Atmosphere

Question 1

describe the composition of gases in the earth’s atmosphere using percentages

Answer 1

• ~80% nitrogen
• ~20% oxygen
• <1% other gases such as carbon dioxide, water vapour and noble gases

Question 2

how did early intense volcanic activity helpform the early atmosphere and oceans?

Answer 2

• They released gases that made the early atmosphere very similar to the atmospheres of Mars and Venus today.
• These atmospheres have: a large amount of carbon dioxide,
  little or no oxygen and small amounts of other gases, such as ammonia and methane
• Volcanic activity also released water
  vapour, which condensed as the Earth cooled to form the oceans.
• Nitrogen was probably also released by volcanoes which gradually built up in the atmosphere because it is unreactive.

Question 3

why did carbon dioxide in the atmosphere change (decrease) as the oceans were formed?

Answer 3

• The formation of sedimentary rocks- as the oceans formed, carbon dioxide dissolved to form soluble carbonate compounds so its amount in the atmosphere decreased. Carbonate compounds were then precipitated as
  sedimentary rocks, eg limestone.
• Uptake by living organisms- Carbon dioxide was also absorbed from the oceans into photosynthetic algae and plants. Many of these organisms, and the simple organisms in the food chains that they supported were turned into fossil fuels, eg crude oil, coal and natural gas, which all contain carbon.
  1. Coal is a fossil fuel 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.
  2. Crude oil and natural gas were formed from simple plants and tiny animals which were living in oceans and lakes. These small organisms died and their remains sank to the bottom where they were buried under sediments. The lack of oxygen prevented oxidation from occurring. Over millions of years, heat and pressure turned the remains of the organisms into crude oil and natural gas. Natural gas contains the smallest molecules and is often found on top of crude oil, trapped under sedimentary rock.

Question 4

state the approximate time in earth’s history when algae evolved to start producing oxygen

Answer 4

approximately 2.7 billion years ago

Question 5

how did oxygen in the earth’s atmosphere increase and what were the effects of a gradually increasing oxygen level?

Answer 5

• Algae evolved to make their own food by photosynthesis
• Photosynthesis by primitive plants and algae released oxygen, which gradually built up in the atmosphere.
• Eventually, the amount of oxygen present in the atmosphere enabled animals to evolve.

Question 6

name 3 greenhouse gases

Answer 6

• water vapour
• carbon dioxide
• methane

Question 7

how do greenhouse gases causem an increase in earth’s temperature?

Answer 7

1. Electromagnetic radiation at most wavelengths passes through the Earth’s atmosphere.
2. The Earth absorbs most of the radiation and warms up.
3. The Earth radiates energy as infrared radiation.
4. Some of the infrared radiation goes into space.
5. Some of the infrared radiation is absorbed by greenhouse gases in the atmosphere.
6. The lower atmosphere warms up.

Question 8

what is the greenhouse effect and explain briefly how it works

Answer 8

• The retention of heat in the atmosphere caused by the build-up of greenhouse gases.
• greenhouse gases absorb heat radiated from the Earth then release energy in all directions, which keeps the Earth warm

Question 9

list 4 human activities that produce greenhouse gases

Answer 9

• farming cattle releases methane
• farming rice in paddy fields releases methane
• burning fossil fuels in vehicles and
  power stations releases carbon dioxide
• deforestation releases carbon dioxide and reduces the absorption of carbon dioxide through photosynthesis

Question 10

what 4 things should you consider when evaluating the quality of evidence on things like global warming?

Answer 10

• who did the research and whether they are trustworthy, skilled and experienced
• who funded the research, because that might cause some bias
• what methods were used to collect and analyse the data, because that might cause uncertainties in the evidence base
• which organisation is reporting or publishing the evidence

Question 11

3 arguments against the idea that human activity caused a rise in global warming

Answer 11

• caused by natural factors and cycles of climate change
• climate science is complicated and it is difficult to predict and explain what will happen to global temperatures in the future, so scientists cannot be certain about global warming
• media may sometimes present opinions and articles which are simplified, inaccurate, based on only some of the evidence or biased

Question 12

2 arguments for the idea that human activity caused a rise in global warming

Answer 12

• vast majority of scientists do believe that humans are responsible
• the majority of evidence in
  peer-reviewed journals supports the theory

Question 13

4 effects of global warming

Answer 13

• glaciers and polar ice melting
• sea levels rising
• patterns of rainfall changing, producing floods or droughts
• habitats changing

Question 14

define carbon footprint

Answer 14

the total amount of carbon dioxide (and other greenhouse gases) which are emitted over the full life cycle of a product, service or event.

Question 15

3 ways to reduce carbon footprint

Answer 15

• Maximise the efficiency of your energy use.
• Minimise your waste.
• Using renewable energy sources as an alternative to burning fossil fuels.

Question 16

what pollutant is produced from complete combustion of any fuel containing carbon atoms?

Answer 16

Carbon dioxide, CO2

Question 17

what pollutants are produced from incomplete combustion of any fuel containing carbon atoms?

Answer 17

Carbon monoxide, CO and Particulate carbon, C (soot)

Question 18

what pollutant is made from hydrocarbon fuel molecules which have not been oxidised at all?

Answer 18

Unburned hydrocarbons

Question 19

what pollutant is made from combustion of a fossil fuel which contains sulfur impurities?

Answer 19

Sulfur dioxide, SO2

Question 20

what pollutant is made from oxidation of atmospheric nitrogen inside the engine of a car, lorry, etc?

Answer 20

Nitrogen oxides, NOx

Question 21

what happens in the complete combustion of a hydrocarbon fuel?

Answer 21

• Complete combustion of a hydrocarbon fuel occurs when there is a good supply of oxygen.
• It releases the maximum amount of
  energy and produces carbon dioxide and water.
• To construct a symbol equation for the complete combustion of a hydrocarbon fuel, remember that the fuel reacts with O2 and the only products are CO2 and H2O.
• e.g. CH4 (methane) + 2O2 → CO2 + 2H2O

Question 22

what happens in the incomplete combustion of a hydrocarbon fuel?

Answer 22

• Incomplete combustion of a hydrocarbon fuel occurs when there is a poor supply of oxygen.
• Less energy is released.
• Water is still produced from the hydrogen atoms. Instead of carbon dioxide, you might get carbon monoxide or particulate carbon, known commonly as soot, or a mixture of both.
• To construct a symbol equation for the incomplete combustion of a fuel, you need to read the question to see whether carbon monoxide (CO) or carbon (C) is produced.
• e.g. 2C2H6 (ethane) + 5O2 → 4CO + 6H2O

Question 23

properties of carbon monoxide

Answer 23

• colourless
• odourless
• poisonous gas
• can cause death

Question 24

describe a problem caused by an increase of carbon monoxide in the air

Answer 24

Carbon monoxide can reduce the amount of oxygen that the body receives. A lack of oxygen means that the body can go into a coma, or even die.

Question 25

properties of sulfur dioxide

Answer 25

* dense colourless gas * soluble in water * has a suffocating and unpleasant smell of burnt matches

Question 26

describe a problem caused by too much sulfur dioxide in the atmosphere

Answer 26

it dissolves in rainwater to make acid rain which harms and kills plants and animals, especially those that live in aquatic environments. It can also damage man-made objects like statues and buildings.

Question 27

what is a particulate

Answer 27

* formed from the incomplete combustion of a hydrocarbon fuel * it is carbon monoxide or particulate carbon, known commonly as soot, or a mixture of both

Question 28

describe problems of too many particulates in the atmosphere

Answer 28

* can affect the atmosphere. When particulates are released during combustion, they can go into the atmosphere. Here, they can contribute to global dimming, as they prevent light from reaching Earth. This reduces photosynthesis. * Particulates can affect the body. The lungs in the human body can be affected by particulates. The particulates get trapped in the lungs and lead to respiratory problems.