The Early Atmosphere

Question 1

What is first in the timeline (4.1 billion years ago) and what is the evidence for it?

Answer 1

there was little to no oxygen, large amounts of water vapour and CO₂

volcanoes release gas into the atmosphere

*the earliest known rocks are about 4.1 billion years old

they contain iron compounds that form if there is no oxygen around

*examples include iron pyrite, which is broken down in oxygen and can’t form in it

Question 2

What is second in the timeline?

Answer 2

there was lots of CO₂
small amounts of water vapour, nitrogen and ammonia

the Earth cools down and water vapour condenses to form oceans (by falling as rain)

Question 3

What is third in the timeline (3 billion years ago) and what is the evidence for it?

Answer 3

organisms (cyanobacteria/blue green algae) formed and started to produce oxygen/photosynthesise

they use carbon dioxide and water to make oxygen and glucose

• the oldests fossils date from over 3 billion years ago
• they are all examples of organisms that could photosynthesise.

Question 4

What is fourth in the timeline (2.4 billion years ago) and what is the evidence for it?

Answer 4

oxygen had started to collect in the atmosphere
oxygen builds up in the oceans

• the oldest rocks that contain any type of iron oxide are from about 2.4 billion years ago
• they contain an iron oxide (Fe₃O₄) that forms when there is a little oxygen available

Question 5

What is fifth in the timeline (1.8 billion years ago) and what is the evidence for it?

Answer 5

There was a lot of oxygen in the atmosphere/ oxygen builds up in the atmosphere

The oceans absorb CO₂, sea creatures use it to make shells (from calcium carbonate).

• rocks dating from about 1.8 billion years ago contain a type of iron oxide which forms when there is a lot of oxygen present
• the iron oxide (Fe₂O₃) contains a greater ratio of oxygen to iron than the iron oxides found in older rocks

Question 6

What is last in the timeline (today) and what is the evidence for it?

Answer 6

The atmosphere contains 21% oxygen, 0.04% carbon dioxide, 78% nitrogen.

• the concentration of different gases is monitored around the world using sophisticated instruments for analysis
• heating copper in a sealed gas syringe containing 100 cm³ of air reduces the volume of gas by 21 cm³ (the oxygen reacts with the copper)

Question 7

Describe what happens to carbon dioxide absorbed by the oceans.

Answer 7

Marine organisms used the carbon dioxide to form shells made from calcium carbonate (CaCO₃).

The shells eventually form limestone rocks.

The shells of dead marine organisms fall to the sea bed, and become part of the sediment.

The layers of sediment become squashed and form sedimentary rocks.

Question 8

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

Answer 8

carbon dioxide + water → glucose + oxygen

CO₂ + H₂O → C₆H₁₂O₆ + O₂

balanced:
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

Question 9

What were the gases in the early atmosphere produced by?

Answer 9

volcanic activity

Question 10

What were the gases in the early atmosphere?

Answer 10

• little/no oxygen
• a large amount of carbon dioxide
• water vapour
• small amounts of other gases (ammonia, nitrogen)

Question 11

What happened 4.5 billion years ago?

Answer 11

the Earth was formed

Question 12

Describe a simple test for hydrogen.

Answer 12

a lighted wooden splint ignites hydrogen with a pop

Question 13

Some rocks contain iron. Very old rocks do not contain iron oxides but later ones do.

Explain how these rocks provide evidence for changes to the Earths atmosphere.

Answer 13

The very old rocks are evidence that the early atmosphere contained little/no oxygen because they don’t contain iron oxides.

Later rocks do contain iron oxides, which is evidence that oxygen was released into the atmosphere and reacted with iron in the rocks.

Question 14

Describe a simple test for oxygen.

Answer 14

a glowing wooden splint relights in oxygen

Question 15

Describe a simple test for carbon dioxide.

Answer 15

limewater turns milky when in the prescence of carbon dioxide

Question 16

State how the formation of oceans was a cause of decreasing carbon dioxide levels.

Answer 16

carbon dioxide dissolved in the oceans

Question 17

Describe why the levels of oxygen in the atmosphere increased.

Answer 17

plants produced oxygen by photosynthesis

Question 18

Suggest a reason that explains why scientists cannot be certain about the Earth’s early atmosphere.

Answer 18

no measurements were made then/no humans were on Earth then

Question 19

Name the biological process that increases oxygen levels and reduces carbon dioxide levels in the atmosphere.

Answer 19

photosynthesis

Question 20

What geological feature of a planet’s surface can give out large amounts of hot gas?

Answer 20

volcano

Question 21

Name the physical process that describes changing a vapour into a liquid

Answer 21

condensation

Question 22

What type of reaction occurs when metal gains oxygen?

Answer 22

oxidisation

Question 23

What sort of rocks are formed from layers of deposited material?

Answer 23

sedimentary

Question 24

Describe how the burning of fossil fuels effects the composition of the atmosphere.

Answer 24

Carbon dioxide increases, oxygen decreases and water vapour increases.