Composition and evolution of Earth's atmosphere (9.1) (M)

Question 1

For how long have the proportions of different gases in the atmosphere have been much the same as they are today?

Answer 1

200 million years

Question 2

Approximately, what proportion of the Earth’s atmosphere is nitrogen?

Answer 2

80%

Question 3

Approximately, what proportion of the Earth’s atmosphere is oxygen?

Answer 3

20%

Question 4

3 needed

What are some smaller gases, other than oxygen and nitrogen, in the Earth’s atmosphere?

Answer 4

• carbon dioxide
• water vapour
• noble gases

Question 5

What has happened to theories about what was in the Earth’s early atmosphere and how the atmosphere was formed?

Answer 5

They have changed and developed over time

Question 6

When did the Earth’s atmosphere form?

Answer 6

4. 6 billion years ago
   * Evidence for the early atmosphere is limited because of this*

Question 7

Why is there little evidence for the Earth’s early atmosphere?

Answer 7

Atmosphere formed 4.6 billion years ago

No living organisms (especially humans) were alive/present - so evidence not taken at time

so we rely on theories (from evidence taken in only recent years e.g. mars/venus)

Question 8

What does one theory about the Earth’s atmosphere suggest?

Answer 8

That during the first billion years of the Earth’s existence there was intense volcanic activity that released gases that formed the early atmosphere and water vapour that condensed to form the oceans

Question 9

In this theory, what was Earth early’s atmosphere similar to initially?

Answer 9

At the start of this period the Earth’s atmosphere may have been like the atmospheres of Mars and Venus today, consisting of mainly carbon dioxide with little or no oxygen gas

Question 10

How did nitrogen build up in the Earth’s early atmosphere according to this theory?

Answer 10

Volcanoes also produced nitrogen which gradually built up in the atmosphere

Question 11

Describe the proportions of methane and ammonia according to this theory about the Earth’s early atmosphere?

Answer 11

there may have been small proportions of methane and ammonia

Question 12

According to this theory, how did the proportion of carbon dioxide (initially) reduce in the air?

Answer 12

When the oceans formed carbon dioxide dissolved in the water and carbonates were precipitated (e.g. limestone) producing sediments, reducing the amount of carbon dioxide in the atmosphere

(carbon ‘locked in’ rocks)

Question 13

What produced the oxygen that is now in the atmosphere and how?

Answer 13

Algae and plants produced the oxygen that is now in the atmosphere by photosynthesis

Question 14

What is the equation for photosynthesis? (word and symbol)

Answer 14

Question 15

When did algae first start producing oxygen?

Answer 15

about 2.7 billion years ago

and soon after this oxygen appeared in the atmosphere

Question 16

How did animals evolve due to oxygen in the atmosphere?

Answer 16

Over the next billion years (from algae first producing oxygen about 2.7bn years ago) plants evolved and the percentage of oxygen gradually increased to a level that enabled animals to evolve (and survive)

Question 17

How did algae and (primitive) plants decrease the percentage of carbon dioxide in the atmosphere?

Answer 17

by photosynthesis

Question 18

Other than algae/plant photosynthesising, how else did the proportion of carbon dioxide in the air reduce?

Answer 18

Carbon dioxide was also decreased by the formation of sedimentary rocks and fossil fuels that contain carbon

Question 19

Describe the formation of coal?

Answer 19

Coal is a fossil fuel (contain hydrogen and carbon) which was formed from trees which were in dense forests in low-lying wetland areas.

Flooding caused the wood from these forests to be buried in a way that prevented oxidation taking place.

Compression and heating over millions of years turned the wood into coal

Question 20

Describe the formation of crude oil/natural gas?

Answer 20

Crude oil/natural gas formed from remains of ancient plankton deposited in the muds on the seabed.

These remains were covered by sediments that became layers of rocks when compressed over millions of years

These are now trapped between the layers

(contains carbon) as is fossil fuel

Question 21

Titan’s atmosphere is made of 98.4% nitrogen and 1.4% methane, why can’t have living organisms evolved on Titan the same way as on Earth?

Answer 21

Little/no oxygen

so photosynthesis hasn’t occurred

so little carbon dioxide present or oxygen-using animals could not have evolved

Question 22

6 marker! - important

The percentages of carbon dioxide and oxygen have changed from the Earth’s early atmosphere to today. Explain the processes that led to these changes

Answer 22

changes
• carbon dioxide has decreased
• oxygen has increased
processes
• volcanic activity released water vapour
• the water vapour condensed to form oceans
• carbon dioxide dissolved in oceans
• carbonates produce sediments
• carbon locked up in sedimentary rocks
• algae and plants evolved / appeared
• algae / plants absorbed carbon dioxide
• by photosynthesis
• which also released oxygen
• carbon locked up in fossil fuels

Question 23

4 marker

How could reducing the amount of sulfur in fossil fuels reduce the erosion of limestone?

Answer 23

sulfur reacts with oxygen to form sulfur dioxide

so less sulfur dioxide emitted

so less acid rain

so less limestone reacts with acid rain