The Earth and its Atmosphere
The Earth's atmosphere is the layer of gases surrounding the planet, made up today of about 78% nitrogen, 21% oxygen and small amounts of other gases including carbon dioxide and argon. Its composition has changed hugely over 4.6 billion years, from mostly carbon dioxide and water vapour to today's oxygen-rich mix. This KS3 topic also covers the greenhouse effect and human impact on the atmosphere.
Before you start
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Method
- Learn today's approximate atmospheric composition: about 78% nitrogen, 21% oxygen, and small amounts of other gases (about 0.04% carbon dioxide, just under 1% argon, plus trace gases).
- Recall that the early atmosphere, formed by volcanic activity, was mostly carbon dioxide and water vapour with little or no oxygen.
- Explain how oceans formed as water vapour condensed, and how photosynthesising organisms (cyanobacteria, then plants) gradually removed carbon dioxide and released oxygen over billions of years.
- Describe the greenhouse effect: the Sun's radiation warms the Earth's surface, the surface radiates infrared radiation, and greenhouse gases absorb and re-radiate this radiation, keeping the surface warmer.
- Link human activities such as burning fossil fuels and deforestation to rising concentrations of greenhouse gases like carbon dioxide and methane, and to the enhanced greenhouse effect (global warming).
- Practise calculating percentage changes and rates from atmospheric data tables, such as CO2 concentration over time, and interpreting carbon footprint data.
Worked example
The table shows atmospheric CO2 concentration: 1970 = 325 ppm, 2020 = 415 ppm. Calculate the percentage increase in CO2 concentration from 1970 to 2020. Give your answer to 1 decimal place.
- Find the increase in concentration: 415 - 325 = 90 ppm.
- Divide the increase by the original (1970) value: 90 / 325.
- Multiply by 100 to convert to a percentage: (90 / 325) x 100 = 27.69...
- Round the answer to 1 decimal place.
- Final answer: 27.7% increase.
Practice questions
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Q1State the gas that makes up approximately 78% of today's atmosphere.Show answer
Answer: Nitrogen
Q2State the approximate percentage of oxygen in today's atmosphere.Show answer
Answer: 21%
Q3Name the process by which early volcanic activity released gases to form the early atmosphere.Show answer
Answer: Volcanic activity (outgassing)
Q4Name two greenhouse gases whose atmospheric concentration has increased mainly due to human activity.Show answer
Answer: Carbon dioxide and methane
Q5Atmospheric CO2 concentration rose from 340 ppm in 1980 to 420 ppm in 2020. Calculate the mean rate of increase, in ppm per year, to 2 decimal places.Show answer
Answer: 2.00 ppm per year (80 divided by 40)
Q6A return flight produces 580 kg CO2e and the equivalent car journey produces 145 kg CO2e. Determine how many times more CO2e the flight produces than the car journey.Show answer
Answer: 4 times (580 divided by 145)
Exam-style questions
Written in the style of a KS3 Science exam paper, with a full mark scheme.
A student investigates the percentage of oxygen in air by passing air repeatedly over heated copper in a sealed tube connected to two gas syringes, until the volume stops changing. She records a starting volume of 100 cm3 of air. Once the tube has cooled fully to room temperature, the final volume remaining is 80 cm3. Calculate the percentage of oxygen in the air sample. Show your working.
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Two neighbouring households book the same return flight, which produces 640 kg of CO2e. One household then drives to the airport, adding 28 kg of CO2e for the car journey. The other household instead catches a train to the airport, adding only 5 kg of CO2e. Calculate the difference between the two households' total carbon footprints for their trip.
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Explain what is meant by the greenhouse effect, and explain how an increase in human-produced greenhouse gases leads to global warming (the enhanced greenhouse effect).
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Free printable worksheet
Want more practice on paper? Download the the earth and its atmosphere worksheet pack - 19 pages of exam-style questions with a full mark scheme. One email opens every download in this browser for 14 days - no account, no card. Print it for personal and classroom use.
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