The composition and evolution of the Earth's atmosphere

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Question 3
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The table below shows the estimated percentages of gases in the atmosphere of an Earth-like planet, Exo-3, in its early stage and today.

Table of Atmosphere Composition

GasEstimated percentage (%) in the early atmospherePercentage (%) in the atmosphere today
Nitrogen3.5YYY
Oxygen0.118.4
Carbon dioxide94.01.2
Other gases2.41.4
a.

Calculate the value of YYY in the table.

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b.

Look at the graph below, which shows how the percentages of gases in Exo-3's atmosphere have changed over time since its formation:

Line graph showing the percentage of gas in the atmosphere of Exo-3 over the last 4000 million years. The x-axis is 'Millions of years ago' from 4000 to 0 with divisions every 500 million years (4000, 3500, 3000, 2500, 2000, 1500, 1000, 500, 0). The y-axis is 'Percentage (%) of gas' from 0 to 100, with grid lines every 10%. There are three curves: 1) Carbon dioxide (dotted line): starts at 94% at 4000 million years ago, drops to 20% at 2000 million years ago, and reaches 1.2% by 0. 2) Nitrogen (dashed line): starts at 3.5% at 4000 million years ago, rises to 79.0% by 2000 million years ago, and remains constant at 79.0% from 2000 million years ago to 0. 3) Oxygen (solid line): remains at 0.1% until 2500 million years ago, then starts to rise, crossing exactly 10% at 1500 million years ago, and leveling off to its modern value of 18.4% starting 500 million years ago.

Use the graph to answer the following: When did the percentage of nitrogen in the atmosphere become constant?

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c.

When was the percentage of oxygen in the atmosphere 10%?

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The composition and evolution of the Earth's atmosphere Questions

  1. GCSE
  2. /Chemistry
  3. /The composition and evolution of the Earth's atmosphere