The Earths Atmosphere

Question 1

What is the composition of different gases in the atmosphere like today

Answer 1

• 78% of the atmosphere today is made of nitrogen
• 21% of the atmosphere today is oxygen
• There are also small amounts of carbon dioxide, water vapour and argon

These gases have stayed constant for the last 200 million years

Question 2

Where did the gases that formed the atmosphere come from

Answer 2

• Scientists believe that during the first billion years of the earth there was intense volcanic activity
• These volcanoes released gases that formed the atmosphere

Question 3

How did oceans form in the atmosphere

Answer 3

• One of the gases released in the atmopshere by volcanoes was water vapour
• Oceans formed when water vapour condensed as the earth cooled

Question 4

What other gas did the early volcanoes release huge amounts of

Answer 4

• The early volcanoes also released huge amounts of carbon dioxide.
• During this early stage, the atmosphere consisted of lots of carbon dioxide and little oxygen

Question 5

What other gases did the early volcanoes release

Answer 5

• The early volcanoes also released small amounts of methane and ammonia into the atmosphere
• They also released nitrogen which gradually built up over time in the atmosphere because of its unreactive nature

Question 6

What are the differences between the composition of gases in the early atmosphere and today

Answer 6

• The early atmosphere contained large amounts of carbon dioxide but the atmosphere today contains smaller amounts
• The earths early atmosphere contained little oxygen but now it is 21% oxygen

Question 7

Why did levels of carbon dioxide fall

Answer 7

• Carbon dioxide levels fell because when the water vapour condensed to form oceans carbon dioxide dissolved into the oceans to form weak acids
• This weak acid reacted with minerals in the sea to form precipitates.Over time these formed sediments of carbonate rock on the sea bed

Question 8

What is another reason why carbon dioxide levels fell

Answer 8

• Carbon dioxide levels also fell because the carbon dioxide was used to make the shells of organisms such as mussles and used to make corals. These eventually formed limestone.
• Carbon dioxide levels fell because as photosynthesising algea developed and took in carbon dioxide.

Question 9

Why did oxygen levels rise in the atmosphere

Answer 9

• Oxygen levels rose because around 2.7 billion years ago photosynthetic algea developed in the oceans
• Photosynthesis produced oxygen which enetered the atmosphere
• Over the following billion years plants evolved , this increased the levels of oxygen in the atmosphere