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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

how to calculate net electric field at a point
Bazel Reply
what are controlled variables
Link Reply
Independent variables in an experiment which influence the outcome results
Boss
Such as temperature when dealing with ohms law
Boss
variables whose amount is determined by the person doing the experiment
Clemencia
how to calculate exodation number
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Calculate relative atomic mass
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what is chemical bonding?
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Chemical Bonding is a mutual attraction between two atoms resulting from the simultaneous attraction between their nuclei and the outer elections
Sydney
How would you go about finding the resistance of an unknown resistor using only power supply, a voltmeter and a known resistance
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who is the scientist who discovered electromagnetism
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what happens to the galvanometer when the switch is closed ?
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hey
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Formula for concentration
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c=m/MV
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if given number of moles and volume , can use c=n/V
sibahle
Chemistry term three topic is stressing me out, I really need a huge help
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on what
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during a snooker competition ,a 200g ball A m moving with velocity va collide head on with a identical ball B that was at rest.A after the collision ball A remains at rest wile ball B moves on with a velocity of 4m/s? With what speed was ball a moving before the collision
mathew Reply
a vector can be resolved into a horizontal component only
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how to calculate normal force
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how to calculate wavelength
Lizoh
Hello. How does a real gas behave under low temperature and high pressure?
Valerie Reply
does a vector quantity include force and distance?
Lebo Reply
yes
Itumeleng
what's the difference between a vector and a scalar?
Keaobaka
vector is the physical quantity with magnitude and direction Scalar is the Physical quantity with magnitude only
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Newton's second law of motion
Thelma Reply
Newton second law motin
Shife
Newton's second law of motion: When a resultant/net force acts on an object, the object will accelerate in the direction of the force at an acceleration directly proportional to the force and inversely proportional to the mass of the object.
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newtons third law of motion
Ayakha
when object A exert a force on object B object B SIMULTANEOUS exert a force of equal magnitude on object A
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what is tail to tail method
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it is a method used tobrepresent vectors it is a rectangle
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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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