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The atmosphere

Our earth is truly an amazing planet! Not only is it exactly the right distance from the sun to have temperatures that will support life, but it is also one of the only planets in our solar system to have liquid water on its surface. In addition, our earth has an atmosphere that has just the right composition to allow life to exist. The atmosphere is the layer of gases that surrounds the earth. We may not always be aware of them, but without these gases, life on earth would definitely not be possible. The atmosphere provides the gases that animals and plants need for respiration (breathing) and photosynthesis (the production of food), it helps to keep temperatures on earth constant and also protects us from the sun's harmful radiation.

In this chapter, we are going to take a closer look at the chemistry of the earth's atmosphere and at some of the human activities that threaten the delicate balance that exists in this part of our planet.

The composition of the atmosphere

Earth's atmosphere is made up of a mixture of gases. Two important gases are nitrogen and oxygen, which make up about 78.1% and 20.9% of the atmosphere respectively. A third gas, argon, contributes about 0.9%, and a number of other gases such as carbon dioxide, methane, water vapour, helium and ozone make up the remaining 0.1%. In an earlier chapter, we discussed the importance of nitrogen as a component of proteins, the building blocks of life. Similarly, oxygen is essential for life because it is the gas we need for respiration. We will discuss the importance of some of the other gases later in this chapter.

Interesting fact

The earth's early atmosphere was very different from what it is today. When the earth formed around 4.5 billion years ago, there was probably no atmosphere. Some scientists believe that the earliest atmosphere contained gases such as water vapour, carbon dioxide, nitrogen and sulfur which were released from inside the planet as a result of volcanic activity. Many scientists also believe that the first stage in the evolution of life, around 4 billion years ago, needed an oxygen-free environment. At a later stage, these primitive forms of plant life began to release small amounts of oxygen into the atmosphere as a product of photosynthesis. During photosynthesis, plants use carbon dioxide, water and sunlight to produce simple sugars. Oxygen is also released in the process.

6 C O 2 + 6 H 2 O + sunlight C 6 H 12 O 6 + 6 O 2

This build-up of oxygen in the atmosphere eventually led to the formation of the ozone layer, which helped to filter the sun's harmful UV radiation so that plants were able to flourish in different environments. As plants became more widespread and photosythesis increased, so did the production of oxygen. The increase in the amount of oxygen in the atmosphere allowed more forms of life to exist on Earth.

If you have ever had to climb to a very high altitude (altitude means the 'height' in the atmosphere), you will have noticed that it becomes very difficult to breathe, and many climbers suffer from 'altitude sickness' before they reach their destination. This is because the density of gases becomes less as you move higher in the atmosphere. It is gravity that holds the atmosphere close to the earth. As you move higher, this force weakens slightly and so the gas particles become more spread out. In effect, when you are at a high altitude, the gases in the atmosphere haven't changed, but there are fewer oxygen molecules in the same amount of air that you are able to breathe.

Questions & Answers

why don't we insert the negative sign for 5 × 10 - 9 when substituting
Mpho Reply
Why does an enclosed gas exert pressure on the walls of a container
Palesa Reply
State the gay lussacs law
Anna Reply
what is the coefficient of Na in order to balanced the equation?_Na + MgCl2=2NaCl+Mg?
Arcel Reply
the combining power of an element, especially as measured by the number of hydrogen atoms it can displace or combine with.
Dealon Reply
download periodic table from play Store...it will explain everything to u
what are orbitals
Sphe Reply
examples of atoms whose Valence energy levels are not full and more to bond and become more stable
What is a valency
what is vacuum
Njabulo Reply
Vacuum, space in which there is no matter or in which the pressure is so low that any particles in the space do not affect any processes being carried on there. It is a condition well below normal atmospheric pressure and is measured in units of pressure (the pascal).
evidence of reaction
Jason Reply
what is the variance if h²4h=5
Kabelo Reply
it's part of chemistry....u have to understand the difference between between hydrogen bonds and the strengthness
Pride Reply
I know the difference between hydrogen bonds and strengthness
the definition and the applications
Pride Reply
when a net force is applied on an object of mass ,it will accelerate in the direction of the net force . Acceleration is directly proportional to the net force and inversely proportional to the of an object
so what about intermolecular force
what kind of help u want
Pride Reply
about neuton's second law
I'm going to work with you guys
Pride Reply
what are vectors
Matlakala Reply
is the physical quantities that has both magnitude and direction
How is the magnitude calculated
Zinhle Reply
which chapter are u doing
snells law
forces calculating the magnitude of normal force

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Source:  OpenStax, Siyavula textbooks: grade 11 physical science. OpenStax CNX. Jul 29, 2011 Download for free at http://cnx.org/content/col11241/1.2
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