SC21 - Earth and Atmospheric Science ✓

Question 1

SC21a - What was the likely composition of the earth’s early atmosphere?

Answer 1

Mainly carbon dioxide with small amounts of water vapour with little to no oxygen

Question 2

SC21a - What was likely responsible for the composition of the earth’s early atmosphere?

Answer 2

• There was lots of volcanic activity in the earth’s early years and so volcanoes probably were a a major part of it
• They release large amounts of carbon dioxide and water vapour and small amounts of other gases (inc. nitrogen)

Question 3

SC21a - What evidence supports ideas about earth’s early atmosphere?

Answer 3

• Other planets near to earth (i.e. Venus and Mars) are mainly made of carbon dioxide that is thought to be released form volcanoes
• These planets should have a similar atmosphere to what earth was like before humans affected it

Question 4

SC21a - Why may some scientists think earth’s atmosphere was made up of nitrogen mainly and why was this disregarded?

Answer 4

• Titan, a moon of Saturn is made of of >98% nitrogen
• However, unlike any other planets closer to earth, titan has an icy interior so is less likely to be similar to earth

Question 5

SC21a - How were the oceans formed?

Answer 5

The earth cooled down and the water vapour condensed forming oceans

Question 6

SC21a - What evidence supports the claim that the early atmosphere contained little to no oxygen?

Answer 6

• Volcanoes don’t produce oxygen
• Iron pyrite can’t form in the presence of oxygen and it can be found in very ancient rocks

Question 7

SC21a - How long ago did oxygen levels start to rise and how do we know this?

Answer 7

• About 2.4 billion years ago, iron oxide started to form. Oxygen had to be present for oxidation to occur
• There is fossil evidence of microorganisms that produced this
• Some geologists believe that only after enough oxygen was present to oxidise iron could atmospheric oxygen rise

Question 8

SC21b - Describe the changes in levels of oxygen and carbon dioxide in the earth’s atmosphere

Answer 8

Oxygen levels increased and carbon dioxide level decreased

Question 9

SC21b - In what three ways did oceans change the atmospheric composition?

Answer 9

• Water vapour lessened as it formed oceans
• Carbon dioxide dissolved in oceans reducing carbon dioxide in the atmosphere
• Sea creatures used the dissolved carbon dioxide to form shells made of calcium carbonate (limestone) allowing more carbon dioxide to dissolve

Question 10

SC21b - How did photosynthesis affect atmospheric composition?

Answer 10

Photosynthesis:

Carbon dioxide + Water -> Oxygen + Glucose

This reduced levels of carbon dioxide and increased levels of oxygen

Question 11

SC21b - How are stromalites formed and how does this show oxygen being produced?

Answer 11

• Cyanobacteria are photosynthetic organisms that produce a sticky mucus
• The mucus traps sand and the organisms need to move above it
• Eventually, these form stromalites
• As stromalites have been around for around 3 billion years this suggests that photosynthesis has been occurring for this long
• Oxygen has been produced by these organisms since then

Question 12

SC21b - What caused a second jump in the levels of atmospheric oxygen?

Answer 12

Cyanobacteria evolved forming land plants which photosynthesised increasing the levels of oxygen

Question 13

SC21b - What % of the atmosphere is oxygen?

Answer 13

21%

Question 14

SC21b - What is the test for oxygen?

Answer 14

In the presence of oxygen, a glowing splint will relight

Question 15

SC21c - Describe the greenhouse effect

Answer 15

• Energy from the sun is transferred to the earth by (shorter) infrared and light waves
• The earth absorbs some of this, warming up and then emits (longer) infrared waves
• Greenhouse gases in the atmosphere absorb the energy and re-emit it back to the earth
• This causes the temperature of the earth’s atmosphere to increase and is called the greenhouse effect

Question 16

SC21c - What are some greehouse gases?

Answer 16

• Carbon dioxide
• Methane
• Water Vapour

Question 17

SC21c - Why are greenhouse gases neccesary for our survivial?

Answer 17

Without them, the average temperature of the earth would be -18 degrees which is too cold.

Question 18

SC21c - What is/are the negative effects of the greenhouse effect?

Answer 18

It is believed that greenhosue gases leads to global warming and climate change causing avergae weather temperatures around the world to increase too much

Question 19

SC21c - What evidence may we have that greenhouse gases are responsible for global warming?

Answer 19

Since _~1850, the burning of fossil fuels (releasing carbon dioxide) for industry and so this inreased CO² levels. As this has increased, so has average global temperature and this suggests a strong correlation

Question 20

SC21c - What is a causal link and how must scientists show that it exists?

Answer 20

When one thing causes another. Scientists must collect evidence of why and how the correlation occurs.

Question 21

SC21c - How may scientists prove that CO2 causes temperatures to rise?

Answer 21

• In a lab, they can prove that CO2 absorbs infrared radiation.
• Satellite data can also show that with an increase in CO2, there is a decreasing amount of infrared radiation that leaves the earth’s atmosphere.
• This suggests that CO2 levels cause temperature to rise (causal link present)

Question 22

SC21d - How has human activity increased global warming?

Answer 22

• Burning fossil fuels releases CO2 which is a greenhouse gas
• Methane is a much more powerful greenhouse gas and is released when natural gas and oil are extracted
• Cattle have bacteria that produces methane during livestock farming
• Soil bacteria in landfill sites and paddy fields produces methane

Question 23

SC21d - What are the effects of climate change?

Answer 23

• Higher average temperature will cause ice to melt and sea levels to rise making flooding more common
• Some animals may migrate away from their habitats and may become extinct if they can’t adapt to new conditions - Weather will become more extreme as some areas become more wet and others become more dry
• More CO2 will dissolve into the ocean making it slightly more acidic. The change in pH can kill organisms

Question 24

SC21d - How can the impact of climate change be reduced and what are the drawbacks?

Answer 24

• Using renewable energy as they release little or no greenhouse gases. However this may not be enough
• Global engineering solutions such as reflecting sunlight or carbon capture. However some countries may not help and delicate ecosystems can be disrupted
• Helping locals to adapt to new conditions e.g. new irrigation systems and flood defenses how ever this can destroy natural habitats and may not work

Question 25

SC21b - What is the test for Carbon dioxide?

Answer 25

When Carbon dioxide is bubbled through limewater, it will cause it to turn from colourless to cloudy/milky