C13 - The Earth's Atmosphere

Question 1

Describe phase one of the formation of the Earth’s atmosphere

Answer 1

=> Volcanoes erupted - released lots of gases
=> Mainly carbon dioxide, virtually no oxygen (similar to atmospheres of Mars and Venus today)
=> Volcanic activity also released nitrogen - built up in atmos. over time - as well as water vapour and small amounts of methane and ammonia

Question 2

Name the five gases that scientists think were present in the early atmosphere

Answer 2

• Carbon dioxide
• Nitrogen
• Water vapour
• Methane
• Ammonia

Question 3

What is the balanced symbol equation for photosynthesis?

Answer 3

6CO(2) + 6H(2)O —> C(6)H(12)O(6) + 6O(2)

Question 4

State the approximate composition of the atmosphere today.

Answer 4

• Nitrogen: 80%
• Oxygen: 20%
• Other gases: >1% of the atmosphere

Question 5

Name three greenhouse gases.

Answer 5

• Methane
• Carbon dioxide
• Water Vapour

Question 6

Explain how the greenhouse effect works to keep the Earth warm.

Answer 6

=> Greenhouse gases don’t absorb incoming short wavelength radiation from sun
=> Do absorb long wavelength radiation that is reflected off Earth
=> Re-radiate it in all directions - including back towards Earth
=> This longwave radiation is thermal radiation - results in warming of surface of Earth

Question 7

State three ways in which human activity is leading to an increase in carbon dioxide in the atmosphere.

Answer 7

• Deforestation: less CO(2) removed from atmos.
• Burning fossil fuels: carbon ‘locked up’ in these is released back into Earth
• Agriculture: farm animals produce methane through digestive processes (e.g. cattle)
• Creating waste: more landfill sites/agricultural waste - more CO(2) and methane produced by decomposition of waste

Question 8

What is a carbon footprint?

Answer 8

Total amount of carbon dioxide and other greenhouse gases emitted over the full life cycle of a product, service or event.

Question 9

Explain why reducing carbon dioxide emissions can be a difficult issue.

Answer 9

• Saying it easy, doing it is difficult
• Still work to be done on technologies that remove CO(2) from atmos.
• Some changes will impact economic growth of communities (especially developing countries)
• hard to make international agreements - most countries won’t sacrifice economic development if others won’t
• Individuals don’t want to make changes to their lifestyles/ not enough education as to why changes are necessary and how to make them

Question 10

Describe how the following air pollutants are produced and their effect on the Earth:

a) Particulates
b) Carbon monoxide
c) Sulfur dioxide
d) Nitrogen oxides

Answer 10

• Particulates: burning hydrocarbons (e.g. diesel) - respiratory problems in humans & global dimming
• Carbon monoxide: incomplete combustion - toxic; stops blood carrying oxygen around body; colourless and odourless
• Sulfur dioxide: oxidation of sulfur impurities in fossil fuels - acid rain & respiratory problems in humans
• Nitrogen oxides: oxidation of nitrogen gas in air at high temps. in vehicle engines - acid rain & respiratory problems in humans

Question 11

Explain how acid rain forms.

Answer 11

=> Sulfur dioxide reacts with water in clouds to form dilute sulfuric acid
=> This then falls as acid rain
(the same process happens with nitrogen oxides into dilute nitric acid)

Question 12

Sate two problems caused by acid rain.

Answer 12

• Kills plants
• Damages buildings and statues
• Makes metal corrode
• Respiratory problems in humans

Question 13

Describe phase two of the formation of the Earth’s atmosphere.

Answer 13

=> Water vapour condensed and formed oceans
=> Carbon dioxide dissolved in the oceans
=> Reacted to form carbon precipitates that formed sediments on the seabed
=> Green plants/algae evolved and absorbed some carbon dioxide to photosynthesise
=> Marine animals evolved - shells and skeletons contained carbonates from the oceans

Question 14

Describe phase three of the formation of the Earth’s atmosphere.

Answer 14

=> Green plants/ algae produced oxygen during photo.

=> Oxygen levels increased - more complex life evolved (e.g. animals)

Question 15

Explain how fossil fuels are created.

Answer 15

=> Plants/plankton/marine animals die and fall to seabed - become buried under sediments
=> Become compressed and form sedimentary rocks, oil and gas - trapping carbon within them and reducing carbon levels in atmos.
=> Crude oil and natural gas formed from deposits of plankton - form reservoirs under seabed when trapped in rocks
=> Coal = sedimentary rock made from thick plant deposits
=> Limestone = sedimentary rock made of calcium carbonate deposits of shells and skeletons of marine organisms.