The Earth's early atmosphere

For the first billion years the young Earth was a violent place. Intense volcanic activity released gases that are thought to have formed the very first atmosphere:

• It was rich in carbon dioxide (CO₂), with little or no oxygen — similar to the atmospheres of Mars and Venus today.
• Volcanoes also released large amounts of water vapour, plus smaller amounts of nitrogen, methane and ammonia.
• As the Earth cooled, the water vapour condensed and fell as rain, forming the early oceans.

Watch out: the early atmosphere was not breathable. There was almost no oxygen — that came much later, and from living things.

What released the early atmosphere?

How an oxygen-rich atmosphere developed

Over geological time two big changes happened: oxygen went up and carbon dioxide came down.

Oxygen increased because of life:

• About 2.7 billion years ago, algae evolved, followed later by plants.
• They carried out photosynthesis, taking in CO₂ and releasing oxygen.

Carbon dioxide decreased by several routes:

• It dissolved into the newly formed oceans.
• Marine organisms used dissolved CO₂ to build carbonate shells; these formed sedimentary rocks (e.g. limestone).
• Carbon was locked away in fossil fuels (coal, oil, gas) made from the remains of dead organisms.
• Photosynthesis also removed CO₂ from the air.

Misconception fix: the oxygen in our air did not come from volcanoes or rocks — it was produced by photosynthesis in algae and plants over billions of years.

Up or down?

For each process, tap whether it made oxygen rise or carbon dioxide fall.

The present-day composition

For the last 200 million years the composition of the air has been roughly stable. You should recall the approximate proportions:

Handy check: nitrogen + oxygen alone make up about 99% of dry air. Everything else — argon, CO₂ and the other noble gases — shares the last ~1%.

Your turn — what's left over?

Where did the early carbon dioxide go?

What stops some energy escaping to space?

Why the Earth stays warm

The greenhouse effect is a natural and essential process — without it the Earth would be far too cold for life. Eduqas wants you to describe it in terms of how radiation interacts with the atmosphere:

• Short-wavelength sunlight passes through the atmosphere and warms the surface.
• The warm Earth re-emits energy as longer-wavelength infrared radiation.
• Greenhouse gases — carbon dioxide, methane and water vapour — absorb this re-radiated infrared and re-emit it in all directions, including back to the surface, keeping the Earth warm.

Misconception fix: the greenhouse effect itself is natural and needed. The greenhouse gases absorb the Earth's re-radiated infrared — they do not trap incoming sunlight, and they are not "holes in the ozone layer" (a different topic).

Spot the greenhouse gas

The enhanced greenhouse effect

Human activities are adding extra greenhouse gases to the atmosphere. This strengthens the natural greenhouse effect — Eduqas calls this the enhanced greenhouse effect, and it is the cause of global warming.

• More carbon dioxide — chiefly from burning fossil fuels, plus deforestation (fewer trees to remove CO₂).
• More methane — from livestock (cattle), rice paddies and landfill / decomposing waste.

More greenhouse gas means more of the Earth's outgoing infrared is absorbed, so the lower atmosphere warms — this is global warming.

What stops some energy escaping to space?

The evidence — and its uncertainties

Eduqas asks you to evaluate the evidence for human-caused climate change, not just recall it. The key piece of evidence is a correlation:

• Measurements show atmospheric CO₂ concentration has risen alongside the consumption of fossil fuels, and average global temperature has risen too.
• This is supported by ice-core records, peer-reviewed studies and many independent datasets.

But good scientists also describe the uncertainties:

• The climate is complex, with many interacting factors, so models give a range of predictions rather than one exact figure.
• Correlation on its own does not prove cause — though here it is backed by a well-understood physical mechanism (greenhouse gases absorbing infrared).
• Findings must be peer-reviewed and reported honestly, separating evidence from opinion and media bias.

Thinking like a scientist

Effects of more CO₂ and methane — and how to reduce them

Eduqas (g) asks you to describe the potential effects of increased CO₂ and methane, and how they may be mitigated, weighing up scale, risk and environmental implications.

Potential effects of a warmer climate:

• Melting of ice sheets and glaciers, leading to rising sea levels and coastal flooding.
• More frequent extreme weather and changes to rainfall patterns affecting farming.
• Changes to habitats and the distribution of species.

Ways to mitigate (reduce) emissions:

• Switching from fossil fuels to renewable energy.
• Improving energy efficiency and reducing waste.
• Planting trees and protecting forests so more CO₂ is removed.
• Carbon capture and storage of CO₂ from power stations.

Evaluate, don't panic: every measure has costs as well as benefits. Decisions weigh the scale of the change, the risk of acting too slowly, and the economic and societal impacts — that balance is exactly what examiners want you to discuss.

Which one cuts CO₂?

Where does the nitrogen in exhaust come from?

Other pollutants and their problems

Burning fuels (especially fossil fuels) releases more than just CO₂. Eduqas (h) wants the major sources and problems of these pollutants:

• Carbon monoxide (CO) — from incomplete combustion (too little oxygen). A toxic, colourless, odourless gas; it binds to haemoglobin so the blood carries less oxygen.
• Sulfur dioxide (SO₂) — from sulfur impurities in fuels. Causes acid rain and irritates the lungs.
• Oxides of nitrogen (NOₓ) — formed at the high temperatures inside engines (nitrogen + oxygen react). Cause acid rain, photochemical smog and respiratory problems.
• Particulates — tiny carbon (soot) and unburnt particles from incomplete combustion. Cause respiratory problems and global dimming.

Pollutant → problem

Tap a pollutant, then tap the problem it causes.

Where does the nitrogen in exhaust come from?

Making water safe to drink

Topic 12 finishes (statement i) with potable water — water that is safe to drink (low in dissolved salts and microbes; it does not have to be pure). You should know the main methods and how easy each is to treat:

• Fresh / ground water (easiest): filtration to remove solids, then sterilisation (with chlorine, ozone or UV) to kill microbes.
• Waste water (sewage): screened, then settled into sludge, then biologically treated before release.
• Salt water / sea water (hardest, used where fresh water is scarce): desalination by distillation or reverse osmosis — both need a lot of energy.

Key distinction: potable water is safe to drink, not pure (pure water contains only H₂O molecules). Salt water is the hardest to treat because removing dissolved salts needs energy-intensive desalination.

Which is hardest to treat?

Topic 12 in a nutshell

You've covered the key ideas in Eduqas Topic 12 — the origin and evolution of the atmosphere, the greenhouse effect and climate change, air pollutants and potable water. Press Finish to see your score.