The composition and evolution of the Earth's atmosphere

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Composition of the Atmosphere Today

The atmosphere is mainly nitrogen and oxygen.
About four-fifths (80%) of the atmosphere is nitrogen.
About one-fifth (20%) is oxygen.
There are small proportions of other gases, including carbon dioxide, water vapour and noble gases.
The proportions of gases in the atmosphere have been much the same for 200 million years.
Carbon dioxide is present in very small amounts but acts as a greenhouse gas.

The Earth's Early Atmosphere

The Earth formed about 4.6 billion years ago.
The surface was molten for millions of years and had no atmosphere at first.
As the Earth cooled, land masses formed and volcanoes appeared.
Volcanoes released gases from the Earth's interior, forming the early atmosphere.
The early atmosphere was mainly carbon dioxide with little or no oxygen.
It also contained water vapour, nitrogen, and possibly methane and ammonia.
The early atmosphere may have been similar to the atmospheres of Mars and Venus today.

Formation of the Oceans

Volcanoes released large amounts of water vapour.
While the surface was very hot, water remained as a gas.
As the Earth cooled, water vapour condensed to form the oceans.
Carbon dioxide is water soluble and dissolved in the oceans.
This reduced the amount of carbon dioxide in the atmosphere.
Carbonates were precipitated and later formed sediments on the seabed.

How Oxygen Increased

Algae and plants produce oxygen by photosynthesis.
Photosynthesis uses carbon dioxide and water to produce glucose and oxygen.
The balanced equation is: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂.
Algae first evolved around 2.7 billion years ago.
Over the next billion years, plants evolved and oxygen levels increased.
Rising oxygen levels allowed more complex life forms to evolve.
Around 200 million years ago, the atmosphere reached its present composition.

How Carbon Dioxide Decreased

Carbon dioxide dissolved in the oceans when water vapour condensed.
Carbonates were precipitated, forming sediments on the seabed.
Green plants and algae absorbed carbon dioxide during photosynthesis.
Animals fed on plants, transferring carbon to their tissues, bones and shells.
When organisms died, their remains formed sedimentary rocks.
Dead organisms became fossil fuels (coal, crude oil, natural gas), locking up carbon.
These processes reduced carbon dioxide from high early levels to today's very low levels.

Formation of Limestone, Coal and Crude Oil

Limestone is formed from the shells and skeletons of marine organisms.
Coal is formed from the remains of dead plants.
Crude oil and natural gas are formed from the remains of dead marine organisms.
These deposits lock up carbon that was once in the atmosphere as carbon dioxide.
When limestone is heated (e.g. by a meteorite impact), it releases carbon dioxide: CaCO₃ → CaO + CO₂.

Evidence and Theories About the Early Atmosphere

Theories about the early atmosphere have changed over time as instrumental analysis has improved.
Evidence is limited because the early atmosphere existed 4.6 billion years ago.
Scientists use analysis of minerals in the Earth's crust to deduce gases present millions of years ago.
Historical data is less accurate due to lack of accurate instrumentation and fewer measurement locations.
Methods to estimate past climate include fossil records, tree rings, and gas bubbles in ice.
The complexity of the Earth's climate makes it difficult to model links between greenhouse gases and global warming.

Greenhouse Gases and Climate Change

Greenhouse gases absorb and store energy, trapping infrared radiation from the Earth's surface.
Carbon dioxide, methane and water vapour are greenhouse gases.
The greenhouse effect keeps the Earth's mean temperature around 15°C.
The enhanced greenhouse effect is caused by increasing levels of greenhouse gases, leading to global warming.
Carbon dioxide sources include combustion of fossil fuels, respiration, and thermal decomposition of carbonates.
Methane sources include digestive processes of animals, decomposition of vegetation, and bacterial action in swamps and rice paddies.
Climate change is a shift in worldwide weather patterns; effects include melting ice caps, flooding, and destruction of ecosystems.

Diagram showing how the greenhouse effect occurs

Human Activity and Reducing Emissions

Burning fossil fuels produces carbon dioxide: fossil fuel + oxygen → energy + H₂O + CO₂.
Deforestation increases atmospheric carbon dioxide as fewer plants remove it by photosynthesis.
Increasing agricultural activities raise methane production from animals and decomposition.
Renewable energy sources (solar, wind) can reduce carbon dioxide emissions.
Reducing energy usage and our carbon footprint helps lower emissions.
Mitigating climate change includes flood defences, new farming methods, and better irrigation systems.
About 97% of climate scientists believe human activity is causing climate change.

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1.Which option correctly shows what has happened to the proportion of each gas during the evolution of the Earth's atmosphere over the past 4.6 billion years?
Easy
- AOxygen increased, nitrogen increased, carbon dioxide decreased, water vapour decreased
- BOxygen increased, nitrogen decreased, carbon dioxide decreased, water vapour decreased
- COxygen decreased, nitrogen increased, carbon dioxide increased, water vapour increased
- DOxygen increased, nitrogen decreased, carbon dioxide increased, water vapour increased
2.What is the approximate percentage of oxygen in the current atmosphere?
Easy
- A4%
- B21%
- C55%
- D78%
3.What is the main gas in the atmosphere today?
Easy
- Aoxygen
- Bcarbon dioxide
- Cnitrogen
- Dargon
4.Which term best describes air?
Easy
- AElement
- BCompound
- CMixture
- DSolution
5.Which group of the periodic table is oxygen located in?
Easy
- AGroup 1
- BGroup 2
- CGroup 6
- DGroup 7
6.Which of the following are reasons why carbon dioxide levels have decreased since the early atmosphere? (select all that apply)
Medium
- ALocked up in fossil fuels
- BTaken in by volcanoes
- CGiven off from burning fossil fuels
- DIt dissolved in the oceans
- EProduced by photosynthesis
7.It is thought that algae evolved around 2.6 billion years ago. They use carbon dioxide and water to produce oxygen. Name the process they use to do this.
Medium
- ACombustion
- BRespiration
- CPhotosynthesis
- DDecomposition
8.What was the main source of the gases present in the early atmosphere?
Easy
- AVolcanoes
- BOceans
- CTrees
- DSediment

Soal lainnya

9.One theory is that the early atmosphere formed 4.6 billion years ago. Which gas was the main gas present?
Medium
- ACarbon dioxide
- BOxygen
- CNitrogen
- DArgon
10.Which of the following are natural processes by which plants and marine life remove carbon dioxide from the atmosphere? (select all that apply)
Medium
- APhotosynthesis by green plants and algae
- BDissolving in the oceans
- CFormation of carbonate sediments
- DRespiration
- ECombustion of fossil fuels
11.Since the early atmosphere, water vapour levels have decreased. Which of the following is another difference between the early atmosphere and the atmosphere today?
Medium
- AOxygen levels have increased and carbon dioxide levels have decreased.
- BOxygen levels have decreased and carbon dioxide levels have increased.
- CBoth oxygen and carbon dioxide levels have increased.
- DBoth oxygen and carbon dioxide levels have decreased.
12.The proportion of gases in the air has not changed much in 200 million years.
Easy
True or false?
13.The early atmosphere contained large amounts of oxygen.
Easy
True or false?
14.Carbon dioxide is a water-soluble gas that dissolves readily in water.
Easy
True or false?
15.Theories about the early atmosphere are certain because scientists have directly measured the gases present 4.6 billion years ago.
Medium
True or false?
16.Match each gas to its approximate percentage in the current atmosphere.
Medium
- Nitrogen
- Oxygen
- Carbon dioxide
- Argon
- 78%
- 21%
- 0.04%
- 0.96%
17.Place the following events in the evolution of the Earth's atmosphere in the correct order, from earliest to latest.
Medium
- Volcanoes release carbon dioxide, water vapour and nitrogen
- Water vapour condenses to form the oceans
- Carbon dioxide dissolves in the oceans and forms carbonate sediments
- Algae and plants photosynthesise, increasing oxygen levels
- Atmosphere reaches its present composition
18.Which of the following best explains why carbon dioxide levels decreased when the oceans formed?
Medium
- ACarbon dioxide dissolved in the oceans and carbonates were precipitated, forming sediments.
- BCarbon dioxide reacted with oxygen to form carbonates.
- CCarbon dioxide was broken down by sunlight into carbon and oxygen.
- DCarbon dioxide was absorbed by volcanoes.
19.Which of the following is a reason why theories about the Earth's early atmosphere have changed over time?
Medium
- AInstrumental analysis has improved, providing better evidence.
- BThe early atmosphere has been directly sampled.
- CScientists have stopped studying the atmosphere.
- DThe composition of the atmosphere has remained constant.
20.What is the main gas on Mars?
Medium
- ACarbon dioxide
- BNitrogen
- CArgon
- DOxygen
21.Which gas in the table is a compound?
Medium
- ACarbon dioxide
- BNitrogen
- CArgon
- DOxygen
22.Which gas in the table is a noble gas?
Medium
- AArgon
- BNitrogen
- COxygen
- DCarbon dioxide
23.Which of the following gases were released into the early atmosphere by intense volcanic activity during the first billion years of Earth's history? (Select all that apply.)
Medium
- ACarbon dioxide
- BWater vapour
- COxygen
- DNitrogen
- EAmmonia
24.Which of the following statements about the early atmosphere are correct? (Select all that apply.)
Medium
- AIt contained little or no oxygen.
- BIt was mainly carbon dioxide.
- CIt contained about 20% oxygen.
- DIt contained water vapour.
- EIt contained about 80% nitrogen.
25.Which of the following are ways in which carbon became locked up in rocks or fossil fuels, reducing the amount of carbon dioxide in the atmosphere? (Select all that apply.)
Medium
- ACarbon dioxide dissolved in the oceans and formed carbonate sediments.
- BMarine organisms used carbonates to build shells and skeletons.
- CDead organisms were buried and formed coal, crude oil and natural gas.
- DVolcanoes released carbon dioxide into the atmosphere.
- EPlants released carbon dioxide during respiration.
26.Which of the following statements explain why theories about the Earth's early atmosphere have changed over time? (Select all that apply.)
Hard
- AInstrumental analysis has improved.
- BEvidence about the early atmosphere is limited because it formed 4.6 billion years ago.
- CScientists have directly measured gases from 4.6 billion years ago.
- DNew evidence from analysing minerals in the Earth's crust can be used to deduce gases present millions of years ago.
- EThe early atmosphere is identical to today's atmosphere.
27.Match each gas to the process or source that removed it from the early atmosphere.
Medium
- Carbon dioxide
- Water vapour
- Carbon (in fossil fuels)
- Condensed to form oceans
- Dissolved in oceans and formed carbonate sediments
- Locked up in dead organisms buried underground
28.Arrange the steps in the process that decreased carbon dioxide in the early atmosphere into the correct order.
Medium
- Water vapour condenses to form oceans.
- Carbon dioxide dissolves in the oceans.
- Carbonates precipitate and form sediments.
- Marine organisms use carbonates for shells and skeletons.
- Dead organisms are buried and form fossil fuels.
29.Which process is mainly responsible for the increase in oxygen in the Earth's atmosphere?
Easy
- ARespiration
- BCombustion
- CPhotosynthesis
- DVolcanic eruption
30.Approximately when did algae first evolve and begin producing oxygen?
Medium
- A2.7 billion years ago
- B200 million years ago
- C4.6 billion years ago
- D60 million years ago
31.A student heats copper in a sealed syringe containing 50.0 cm³ of air until the copper turns black, then allows the apparatus to cool. The final volume of gas is 39.5 cm³. What is the percentage of oxygen in the air sample?
Medium
- A21.0%
- B10.5%
- C79.0%
- D26.6%
32.In the copper-and-syringe experiment to find the percentage of oxygen in air, the copper turns black. What does this show?
Medium
- ACopper has reacted with oxygen to form copper oxide
- BCopper has melted because of the Bunsen flame
- CCopper has reacted with nitrogen to form a nitride
- DCopper has absorbed water vapour from the air
33.A student passes a known volume of air over heated copper several times, but the final volume is 46.0 cm³ from a starting volume of 50.0 cm³. Which is the most likely explanation for the result?
Medium
- AThe air was not passed over the copper enough times, so not all the oxygen reacted
- BThe copper reacted with nitrogen instead of oxygen
- CThe apparatus leaked and extra air entered
- DThe copper was not heated, so no reaction occurred at all
34.Table 1 compares the atmospheres of Mars and Earth today. Mars: carbon dioxide 95.00%, nitrogen 3.50%, argon 1.00%, oxygen 0.50%. Earth: carbon dioxide 0.04%, nitrogen 78.00%, argon 0.96%, oxygen 21.00%. Which statement is best supported by the data?
Medium
- AEarth's atmosphere contains far more oxygen than Mars's, while Mars's is dominated by carbon dioxide
- BEarth and Mars have similar proportions of carbon dioxide
- CMars's atmosphere contains more nitrogen than Earth's
- DThe two atmospheres have almost identical compositions
35.The early Earth's atmosphere is thought to have contained about 95% carbon dioxide. The atmosphere today contains about 0.04% carbon dioxide. Which calculation gives the decrease in the percentage of carbon dioxide?
Hard
- A95 − 0.04 = 94.96 percentage points
- B95 ÷ 0.04 = 2375 percentage points
- C0.04 − 95 = −94.96 percentage points
- D95 × 0.04 = 3.8 percentage points
36.In the copper-and-syringe experiment, the volume of gas measured after the reaction is the volume of air with the oxygen removed.
Easy
True or false?
37.Analysis of gas bubbles trapped in ice from hundreds of thousands of years ago can be used to estimate past levels of carbon dioxide in the atmosphere.
Medium
True or false?
38.Match each observation from the copper-and-syringe experiment to what it shows.
Medium
- Copper turns black
- Final gas volume is lower than the starting volume
- A glowing splint relights in the gas collected
- Copper has reacted with oxygen
- Oxygen has been removed from the air
- The gas collected is oxygen
39.Place the steps of the copper-and-syringe experiment to find the percentage of oxygen in air in the correct order.
Medium
- Heat the copper using a Bunsen burner
- Push the plunger to force the air back and forth over the copper several times
- Allow the apparatus to cool
- Record the volume of gas remaining in one syringe
40.A graph shows the percentage of carbon dioxide in the atmosphere rising from about 0.032% to about 0.042% over 50 years. Why are scientists concerned about this trend?
Medium
- ACarbon dioxide is a greenhouse gas, so rising levels increase the enhanced greenhouse effect and global warming
- BCarbon dioxide is toxic to humans at these concentrations
- CCarbon dioxide reacts with nitrogen and removes it from the air
- DCarbon dioxide has no effect on the Earth's temperature
41.Complete the word equation for photosynthesis.
Medium
____ + water → ____ + oxygen
42.There was 95% carbon dioxide present in the Earth's early atmosphere. The current level is 0.04%. Calculate the decrease in carbon dioxide levels, in percentage points.
Medium
43.Name two other gases that were present in the early atmosphere.
Easy
44.Complete the sentences using the words in the box to describe what happened to the water vapour in the early atmosphere. Words: increased, ocean, decreased, volcanoes, evaporated, condensed.
Medium
The temperature of the earth's surface ____. The water vapour in the air ____ to form the ____.
45.Name the process by which algae and plants produced oxygen in the atmosphere.
Easy
46.Name the type of organism first responsible for producing oxygen on Earth.
Medium
47.In an experiment, the starting volume of air was 50.0 cm³ and the final volume of air was 39.5 cm³. Calculate the percentage of oxygen in the air.
Medium
48.Complete the sentence about the present composition of the atmosphere.
Medium
About four-fifths of the atmosphere is ____ and about one-fifth is ____.
49.Complete the sentences using the words in the box. Words: increased, ocean, decreased, volcanoes, evaporated, condensed.
Medium
The temperature of the earth's surface ____. The water vapour in the air ____ to form the ____.
50.Name the process by which algae and plants produced oxygen in the early atmosphere.
Easy
51.Complete the sentences about the formation of the oceans using the words below.
Medium
When the Earth cooled, water vapour in the atmosphere ____ to form the ____.
52.In an experiment, the starting volume of air was 50.0 cm³ and the final volume of air was 39.5 cm³. Calculate the percentage of oxygen in the air. Give your answer to 3 significant figures.
Medium
53.Oxygen levels have increased over the past 4.5 billion years. Explain why.
Medium
54.Carbon dioxide levels have decreased since the early atmosphere. Give three reasons why.
Hard
55.Describe how the gases in Earth's early atmosphere (in the first billion years) formed.
Hard
56.Explain why the levels of carbon dioxide in the Earth's early atmosphere decreased over billions of years.
Hard
57.A student says the copper-and-syringe experiment proves that air contains exactly 21% oxygen. Evaluate this statement, referring to the method and the data obtained.
Hard
58.There was 95% carbon dioxide present in the Earth's early atmosphere. The current level is 0.04%. Calculate the decrease in carbon dioxide levels, in percentage points.
Medium
- A85.46 %
- B104.46 %
- C113.96 %
- D94.96 %
59.In an experiment, the starting volume of air was 50.0 cm³ and the final volume of air was 39.5 cm³. Calculate the percentage of oxygen in the air.
Medium
- A23 %
- B21 %
- C25 %
- D19 %
60.In an experiment, the starting volume of air was 50.0 cm³ and the final volume of air was 39.5 cm³. Calculate the percentage of oxygen in the air. Give your answer to 3 significant figures.
Medium
- A21 %
- B19 %
- C23 %
- D25 %

Kartu flash

What are the approximate proportions of nitrogen and oxygen in today's atmosphere?

About four-fifths (approximately 80%) nitrogen and about one-fifth (approximately 20%) oxygen.

Besides nitrogen and oxygen, which gases are present in small proportions in today's atmosphere?

Carbon dioxide, water vapour and trace quantities of the noble gases.

For how long have the proportions of gases in the atmosphere been much the same as they are today?

For about 200 million years.

Why is evidence about the Earth's early atmosphere limited?

It formed about 4.6 billion years ago, so it is very difficult to gather evidence about it.

What was the surface of the early Earth like for millions of years, and what does this mean for the atmosphere?

The surface was molten for millions of years, during which time there was no atmosphere.

How did land masses and volcanoes form on the early Earth?

As the Earth cooled, the molten surface slowly solidified into land masses, and volcanoes formed on them.

What is one theory for how the early atmosphere formed?

Intense volcanic activity released gases from the Earth's interior through violent eruptions, and Earth's gravity prevented these gases from escaping, so they formed the atmosphere.

Which gases did volcanic eruptions release into the early atmosphere?

Large amounts of carbon dioxide and water vapour, as well as nitrogen, hydrogen and other gases which may have included small proportions of ammonia and methane.

Which planets' atmospheres today are thought to be similar to the Earth's early atmosphere?

Mars and Venus, which consist mainly of carbon dioxide.

What was the main gas in the Earth's early atmosphere, and how much oxygen was present?

The early atmosphere was mainly carbon dioxide, with little or no oxygen present.

Why did water vapour remain a gas in the early atmosphere, and what happened when conditions cooled?

The surface was still very hot, so water vapour stayed gaseous; when it cooled sufficiently the water vapour condensed and fell to the surface, forming the oceans.

Why does carbon dioxide dissolve readily in the oceans?

Carbon dioxide is a water soluble gas (it is the gas used in fizzy drinks), so when the water vapour condensed, large amounts of CO2 dissolved in the oceans.

What happened to dissolved carbon dioxide in the early oceans?

Carbonate substances were precipitated, which later formed sediments on the seabed, reducing the carbon dioxide in the atmosphere.

Which organisms first produced oxygen in the atmosphere, and when?

Algae, which first evolved around 2.7 billion years ago and began photosynthesising.

How did photosynthesis change the atmosphere over billions of years?

It used up carbon dioxide and released oxygen, so oxygen levels increased and carbon dioxide levels decreased.

What is the word equation for photosynthesis?

Carbon dioxide + water → glucose + oxygen.

What is the balanced symbol equation for photosynthesis?

6CO2 + 6H2O → C6H12O6 + 6O2.

Why was the rise in oxygen important for life on Earth?

As oxygen levels increased, it allowed more complex life forms, including animals, to evolve.

Give three ways carbon dioxide was removed from the early atmosphere.

It dissolved in the oceans when water vapour condensed (forming carbonate sediments), it was absorbed by green plants and algae during photosynthesis, and carbon was locked up in sedimentary rocks and fossil fuels.

How did animals help transfer carbon into sedimentary rocks?

Animals fed on plants, transferring carbon to their tissues including bones and shells; when they died their remains formed sedimentary rocks.

How are fossil fuels such as crude oil, natural gas and coal formed?

Dead organisms were buried and their remains turned into fossil fuels, which 'locked up' the carbon.

What is the test for oxygen gas?

Place a glowing splint inside a test tube of the gas; if it is oxygen the splint will relight.

How can the percentage of oxygen in air be found using copper?

Pass a known volume of air over heated copper; the copper turns black as it reacts to form copper oxide, removing the oxygen, then measure the volume decrease.

In an experiment, 50.0 cm3 of air fell to 39.5 cm3 after the oxygen was removed. What is the percentage of oxygen?

(50.0 − 39.5) ÷ 50.0 × 100 = 21.0%.

Why have theories about the Earth's early atmosphere changed over time?

They have altered and developed as instrumental analysis has improved, allowing better interpretation of evidence.

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