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The Atmosphere

Worksheet Overview

QUESTION 1 of 10

This activity is about the air around us; what it's like now, and what it was like in the past.

It would be really cool to find this out by going in a time machine, but they don't exist. Fortunately, scientists can use evidence and thinking to work out what the Earth's atmosphere was like in the past, and compare it with what we have now.

Earth's atmosphere today

This pie chart shows the composition of the atmosphere today;

About four-fifths of the gas in the atmosphere is nitrogen. About one-fifth is oxygen. There is a small amount (about 1 %) of argon, and a very small amount (about 0.04 %) of carbon dioxide. Although the proportion of carbon dioxide is tiny, there is still enough carbon dioxide to have important effects on the Earth's environment.

Earth's atmosphere in the past

The planet Venus is like the Earth in some ways, but its atmosphere is very different. The atmosphere on Venus is nearly all carbon dioxide, with a small amount of nitrogen. Scientists think that Earth's atmosphere when it first formed (about 4.6 billion years ago) was like this, with lots of carbon dioxide and water vapour which had escaped from volcanoes.

Gradually, the Earth cooled down. About 3.8 billion years ago, it got cool enough for water vapour in the atmosphere to condense and make liquid water, which collected in oceans. A lot of the original carbon dioxide went from the atmosphere to the oceans.

The next big change was the appearance of algae on planet Earth. Algae are small green plant-like organsims; you often see them floating on the top of ponds, like this;

Green plants gradually converted nearly all the carbon dioxide in the Earth's atmosphere to oxygen, by photosynthesis;

carbon dioxide + water → glucose + oxygen.

Some of the oxygen produced ended up in rocks (think things like iron oxide), but eventually oxygen gas collected in the atmosphere as well. That eventually gave us the atmosphere we have now.

That's basically the story. There are several things happening, and it's important to think about them in the right order, so let's summarise them in a table;

How long ago? What happened? How did this affect the atmosphere?
4.6 billion years ago Earth formed, volcanoes started erupting The atmosphere was full of carbon dioxide, with some water vapour 
3.8 billion years ago Earth cooled enough for liquid water to condense Water went from the atmosphere into oceans, some carbon dioxide dissolved in the oceans as well
2.7 billion years ago Algae appeared, and started to photosynthesise Carbon dioxide was removed from the atmosphere. Initially the oxygen produced mainly went into rocks.
2.2 billion years ago Rocks could take no more oxygen Oxygen levels in the atmosphere began to increase, until there was almost no carbon dioxide in the atmosphere.

That's the outline of the story. Scientists aren't exactly sure about the precise dates, or some of the details, but this outline is consistent with a lot of things we see around us. Without a time machine (and nobody knows how to make one of those), it's the best we can do.

 

What are the two commonest gases in the Earth's atmosphere today?

argon

carbon dioxide

nitrogen

oxygen

Match these gases with their percentages in the Earth's atmosphere today?

Column A

Column B

argon
1 %
carbon dioxide
78 %
nitrogen
0.04 %
oxygen
21 %

What is the main gas in the atmosphere of Venus today?

argon

carbon dioxide

nitrogen

oxygen

Why is it useful to know what the atmosphere on Venus is like?

We need to know in case we send people to Venus

It isn't useful to know; Venus tells us nothing about Earth

We think that Venus's atmosphere now is what Earth's atmosphere was like

How many billion years ago did oceans form on Earth?

How did the atmosphere change 3.8 billion years ago? Tick all the correct answers.

Oxygen appeared in the atmosphere.

Some carbon dioxide was removed from the atmosphere.

All carbon dioxide was removed from the atmosphere.

Nearly all water was removed from the atmosphere.

What type of organism began to convert carbon dioxide into oxygen?

What process do algae use to convert carbon dioxide into oxygen? Pick a name and a reaction equation.

Match up these dates with the changes which happened in the atmosphere.

Column A

Column B

4.6 billion years ago
oxygen levels in the atmosphere began to rise
3.8 billion years ago
carbon dioxide levels fell to near zero
2.7 billion years ago
water left the atmosphere, taking some carbon diox...
2.2 billion years ago
atmosphere filled up with carbon dioxide and water...

Algae started producing oxygen 2.7 billion years ago, but we only start seeing evidence of oxygen in the atmosphere 2.2. billion years ago. Why is this?

Our evidence is wrong.

Initially, algae only produced tiny amounts of oxygen.

Initially, the oxygen produced was absorbed by rocks.

  • Question 1

What are the two commonest gases in the Earth's atmosphere today?

CORRECT ANSWER
nitrogen
oxygen
EDDIE SAYS
The main gases in Earth's atmosphere are nitrogen and oxygen. The amount of carbon dioxide is worrying (because very small amounts of CO2 have big effects), but still very small.
  • Question 2

Match these gases with their percentages in the Earth's atmosphere today?

CORRECT ANSWER

Column A

Column B

argon
1 %
carbon dioxide
0.04 %
nitrogen
78 %
oxygen
21 %
EDDIE SAYS
It's good to remember the exact percentages for these four gases. There are other gases as well, but in very tiny amounts.
  • Question 3

What is the main gas in the atmosphere of Venus today?

CORRECT ANSWER
carbon dioxide
EDDIE SAYS
Venus's atmosphere is nearly all carbon dioxide. That's the main reason that the planet is so hot (about 460 °C). There is a small greenhouse effect on Earth, but a much stronger one on Venus.
  • Question 4

Why is it useful to know what the atmosphere on Venus is like?

CORRECT ANSWER
We think that Venus's atmosphere now is what Earth's atmosphere was like
EDDIE SAYS
Both Venus and Earth formed in the same way. The difference is that Venus seemed to get stuck with its original atmosphere, but the atmosphere on Earth changed over time. Scientists have some ideas why Venus got stuck and Earth didn't, but we're not sure. Maybe you will work it out!
  • Question 5

How many billion years ago did oceans form on Earth?

CORRECT ANSWER
3.8
EDDIE SAYS
It's strange to think, but for the first 800 million years or so, the entire Earth was hot and dry, with lots of volcanoes erupting. There was no water at the surface; it was all in clouds in the atmosphere.
  • Question 6

How did the atmosphere change 3.8 billion years ago? Tick all the correct answers.

CORRECT ANSWER
Some carbon dioxide was removed from the atmosphere.
Nearly all water was removed from the atmosphere.
EDDIE SAYS
Nearly all the water on Earth went from the atmosphere to the surface- though there were still clouds and rain like now. Some of the carbon dioxide ended up dissolved in the oceans.
  • Question 7

What type of organism began to convert carbon dioxide into oxygen?

CORRECT ANSWER
algae
EDDIE SAYS
Algae are very primitive organisms. The first ones to evolve (blue-green algae) are single celled, but the cells do not have a nucleus. That's why they aren't classified as plants, even though they do some of the same things.
  • Question 8

What process do algae use to convert carbon dioxide into oxygen? Pick a name and a reaction equation.

CORRECT ANSWER
EDDIE SAYS
There's an overlap with biology here. Algae were able to do photosynthesis, converting carbon dioxide + water into glucose + oxygen.
  • Question 9

Match up these dates with the changes which happened in the atmosphere.

CORRECT ANSWER

Column A

Column B

4.6 billion years ago
atmosphere filled up with carbon ...
3.8 billion years ago
water left the atmosphere, taking...
2.7 billion years ago
carbon dioxide levels fell to nea...
2.2 billion years ago
oxygen levels in the atmosphere b...
EDDIE SAYS
The sequence is much more important than the exact dates (though you should learn them if you can!). Find ways of memorising sequences like this which work for your brain; it might be a flow chart, or a sequence of cartoon images, or a mnemonic.
  • Question 10

Algae started producing oxygen 2.7 billion years ago, but we only start seeing evidence of oxygen in the atmosphere 2.2. billion years ago. Why is this?

CORRECT ANSWER
Initially, the oxygen produced was absorbed by rocks.
EDDIE SAYS
If we look at very ancient rocks, we can see how they changed from absorbing small amounts of oxygen to large amounts. Once the rocks at the surface were full of oxygen, oxygen gas started to collect in the atmosphere.
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