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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

An unknown gas has pressure,volume and temprature of 0.9atm,and 120°C.how many moles of gas are present?
Chrislyn Reply
Can you, if possible send me more quizzes
Bradley Reply
What is selmon
heath Reply
how long it takes for 25ml ethanol to be evaporated?
Kgaugelo Reply
how to calculate acceleration
Sphe Reply
It depends
Mbongeni
Please state the Newton third low
Malwandla
hy
Nelito
Newton's Third law states that to every force applied, there's an equal but opposite reaction
Lala
difference between a head and tail methods
Zenande Reply
difference between a head-to-tail and tail-to-tail
Zenande
head to tail you draw each vector starting head of the previous vector and tail to tail you construct a parallelogram whereas you started the two vectors from the same axis(from their tails)and the diagonal between the vectors is the resultant vector,tail to tail only includes two vectors
Mbongeni
what is a normal force
Zenande Reply
a normal force is the force that the surface applies on the object. The force is perpendicular to the surface.
Minaa
Lewis structure for C2H2
Mthokozisi Reply
H-C-H
Koketso
what is the mathematical relationship between velocity and time?
Oyisa Reply
How do we find a resulted force of a vector
Dann-boy Reply
what is the formula for calculating tension
Kagiso Reply
You can use simultaneous equations or T=mg+ma
sibahle
- Which formula can you use if you want to calculate acceleration?
Pretty
to calculate acceleration you use formula Vf -Vi divided by the time (t)
sholan
What is the formula of calculating tension
sibahle Reply
I don't think there's a formula u just have to use all information in that type of situation
Gwebzi
can a mixture of atoms make a molecule
Keamogetse Reply
yes
Wandile
What is the different between Valence and Valency?
Lil
define the term "resultant"
Austin Reply
the sum of all the forces acting on an object
Think
carring out an investigation of the relationship of acceleration and net force with mass kept constant
Ronald
Fnet=ma
Wandile
Hi
Lil
The definition of Newtons Law of Universal Gravitation
Lil
every particle in the universe attract every particle with a force that is directly proportional to the product of their masses but inversely proportional to the square of the distance between them.
Koketso
how to calculate coefficient of kinetic force
Bhereza Reply
kinetic friction × Normal force
Murunwa

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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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