrating them in two bands
about 3000 and 16000km above the globe; the Van Allen radiation belts.
The homosphere and heterosphere also are defined by whether the atmosphere gases are well
mixed. The homosphere includes the troposphere, stratosphere, mesosphere and the lowest
parts of the thermosphere. The heterosphere includes the exosphere and most of the
thermosphere.
The planetary boundary layer is the part of the troposphere that is closest to the earth’s
surface and is directly affected by it, mainly through turbulent diffusion.
The earth’s atmosphere is very important in many ways. Without the protective layer of
gases that make up the atmosphere, the harsh conditions of the solar system would render the
planet barren and lifeless like the moon.
The atmosphere helps to maintain the earth’s temperature. Venus has a very thick atmosphere
which traps most of the suns energy making its surface temperature to be about 463ºC
(864ºF) and Mars also has a very thin atmosphere making its surface temperature to be about
-63ºC (-80ºF). Looking also at the moon which has no protective atmosphere, temperatures
can range from 121ºC in the sun to -157ºC in the shade, nevertheless, on earth, ,molecules in
the atmosphere absorb the sun’s energy as it arrives, spreading that warmth across the planet.
The molecules also trap reflected energy from the surface, preventing the night side of the
earth from being too cold. Without the atmosphere, it will get really hot in the daytime and
extremely cold at night.

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The atmosphere also serves as protective shield against radiation and cosmic rays. The sun
bombards and inflicts upon the solar system with Ultraviolet (UV) radiation, and without
protection, that radiation can cause severe damage to skin and eyes. The ozone layer in the
atmosphere blocks much of the radiation from reaching the surface. Dense layers of
molecular gases also absorb cosmic rays, gamma rays and X rays, preventing these energetic
particles from striking living things and causing mutations, flora, fauna and other genetic
damage. The ultraviolet radiation can destroy living cells causing harm to our skin and
leading to skin cancer. The solar radiations are located in the ultraviolet region (frequency
from 100 – 400nm).
The atmosphere also serves as physical protection to the earth. The solar system may seem
like a vast and empty place, but in reality, it is full of debris and small particles of leftovers
from planetary creation or collision in the asteroid belt. According to NASA, more than
100tons of space debris strikes earth every single day, mostly in the form of dust and tiny
particles. When they encounter the molecules that make up the earth’s atmosphere, however,
the resulting friction destroys them long before they reach the ground. Without physical
protection from the atmosphere, the surface of the earth would resemble that of the moon,
pockmarked with impact craters.
The atmosphere also is important because it contains oxygen and carbon dioxide, which we
and other living organisms either breathe or use for photosynthesis. Through the
photosynthesis, oxygen is excreted which also helps in respiration. Then the cycle continues,
and by this, living organisms gain life to exist. It gives plants also sunshine for
photosynthesis. Without the atmosphere, the earth would not have been able to support life.
The atmosphere again serves an important purpose as a medium for the movement of water.
Water evaporates out of oceans and turns to vapor, condenses as it cools and falls as rain,

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providing life-giving moisture to otherwise dry areas of the continents. According to the U.S.
Geological Survey, the earth’s atmosphere holds around 12900cubic kilometers worth of
water at any given time. Without an atmosphere, it would simply boil away into space or
remain frozen in pockets below the surface of the planet.
So therefore, looking at the structure, composition and the usefulness of the earth’s
atmosphere, there is no doubt that it is the most complex, perfectly organized structure in the
universe and we have to treat it well if we only want to maintain its usefulness in
organization, mostly by limiting the out flux of Chlorofluorocarbons (CFCs) into our
atmosphere, which depletes the ozone layer in particular. Thank You.
REFERENCE
1. Available at; https://www.encyclopedia.com/science
2. Available at; science.jrank.org
3. Available at; elte.prompt.hu
4. Available at; https://climate.ncsu.edu
5. Available at; https://www.ess.uci.edu
6. Available at; https://en.wikipedia.org
7. Available at; www.geol-amu.org
8. Available at; www.chem1.com
9. Available at; http://www.geographynotes.com

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