Chemistry - Earth's Atmosphere (AQA)
The amount of carbon dioxide in the atmosphere has increased dramatically due to the development of the motor car.

Chemistry - Earth's Atmosphere (AQA)

One topic looked at in GCSE Science is the changes which have and do occur on the Earth and in its atmosphere. This is the second of three quizzes on the subject and it focusses specifically on the Earth's atmosphere and the gases found there.

Something that you probably take for granted is the atmosphere around us and the gases that we breathe. But the atmosphere doesn't only supply the oxygen that our bodies need for respiration, it also protects us from space. High level ozone protects us from the effects of the most harmful ultra-violet rays from the Sun and carbon dioxide ensures that the Earth's temperature stays within the limits needed for life. The atmosphere also protects us from most fragments of space debris by causing them to burn up well before they hit the Earth's surface and it allows water and carbon to be recycled through food chains.

But how did the atmosphere get here and how has it ended up as being perfect to sustain life? These are questions that can't be answered with certainty as it all happened long ago in the distant past. It seems that our atmosphere has been pretty much the same mixture of gases for about 200 million years!

Scientists have many theories as to how the atmosphere was formed and how changes have occurred over time. The most widely accepted is the one that suggests it came from volcanic activity. Molten magma contains a lot of gas dissolved in it which is released when it erupts at the surface. The early atmosphere was probably mostly carbon dioxide with little or no oxygen. There were smaller proportions of water vapour, ammonia and methane. As the Earth cooled down, most of the water vapour condensed and formed the oceans. The atmospheres of Venus and Mars are thought to be like the Earth's early atmosphere but the changes which happened on Earth never took place on those planets.

As well as the main gases, which of the following are found in the atmosphere in small proportions?
Carbon dioxide
Water vapour
All of the above
About 0.9% of the air you breathe is argon
About how much oxygen is there in the atmosphere?
Only about a fifth of the atmosphere is life-sustaining oxygen
About how much of the atmosphere is nitrogen?
You are expected to know the proportions of the gases in the atmosphere for the exam
The level of carbon dioxide in the atmosphere has remained almost the same for 200 million years. Since the start of the twentieth century it has increased dramatically. What is thought to have caused this?
The increase in population
The development of the motor car
Nuclear power stations
The steel making industry
The curve showing the increase of carbon dioxide seems to have followed the development of the motor car. As cars have become more affordable, millions more have appeared on the roads, burning huge amounts of fossil fuels and releasing carbon dioxide that has been locked away for millions of years
Argon is a noble gas and is inert (does not react with other substances). For that reason it is used in light bulbs but how is it obtained from the air?
The air is solidified and argon is collected as the solid air sublimes
The air is liquified and argon can be collected by fractional distillation
It can be filtered out from the air by using a special filter
It is made from other chemicals
Air is a mixture of gases so if you cool it down enough, it will turn into a mixture of liquids that can be separated by fractional distillation
The first green algae-like plants evolved about 2,000 million years ago. How would this have affected the early atmosphere?
It reduced the carbon dioxide levels and increased the amount of oxygen
It started to fix nitrogen into the soil
It converted methane into ammonia which was then converted to oxygen by animals
It would not have caused any changes to the early atmosphere
Photosynthesis by the earliest plants is thought to have converted a lot of the carbon dioxide into oxygen
One theory is that life on Earth started from chemicals in the early atmosphere. According to that theory, which chemicals are thought to have been involved?
Methane and carbon dioxide
Ammonia and oxygen
Ammonia and hydrocarbons
Hydrocarbons and oxygen
It has been suggested that lightning provided the energy for the chemical reactions to take place
What natural process is thought to have created the early atmosphere and which was the main gas?
Volcanic action created the early atmosphere and carbon dioxide was the main gas
Photosynthesis created the early atmosphere and oxygen was the main gas
Cosmic rays created the early atmosphere and nitrogen was the main gas
Global warming created the early atmosphere and carbon dioxide was the main gas
The early Earth was a much more volcanically active place than it is now
Why is nitrogen used in food packaging?
It makes the food lighter and easier to transport
It is cheaper than using all of the air
It makes food taste a lot better
It is unreactive and helps to keep the food fresher
Food goes off because it is exposed to oxygen and microorganisms. If nitrogen is used instead of air, there is no oxygen so the food is less likely to spoil before it reaches you since the bacteria can't thrive
What may have happened to the rest of the carbon dioxide from the early atmosphere?
It has been lost into space
It has been changed into other gases by radiation from the Sun
It was absorbed by the oceans and then has been locked into rocks like limestone
It has been absorbed by lava from volcanoes
Limestone is made under the sea from the mineral calcium carbonate and its formation required carbon dioxide. Carbonate containing rocks form on the sea bed
You can find more about this topic by visiting BBC Bitesize - Chemistry of the atmosphere

Author:  Kev Woodward

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