# Composition and structure

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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.

$6C{O}_{2}+6{H}_{2}O$ + sunlight $\to {C}_{6}{H}_{12}{O}_{6}+6{O}_{2}$

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.

newtons third law of motion
how to deal with newtons third law of motion
Nomvulah
help me with Newtons laws of universal gravitation
Every particle in the universe attract every other particle with a force that is directly proportional to the product of their mass and inversely proportional to the square of distance between them
Delight
guys plz help me how to calculate net force?
its FN +Fg+ Ff+ Ft+Fapplied = Net Force or any force acting on that object
Thimna
FN IS A NORMAL FORCE FG IS A GRAVITATIONAL FORCE FF IS A FRICTION FORCE FA IS A APPLIED FORCE THESE ARE FORCES THAT ACT IN EVERYTHING YOU TOUCH LIKE MUG, PEN, PHONE ,MOB EVERYTHING THAT MATTER
Simphiwe
net force is all the forces acting on an Object that is your FN +FG even T +fy or fx anyforce that will act on the object
Yanga
fnet=mass×acceleration
Yanga
What's Newton second law
Mahlatse
Newton's second law...is when 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
Cheyeza
How do yu calculate normal force on a inclined
Mahlatse
any one who can help me with chemistry
Yeah Sure. I will help
Ruthy
OK first can you pls teach me how to to calculate on chemistry chapter
george
What is a derivative?
Hulisani
Hydrocarbon derivatives are compounds that are made primarily of carbon and hydrogen atoms with specific groups of atoms attached. These specific groups of atoms are called functional groups. Hydrocarbon derivatives contain at least one element that is electronegative.
Ruthy
How to find the integral of a specific function?
Hulisani
how do u calculate the mass of an object if u have been given the gradient of a graph?
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water molecules consist of two atoms of hydrogen linked by covalent bonding to the same atom of oxygen ...hydrogen bonds are formed easily when two water molecules come close together , but are easily broken when the water molecule moves apart again
Nqobile
similarity between vander waals forces and hydrogen bond
type of intermolecular forces between 2 hydrogen and 2 oxygen
Angel
when an atom X of an element in Group 1 reacts to become X+
You have O.5 dm^3 of a KNO3 solution of concentration 0.2 M .You need to dilute this solution to get a solution of concentration 0.18M. calculate how many cubic cm of H2O you need to achieve this
Thimna
I don't know how to help i nee you help
Mphumuzi
when 3.22 moles ofAl react with 4.96 moles HBr, how many moles of H2 are formed?