Chemistry of the Atmosphere: Composition & Evolution of the Earth’s Atmosphere

Question 1

Describe the proportions of gases in the modern atmosphere.

Answer 1

• 78% nitrogen
• 21% oxygen
• > 1% carbon dioxide
• small quantities of water vapour and noble gases

Question 2

Approximately how old is the Earth?

Answer 2

4.6 billion years old

Question 3

Why can scientists not be certain about the early atmosphere?

Answer 3

There is no evidence as it was so long ago.

Question 4

What was the Earth like during the first billion years? What impact did this have on the atmosphere?

Answer 4

• there was intense volcanic activity
• these volcanoes released water vapour, large amounts of carbon dioxide, nitrogen, which gradually build up in the atmosphere, and small amounts of methane and ammonia

Question 5

Describe the composition of the Earth’s early atmosphere.

Answer 5

• mainly carbon dioxide
• small but increasing amounts of nitrogen

Question 6

What are the 3 main differences between the early atmosphere and the atmosphere of the Earth today?

Answer 6

• much more nitrogen in the today’s atmosphere
• much less carbon dioxide in today’s atmosphere
• much more oxygen in today’s atmosphere

Question 7

How were the oceans formed?

Answer 7

The water vapour condensed to form oceans.

Question 8

What effect did the formation of the sea have on the atmosphere?

Answer 8

• decreased water vapour
• decreased carbon dioxide

Question 9

How was the amount of carbon dioxide in the atmosphere decreased?

Answer 9

This carbon dioxide reacted with minerals in the sea to form carbon precipitates which, over time, formed sediments on the sea bed.

Marine animals evolved and their shells and skeletons contained some of these carbonates from the oceans.

Plants and algae evolved absorbed some of the carbon dioxide for photosynthesis.

Some carbon was locked up in fossil fuels and rocks.

Question 10

How were sediments formed?

Answer 10

When plankton, plants and other marine animals die, they fall to the seabed and are buried under layers of sediment.

Over millions of years, they become compressed and form sedimentary rocks, oil and gas.

Question 11

How did the amount of oxygen in the atmosphere increase?

Answer 11

Plants and algae evolved which photosynthesised.

Question 12

Which sedimentary rock is made form the shells and skulls of dead animals (calcium carbonate)?

Answer 12

limestone

Question 13

Which sedimentary rock is made from dead plants?

Answer 13

coal

Question 14

Which fossil fuels are made from dead plankton?

Answer 14

crude oil
natural gas (methane)

Question 15

What is the greenhouse effect?

Answer 15

Greenhouse gases in the atmosphere maintain temperature on Earth high enough to support life

Question 16

How does the greenhouse effect work?

Answer 16

Greenhouse gases allow short wavelength radiation from he sun to pass through the atmosphere to the Earth’s surface but absorb the outgoing long wavelength radiation from the Earth causing an increase in temperature>

Question 17

What are 3 greenhouse gases?

Answer 17

• water vapour
• carbon dioxide
• methane

Question 18

Why is the greenhouse effect necessary for life?

Answer 18

It’s a natural phenomenon which without, the Earth would be too cold for life to exist.