Every card in Earth and atmosphere, Year 11: how the atmosphere formed
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← Back to Earth and atmosphere, Year 11: how the atmosphere formed
- One theory says that the gases of the Earth's early atmosphere were released by intense ____ activity during the Earth's first billion years.
volcanic
HintThe gases came from inside the Earth, through openings in its crust.
WhyThe same eruptions are thought to have released water vapour, and nitrogen, which slowly built up. There may also have been small amounts of methane and ammonia. This is the only theory that GCSE requires.
- In the theory that volcanoes produced the Earth's early atmosphere, which gas made up most of that atmosphere? (two words)
Carbon dioxide
HintIt is the same gas that dominates the air on Mars and Venus now.
WhyThe early atmosphere is thought to have been mainly carbon dioxide, with little or no oxygen. Today carbon dioxide is a very small part of the air (a little over 0.04%, or 420 parts per million, in 2022, NASA), so nearly all of it has been removed.
- In the theory that volcanoes produced the Earth's early atmosphere, how did the oceans form?
Water vapour released by volcanoes condensed
HintThink of what happens to steam when its surroundings cool.
WhyVolcanoes gave out water vapour along with the other gases. As the Earth cooled, the vapour condensed to liquid and collected as the oceans. Carbon dioxide then began to dissolve in them.
- Why is the evidence about the Earth's early atmosphere limited?
It existed billions of years ago — the Earth is about 4.6 billion years old
HintConsider how far into the past scientists are trying to look.
WhyNobody was there to measure it and very little survives from so long ago, so scientists rely on indirect clues such as ancient rocks and the atmospheres of other planets. That is why theories about the early atmosphere have changed and developed over time.
- The Earth's early atmosphere may have been like the atmospheres of ____ and ____ today: mainly carbon dioxide, with little or no oxygen.
Mars; Venus
HintThey are our two nearest planetary neighbours, one on each side of us.
WhyNeither planet has algae or plants, so nothing there has removed the carbon dioxide or added oxygen. They show what an atmosphere can be like when life has not changed it.
- Which type of organism first released oxygen into the Earth's atmosphere, about 2.7 billion years ago? (one word)
Algae
HintSimple water-living organisms that photosynthesise, older than land plants.
WhyAlgae were the first organisms to produce oxygen by photosynthesis, and soon afterwards oxygen began to appear in the atmosphere. Plants evolved later and added more. (Scientists often call these first oxygen-producers cyanobacteria; GCSE calls them algae.)
- About how many billion years ago did algae first produce oxygen? (number only)
2.7
HintThe Earth is about 4.6 billion years old; this happened well after it formed, between two and three billion years before now.
WhyThe Earth formed about 4.6 billion years ago, so for nearly its first two billion years there was little or no oxygen in the air. Soon after algae began to photosynthesise, oxygen started to appear in the atmosphere.
- Photosynthesis can be written as 6CO2 + 6H2O → C6H12O6 + 6O2. Use the equation to say how photosynthesis changed the amounts of two gases in the early atmosphere.
It removed carbon dioxide and added oxygen
HintOne gas is on the left of the arrow and one is on the right.
WhyCarbon dioxide is a reactant, so it is used up; oxygen is a product, so it is released. Six molecules of oxygen are released for every six molecules of carbon dioxide taken in. The reaction needs light; Biology teaches it in full.
- A pupil says: 'The oxygen in the air came out of volcanoes, like the other gases.' What is wrong with this?
Volcanoes released little or no oxygen; it was produced by photosynthesis in algae and plants
HintAsk which living things make this gas today.
WhyThe gases from volcanoes gave an atmosphere of mainly carbon dioxide. Oxygen appeared only after living things began to photosynthesise, and its percentage then rose gradually.
- Put these three events in order, earliest first: animals evolve; algae evolve; oxygen builds up in the atmosphere.
Algae evolve, then oxygen builds up, then animals evolve
HintDecide which event each of the others depended on.
WhyAlgae made the first oxygen, plants later added more, and over about a billion years the percentage rose. Only when there was enough oxygen could animals evolve.
- How did the formation of limestone help to remove carbon dioxide from the early atmosphere?
Carbon dioxide dissolved in the oceans and formed carbonates, which settled as sediment and became rock
HintStart with the gas meeting sea water, and finish on the sea bed.
WhyLimestone is mostly calcium carbonate. Some carbonate was precipitated directly, and sea creatures also used it to build shells and skeletons. These collected on the sea bed and were compressed into sedimentary rock, locking the carbon away.
- Which fossil fuel formed from the remains of plants that were buried in swamps and compressed over millions of years? (one word)
Coal
HintIt is a black solid, dug from mines.
WhyThe plants, mostly trees and ferns, had taken in carbon dioxide by photosynthesis. Buried in swamps without oxygen they could not rot, and heat and pressure slowly turned them into a sedimentary rock that is mostly carbon.
- Crude oil and natural gas formed from the remains of tiny sea organisms called ____, which were buried in mud on the sea bed.
plankton
HintThe word comes from the Greek for 'drifting'.
WhyLayers of mud and sediment covered the dead organisms and kept oxygen out. Over millions of years, heat and pressure turned the remains into crude oil and natural gas, which became trapped in the rocks.
- The plants and plankton that became fossil fuels had taken in carbon dioxide while they were alive. Why did turning into fossil fuels keep that carbon out of the atmosphere?
They were buried before they could decay, so their carbon stayed locked underground
HintNormally rotting returns it to the air; here something prevented that.
WhyPhotosynthesis moved carbon from the air into living things. Usually decay returns it, but burial without oxygen stopped that, so the carbon stayed stored for millions of years — until the fuels are burned.
- Compared with the Earth's early atmosphere, how have the proportions of carbon dioxide and oxygen changed?
Carbon dioxide has fallen to a very small proportion; oxygen has risen to about one-fifth
HintOne gas went from being the main ingredient to a trace; the other went the opposite way.
WhyEarly on the air was mainly carbon dioxide with little or no oxygen. Now it is about four-fifths nitrogen and about one-fifth oxygen, with far less than 1% carbon dioxide. Photosynthesis, and the locking of carbon into sedimentary rocks and fossil fuels, caused the change.
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