# Composition and structure  (Page 2/3)

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Earth's atmosphere

The Earth's atmosphere is a layer of gases that surround the planet, and which are held there by the Earth's gravity. The atmosphere contains roughly 78.1% nitrogen, 20.9% oxygen, 0.9% argon, 0.038% carbon dioxide, trace amounts of other gases, and a variable amount of water vapour. This mixture of gases is commonly known as air. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation and reducing temperature extremes between day and night.

## The structure of the atmosphere

The earth's atmosphere is divided into different layers, each with its own particular characteristics ( [link] ).

## The troposphere

The troposphere is the lowest level in the atmosphere, and it is the part in which we live. The troposphere varies in thickness, and extends from the ground to a height of about 7km at the poles and about 18km at the equator. An important characteristic of the troposphere is that its temperature decreases with an increase in altitude. In other words, as you climb higher, it will get colder. You will have noticed this if you have climbed a mountain, or if you have moved from a city at a high altitude to one which is lower; the average temperature is often lower where the altitude is higher. This is because the troposphere is heated from the 'bottom up'. In other words, places that are closer to the Earth's surface will be warmer than those at higher altitudes. The heating of the atmosphere will be discussed in more detail later in this chapter.

The word troposphere comes from the Greek tropos , meaning turning or mixing . The troposphere is the most turbulent (or agitated) part of the atmosphere and is the part where our weather takes place. Weather is the state of the air at a particular place and time e.g. if it is warm or cold, wet or dry, and how cloudy or windy it is. Generally, jet aircraft fly just above the troposphere to avoid all this turbulence.

## The stratosphere

Above the troposphere is another layer called the stratosphere , where most long distance aircraft fly. The stratosphere extends from altitudes of 10 to 50km. If you have ever been in an aeroplane and have looked out the window once you are well into the flight, you will have noticed that you are actually flying above the level of the clouds. As we have already mentioned, clouds and weather occur in the troposphere, whereas the stratosphere has very stable atmospheric conditions and very little turbulence. It is easy to understand why aircraft choose to fly here!

The stratosphere is different from the troposphere because its temperature increases as altitude increases. This is because the stratosphere absorbs solar radiation directly, meaning that the upper layers closer to the sun will be warmer. The upper layers of the stratosphere are also warmer because of the presence of the ozone layer . Ozone (O ${}_{3}$ ) is formed when solar radiation splits an oxygen molecule (O ${}_{2}$ ) into two atoms of oxygen. Each individual atom is then able to combine with an oxygen molecule to form ozone. The two reactions are shown below:

explain why HCL is a Bronstead lowry acid . use an equation of HCL in water to explain
what is electron. ( you should not allowed to tell it properties in it defination.)
a charged particle.
Siyabonga
investigative question
how do you create a bomb
how can I create a bomb
Nasty
how can I create a bomb
Nasty
how can I create a bomb
Nasty
how can I create a bomb
Nasty
how can I create a bomb
Nasty
how can I create a bomb
Nasty
how can I create a bomb
Nasty
how can I create a bomb
Nasty
how can I create a bomb
Nasty
if you want to create bomb use this chemical substance oxidised, sulphuric acid,tobacco,gas and flammable substance , mix all this substance together and put in strong mental bottle like gas bottle put in . you must close the bottle very parked and carry that bottle carefully and shake in 5 minutes
Aaron
after shake put this bottle were the temperature is 100 degrees Celsius after moment that bottle will be high explosion like bomb
Aaron
what is mass
is object amount matter contain by object
Aaron
what is hypothesis
Aaron
hypothesis is a tentative explanation that does not have facts and it can be proven to be wrong or right
MPHO
wath is physical science
what is physics
the branch of science concerned with the nature and properties of matter and energy
Thabisto
use a vector scale diagram and represent the two displacements(5m east and 7m west)
what os covalent?
Precious
how to calculate enthalpy on a reaction?
Uapfa
how do you learn this chapter festet
it's not all about learning it fast but understanding the basics, the concepts. formulas .. if you juss understand the basics you know the chapter .understand it
Precious
you are right precious
MPHO
Uapfa
electric field around a point
The force per positive unit charge
Mpho
what is Kevlar made of ?
How do I determine the number of valence electrons for an atom
look at its group number on periodic table. group 2 elements will have 2 valence electrons and so on for all the groups. (correct me if I'm wrong but this is how I remeber it )
Siyabonga
how to find a point between to charges that is zero?