What is the approximate composition of today's atmosphere?

The atmosphere is approximately 80% nitrogen and 20% oxygen , with small proportions of carbon dioxide, water vapour, and trace amounts of noble gases. This composition has been stable for around 200 million years.

What percentage of the atmosphere is nitrogen , and what percentage is oxygen ?

Nitrogen makes up approximately 80% of the atmosphere. Oxygen makes up approximately 20% . These proportions have remained relatively constant for around 200 million years.

True or False? Oxygen makes up approximately 80% of the atmosphere.

False. Nitrogen makes up approximately 80% (four-fifths) of the atmosphere. Oxygen makes up approximately 20% (one-fifth). Confusing the proportions of nitrogen and oxygen is a common error.

Complete the composition of the atmosphere: Gas Approximate amount Nitrogen Oxygen Carbon dioxide Water vapour Noble gases

Gas Approximate amount Nitrogen 80% Oxygen 20% Carbon dioxide Small amounts (~0.04%) Water vapour Small amounts Noble gases Trace amounts

Why is carbon dioxide important in the atmosphere despite being present in only a very small proportion?

Carbon dioxide is a greenhouse gas that plays a substantial role in global warming . Even small increases in CO 2 concentration can significantly affect the climate by trapping heat energy in the atmosphere.

What gases did volcanic eruptions release to form the early atmosphere?

Volcanoes released large amounts of carbon dioxide and water vapour , as well as nitrogen and hydrogen , with possibly small proportions of ammonia and methane . Little or no oxygen was present.

Why is it difficult to gather reliable evidence about the early atmosphere ?

The early atmosphere formed approximately 4.6 billion years ago . Over such a vast timescale, physical evidence has been altered or destroyed, and there are no direct measurements. Scientists rely on indirect evidence and theoretical models.

True or False? The early atmosphere of Earth was rich in oxygen .

False. The early atmosphere was dominated by carbon dioxide and water vapour from volcanic activity. Oxygen was not present in significant amounts until photosynthesis by early plants and algae began.

How did the oceans form on early Earth?

The early Earth was very hot, so water vapour remained as a gas. As the Earth gradually cooled , water vapour condensed and fell to the surface, accumulating to form the oceans.

How did CO 2 levels in the early atmosphere decrease as oceans formed?

Carbon dioxide is water-soluble and dissolved in large amounts into the new oceans. Carbonate substances were precipitated and formed sediments on the ocean floor. This process significantly reduced the amount of CO 2 in the atmosphere.

Volcanic eruptions released large amounts of ________ and water ________ , plus ________ and hydrogen, with possible small amounts of ammonia and methane.

Volcanic eruptions released large amounts of carbon dioxide and water vapour , plus nitrogen and hydrogen, with possible small amounts of ammonia and methane.

How did oxygen levels in the atmosphere increase over time?

Primitive algae and later plants began photosynthesising , absorbing carbon dioxide and releasing oxygen . As plant life spread over billions of years, oxygen levels gradually increased, reaching today's ~20% around 200 million years ago.

Which organisms first caused oxygen levels in the atmosphere to rise, and when did they appear?

Algae first evolved approximately 2.7 billion years ago and began photosynthesising. Over the following billion years, small green plants also appeared, further increasing oxygen levels. This allowed more complex life forms to evolve.

True or False? Oxygen has always made up approximately 20% of the atmosphere.

False. The early atmosphere contained little or no oxygen. Oxygen increased gradually through photosynthesis by algae and plants over billions of years. The atmosphere only reached its current composition (20% O 2 ) approximately 200 million years ago .

What is the balanced symbol equation for photosynthesis ?

Plants and algae use light energy to convert carbon dioxide and water into glucose and oxygen: 6CO 2 + 6H 2 O → C 6 H 12 O 6 + 6O 2 This reaction was responsible for the long-term increase in atmospheric oxygen.

Primitive ________ and later ________ began photosynthesising, absorbing ________ from the atmosphere and releasing ________ .

Primitive algae and later plants began photosynthesising, absorbing carbon dioxide from the atmosphere and releasing oxygen .

Give three ways that carbon dioxide levels decreased from the early atmosphere.

CO 2 dissolved in the oceans and carbonates precipitated, forming sedimentary rocks . Photosynthesis by plants and algae absorbed CO 2 and released O 2 . Dead organisms became compressed over millions of years into fossil fuels , locking carbon away.

How did the newly formed oceans cause CO 2 levels to fall?

CO 2 is water-soluble and dissolved into the oceans in large amounts. Carbonate substances were then precipitated and accumulated as sediments, which over time formed sedimentary rocks . This removed CO 2 from the atmosphere permanently.

True or False? Coal formed when carbon dioxide gas was compressed underground.

False. Plants and algae absorbed CO 2 during photosynthesis , incorporating the carbon into their tissues. When these organisms died, their remains were compressed over millions of years to form fossil fuels. The carbon in coal came from living organisms, not directly from compressed CO 2 gas.

What happened to the carbon absorbed by animals that ate plants in the early Earth?

Animals incorporated carbon into their bones and shells . When these organisms died, their remains formed sedimentary rocks , permanently storing carbon. This was another route by which CO 2 was removed from the atmosphere.

Why is the step " carbonates precipitated " important when explaining how CO 2 decreased as oceans formed?

Simply stating "CO 2 dissolved in the oceans" often gains only one mark. To access the second mark, you must state that carbonate substances were precipitated and formed sediments (or sedimentary rocks). This step shows the CO 2 was permanently removed, not just dissolved.

CO 2 levels decreased because it ________ in the oceans forming carbonate ________ , was absorbed by plants during ________ , and carbon was locked up in ________ fuels.

CO 2 levels decreased because it dissolved in the oceans forming carbonate sediments , was absorbed by plants during photosynthesis , and carbon was locked up in fossil fuels.

GCSEScienceAQACombined Science: TrilogyChemistryFlashcardsChemistry of the AtmosphereFormation of Earth's Atmosphere

Formation of Earth's Atmosphere (AQA GCSE Combined Science: Trilogy: Chemistry): Flashcards

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What is the approximate composition of today's atmosphere?

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What is the approximate composition of today's atmosphere?
The atmosphere is approximately 80% nitrogen and 20% oxygen, with small proportions of carbon dioxide, water vapour, and trace amounts of noble gases.
This composition has been stable for around 200 million years.
What percentage of the atmosphere is nitrogen, and what percentage is oxygen?
Nitrogen makes up approximately 80% of the atmosphere.
Oxygen makes up approximately 20%.
These proportions have remained relatively constant for around 200 million years.
True or False?
Oxygen makes up approximately 80% of the atmosphere.
False.
Nitrogen makes up approximately 80% (four-fifths) of the atmosphere.
Oxygen makes up approximately 20% (one-fifth).
Confusing the proportions of nitrogen and oxygen is a common error.
Complete the composition of the atmosphere:
Gas
Approximate amount
Nitrogen
Oxygen
Carbon dioxide
Water vapour
Noble gases
Gas
Approximate amount
Nitrogen
80%
Oxygen
20%
Carbon dioxide
Small amounts (~0.04%)
Water vapour
Small amounts
Noble gases
Trace amounts
Why is carbon dioxide important in the atmosphere despite being present in only a very small proportion?
Carbon dioxide is a greenhouse gas that plays a substantial role in global warming.
Even small increases in CO₂ concentration can significantly affect the climate by trapping heat energy in the atmosphere.
What gases did volcanic eruptions release to form the early atmosphere?
Volcanoes released large amounts of carbon dioxide and water vapour, as well as nitrogen and hydrogen, with possibly small proportions of ammonia and methane. Little or no oxygen was present.
Why is it difficult to gather reliable evidence about the early atmosphere?
The early atmosphere formed approximately 4.6 billion years ago.
Over such a vast timescale, physical evidence has been altered or destroyed, and there are no direct measurements. Scientists rely on indirect evidence and theoretical models.
True or False?
The early atmosphere of Earth was rich in oxygen.
False.
The early atmosphere was dominated by carbon dioxide and water vapour from volcanic activity. Oxygen was not present in significant amounts until photosynthesis by early plants and algae began.
How did the oceans form on early Earth?
The early Earth was very hot, so water vapour remained as a gas. As the Earth gradually cooled, water vapour condensed and fell to the surface, accumulating to form the oceans.
How did CO₂ levels in the early atmosphere decrease as oceans formed?
Carbon dioxide is water-soluble and dissolved in large amounts into the new oceans. Carbonate substances were precipitated and formed sediments on the ocean floor. This process significantly reduced the amount of CO₂ in the atmosphere.
Volcanic eruptions released large amounts of ________ and water ________, plus ________ and hydrogen, with possible small amounts of ammonia and methane.
Volcanic eruptions released large amounts of carbon dioxide and water vapour, plus nitrogen and hydrogen, with possible small amounts of ammonia and methane.
How did oxygen levels in the atmosphere increase over time?
Primitive algae and later plants began photosynthesising, absorbing carbon dioxide and releasing oxygen.
As plant life spread over billions of years, oxygen levels gradually increased, reaching today's ~20% around 200 million years ago.
Which organisms first caused oxygen levels in the atmosphere to rise, and when did they appear?
Algae first evolved approximately 2.7 billion years ago and began photosynthesising.
Over the following billion years, small green plants also appeared, further increasing oxygen levels. This allowed more complex life forms to evolve.
True or False?
Oxygen has always made up approximately 20% of the atmosphere.
False.
The early atmosphere contained little or no oxygen. Oxygen increased gradually through photosynthesis by algae and plants over billions of years. The atmosphere only reached its current composition (20% O₂) approximately 200 million years ago.
What is the balanced symbol equation for photosynthesis?
Plants and algae use light energy to convert carbon dioxide and water into glucose and oxygen:
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
This reaction was responsible for the long-term increase in atmospheric oxygen.
Primitive ________ and later ________ began photosynthesising, absorbing ________ from the atmosphere and releasing ________.
Primitive algae and later plants began photosynthesising, absorbing carbon dioxide from the atmosphere and releasing oxygen.
Give three ways that carbon dioxide levels decreased from the early atmosphere.
1. CO₂ dissolved in the oceans and carbonates precipitated, forming sedimentary rocks.
2. Photosynthesis by plants and algae absorbed CO₂ and released O₂.
3. Dead organisms became compressed over millions of years into fossil fuels, locking carbon away.
How did the newly formed oceans cause CO₂ levels to fall?
CO₂ is water-soluble and dissolved into the oceans in large amounts. Carbonate substances were then precipitated and accumulated as sediments, which over time formed sedimentary rocks. This removed CO₂ from the atmosphere permanently.
True or False?
Coal formed when carbon dioxide gas was compressed underground.
False.
Plants and algae absorbed CO₂ during photosynthesis, incorporating the carbon into their tissues. When these organisms died, their remains were compressed over millions of years to form fossil fuels. The carbon in coal came from living organisms, not directly from compressed CO₂ gas.
What happened to the carbon absorbed by animals that ate plants in the early Earth?
Animals incorporated carbon into their bones and shells. When these organisms died, their remains formed sedimentary rocks, permanently storing carbon. This was another route by which CO₂ was removed from the atmosphere.
Why is the step "carbonates precipitated" important when explaining how CO₂ decreased as oceans formed?
Simply stating "CO₂ dissolved in the oceans" often gains only one mark.
To access the second mark, you must state that carbonate substances were precipitated and formed sediments (or sedimentary rocks). This step shows the CO₂ was permanently removed, not just dissolved.
CO₂ levels decreased because it ________ in the oceans forming carbonate ________, was absorbed by plants during ________, and carbon was locked up in ________ fuels.
CO₂ levels decreased because it dissolved in the oceans forming carbonate sediments, was absorbed by plants during photosynthesis, and carbon was locked up in fossil fuels.

Gas	Approximate amount
Nitrogen
Oxygen
Carbon dioxide
Water vapour
Noble gases

Gas	Approximate amount
Nitrogen	80%
Oxygen	20%
Carbon dioxide	Small amounts (~0.04%)
Water vapour	Small amounts
Noble gases	Trace amounts

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