Changes to the Atmosphere 49 minutes 49 marks Page of 24
Q. The amount of carbon dioxide in the Earth s atmosphere has changed since the Earth was formed. The amount of carbon dioxide continues to change because of human activities. (a) Cement is produced when a mixture of calcium carbonate and clay is heated in a rotary kiln. The fuel mixture is a hydrocarbon and air. Hydrocarbons react with oxygen to produce carbon dioxide. Calcium carbonate decomposes to produce carbon dioxide. (i) Complete each chemical equation by writing the formula of the other product. Hydrocarbons and calcium carbonate contain locked up carbon dioxide. What is locked up carbon dioxide? Page 2 of 24
(b) Graph shows how the percentage of carbon dioxide in the atmosphere changed in the last 4500 million years. Use information from Graph to answer these questions. (i) Describe how the percentage of carbon dioxide has changed in the last 4500 million years. Give two reasons why the percentage of carbon dioxide has changed. Page 3 of 24
(c) Graph 2 shows how the percentage of carbon dioxide in the atmosphere changed in the last 250 years. Should we be concerned about this change in the percentage of carbon dioxide? Explain your answer............. (Tota 0 marks) Page 4 of 24
Q2. This is a diagram of the layered structure of the Earth. (a) Draw a line from each layer to the correct name of the layer. Layer Name core Layer A crust Layer B mantle Layer C nucleus (3) Page 5 of 24
(b) The Earth s early atmosphere was 96% carbon dioxide. The atmosphere of the Earth today is 0.04% carbon dioxide. The percentage of carbon dioxide in the Earth s atmosphere has changed. Give two reasons why. You should consider: the formation of surface water (oceans) the formation of sedimentary rocks (limestone)............. (Total 5 marks) Page 6 of 24
Q3. Scientists study the atmosphere on planets and moons in the Solar System to understand how the Earth s atmosphere may have evolved. Titan is the largest moon of Saturn. The table shows data about some substances in the atmosphere of Titan. Substance Melting point in C Boiling point in C Nitrogen 20 96 Methane 83 64 Argon 89 86 Hydrogen 259 253 Carbon monoxide 205 92 (a) There is no water on Titan. The average surface temperature on Titan is 79 C. Which of the substances in the table would form oceans on Titan? Explain your answer............. Page 7 of 24
(b) Amino acids are essential to life. In the 950s the Miller-Urey experiment showed that simple amino acids, such as glycine (NH 2 CH 2 COOH), could have been produced from the Earth s early atmosphere. The Miller-Urey experiment showed that simple amino acids could be produced by reactions between hydrocarbons, ammonia and water. Explain how the Miller-Urey experiment suggests that reactions between the substances in Titan s atmosphere could also produce simple amino acids............................... (4) (Total 6 marks) Page 8 of 24
Q4. (a) Scientists have suggested that: the Earth formed as a molten ball of rock and minerals the rock and minerals cooled slowly the surface of the Earth was covered by volcanoes the volcanoes released gases that formed the Earth s early atmosphere. The pie charts show the approximate percentages of gases in the Earth s early atmosphere and in the Earth s atmosphere today. (i) Explain what has happened to most of the water vapour in the Earth s early atmosphere. Give two reasons why the percentage of carbon dioxide in the Earth s early atmosphere decreased.... 2... Page 9 of 24
(b) Scientists have suggested that the Earth consists of a core, mantle and crust. A traditional theory is that the core is made of iron and nickel. A controversial theory is that the core is like a nuclear reactor made of the radioactive elements uranium and plutonium. (i) Why can scientists not prove which theory about the core is correct? () How can the controversial theory be used to explain why the Earth s tectonic plates move? (3) (Total 8 marks) Q5. There was little or no nitrogen in Earth s early atmosphere, but a gaseous compound of nitrogen was present in small amounts. (a) Name this gaseous compound.... () Page 0 of 24
(b) In 892, Lord Rayleigh compared nitrogen from the air with very pure nitrogen obtained from nitrogen compounds. The density of the nitrogen was: nitrogen from the air =.2572 grams per litre nitrogen from nitrogen compounds =.25 grams per litre. Rayleigh and Sir William Ramsay proved that atmospheric nitrogen was not pure but contained five other gases, which together made up about % of the Earth s atmosphere. The gases were argon (0.94 %) and traces of helium, neon, krypton and xenon. The five gases are similar in that they show no chemical reactions but have different physical properties, eg density, melting point, boiling point. (i) Suggest one reason why scientists did not find these five gases in the atmosphere at an earlier date....... () Give one way of separating the five gases from each other....... () (iii) From the information given in the question, which prediction can be safely made? Tick ( ) one box. Nitrogen makes up about 78 % of the atmosphere. Argon has a density greater than the density of nitrogen. Neon, krypton and xenon have a density lower than the density of nitrogen. Nitrogen from nitrogen compounds must contain a very light gas such as hydrogen. () (Total 4 marks) Page of 24
Q6. The graph shows changes in the percentage of oxygen in the Earth s atmosphere over the last thousand million years. (a) (i) The percentage of oxygen in the atmosphere changed between 700 million years ago and 300 million years ago. How many more times greater was the percentage of oxygen in the atmosphere 300 million years ago compared with 700 million years ago? Answer =... times greater () The percentage of oxygen in the atmosphere changed between 700 million years ago and 300 million years ago. Explain why. Page 2 of 24
(iii) Suggest an explanation for the change in the percentage of oxygen in the atmosphere between 300 and 250 million years ago. (b) One theory for the origin of life on Earth is the chemosynthesis theory. This theory states that life on Earth began when more and more complex organic molecules and structures were synthesised. After a long time, these molecules and structures became living organisms. Two scientists, Miller and Urey, used the apparatus below to investigate the development of life on Earth. The gases in the reaction chamber were water vapour, methane and hydrogen. Page 3 of 24
When electric sparks were produced in the reaction chamber a mixture of organic compounds was produced. These organic compounds can be combined to make proteins. Does the Miller Urey experiment support the chemosynthesis theory for the origin of life? Explain your answer............. (Total 7 marks) Q7. For 200 million years the proportions of the different gases in the atmosphere have been much the same as today. Over the past 50 years the amount of carbon dioxide in the atmosphere has increased from 0.03% to 0.04%. (a) Describe how carbon dioxide is released into the atmosphere: (i) by human and industrial activity;............ from carbonate rocks by geological activity............. Page 4 of 24
(b) Explain how the seas and oceans can decrease the amount of carbon dioxide in the atmosphere................... (3) (c) (i) Give one reason why the amount of carbon dioxide in the atmosphere is increasing gradually....... () Give one effect that increasing levels of carbon dioxide in the atmosphere may have on the environment....... () (Total 9 marks) Page 5 of 24
M. (a) (i) H 2 O must be formula CaO must be formula carbon dioxide from the air / (Earth s early) atmosphere it = carbon (dioxide) accept carbon dioxide from millions of years ago formed (sedimentary) rocks or fossil fuels ignore trapped / stored (b) (i) decreases rapidly at first it = carbon (dioxide) then slowly or levels off allow both marks if the description is correct using either rapidly or slowly allow correct use of figures for either marking point if no other mark awarded, allow CO 2 decreased for mark any two from: it = carbon (dioxide) accept photosynthesis used by plants dissolved in oceans locked up in fossil fuels or formed fossil fuels locked up in rocks or formed rocks 2 (c) (yes) it = percentage of carbon (dioxide) ignore yes or no because the percentage of carbon dioxide is increasing which causes global warming (to increase) allow (carbon dioxide) causes greenhouse effect/climate change Page 6 of 24
or (no) because the percentage of carbon dioxide is low () compared to millions of years ago () allow global warming can be caused by other factors (e.g. Sun / water vapour / methane) [0] M2. (a) A core B mantle C crust (b) any two from: carbon dioxide dissolves / absorbs in water / oceans allow reacts with water plants / algae photosynthesise / absorb / use carbon dioxide accept remains of plants / algae / marine organisms contain locked up carbon dioxide / carbon in the form of fossil fuels do not accept plants use carbon dioxide for respiration marine organisms use (dissolved) carbon dioxide to form their shells / skeletons or limestone was formed from the shells / skeletons of marine organisms accept carbon dioxide became locked up in sedimentary rocks / carbonates / limestone or precipitation or formation of insoluble carbonates 2 [5] M3. (a) methane because at the surface temperature of 79 C only methane has melted but has not boiled accept a correct explanation using the boiling points (and melting points) of the gases or methane is a liquid and all the others are gases (b) CH 4 is a hydrocarbon or methane / carbon monoxide contains carbon or carbon monoxide + hydrogen hydrocarbon Page 7 of 24
nitrogen and hydrogen are present in Titan s atmosphere or nitrogen + hydrogen ammonia carbon monoxide contains oxygen or carbon monoxide + hydrogen / methane water amino acids contain carbon, hydrogen, nitrogen + oxygen or amino acids can be made from (methane), hydrogen, carbon monoxide and nitrogen OR lightning / ultraviolet / electrical discharge / high energy needed for reaction [6] M4. (a) (i) it = water vapour condensed accept temperature went below 00 C / boiling point of water allow cooled to form liquid / water / rain do not accept evaporated formed the oceans / seas ignore rain accept (water vapour) cooled and formed the ocean / sea for 2 marks any two from: ignore oxygen / nitrogen increased ignore reference to volcanoes / respiration used by (green) plants / algae accept photosynthesis / plants give out oxygen changed into oxygen dissolved in oceans / seas accept (locked up) in shells / skeletons (of animals) (locked up) in carbonates / sedimentary rocks (locked up) in fossil fuels / named fossil fuel 2 (b) (i) cannot get to / reach / drill to / see the core accept the core is (too) far down (into the Earth) / do not know what happens under the crust / Earth s surface accept it is (too) hot / radioactive ignore lack of evidence unqualified Page 8 of 24
any three from: heat / energy released from radioactive decay / processes accept radioactivity / nuclear reactions (causing) convection currents in the mantle 3 [8] M5. (a) ammonia accept NH 3 (b) (i) because the gases are unreactive accept because the measuring equipment was not very precise by fractional distillation (iii) argon has a density greater than the density of nitrogen [4] M6. (a) (i) 2 (oxygen) produced by algae / plants during photosynthesis (iii) catastrophe / volcano / asteroid destroyed most algae / plants dependent on first marking point (b) gives some support since showed that organic compounds might have been formed in early atmosphere allow yes since it showed organic compounds formed Page 9 of 24
but no evidence of structures / living organisms [7] M7. (a) (i) burning / breathing / respiration / fuels / food for mark each 2. rock is heated / subducted (owtte) / close to magma / melted. rock is decomposed / carbon dioxide released through volcanoes for mark each 2 (b) carbon dioxide reacts / dissolves in sea-water / dissolves in rain water insoluble carbonates / calcium carbonate are / is formed carbon dioxide turned into shells / coral / limestone / chalk / sediments also soluble hydrogencarbonates (calcium / magnesium) are formed photosynthesis by plants any three for mark each 3 (c) (i) sea unable to absorb all the extra carbon dioxide being produced more trees being cut down / deforestation increased burning of fuels / more cars / more industry (not more people) any one for mark global warming / greenhouse effect or effects such as melting ice caps / rising sea levels / climatic change / more deserts (not changes to ozone layer) for one mark [9] Page 20 of 24
E. (a) (i) Although many completions of the chemical equations were correct, the question produced a wide variety of symbols and formulae. The question was very poorly answered, with many students failing to grasp the idea of locked up carbon dioxide. Most seemed to miss the main point and instead focused on how the carbon dioxide would be released after being locked up, that is, referring to carbon dioxide which would be released into the atmosphere when fuels are burned. (b) (i) The better students realised that the percentage decrease of carbon dioxide had slowed down in the last 4500 million years. Many students only gained the compensation mark for stating that levels of carbon dioxide had decreased. It was perhaps surprising that so many students read the graph as increasing levels of carbon dioxide, with some thinking that graph related to an increase of carbon dioxide in the future. A reasonable proportion of students described how the percentage of carbon dioxide has changed in the last 4500 million years, usually with reference to photosynthesis and carbon dioxide dissolving in oceans. However, many students still seem to think that respiration is the same as photosynthesis. Many students incorrectly related the percentage change of carbon dioxide to the present day with both increasing levels of carbon dioxide due to more transport and decreasing levels due to a lack of fossil fuels. (c) The correct explanation for the change in carbon dioxide levels in the last 250 years mostly related to the argument that increasing levels would increase global warming. Another correct argument used was that it is not a concern at the moment because the level of carbon dioxide is still relatively low. E2. (a) The majority of students achieved full marks for knowing that the core is at the centre of the Earth, the next layer is the mantle and the outside layer is the crust. (b) Very few students obtained both marks on this question. Most common correct answers stated that carbon dioxide dissolves in or is absorbed by water or that plants use carbon dioxide for photosynthesis. Many students answers were not credited because they used terms such as water takes in rather than water dissolves or that plants breathe or suck in carbon dioxide. Students often incorrectly referred to carbon dioxide being trapped in sedimentary rocks, rather than being locked up in sedimentary rocks. E3. (a) Many students stated that methane was the only substance that would form an ocean, but they struggled to explain why. Students found negative numbers difficult to interpret, with many thinking that methane s boiling point, 64 C, was the lowest one listed. In addition, students did not link both the melting point and the boiling point into the answer. (b) The responses were far too general, with so many students including information only from the stem of part (b). It seemed clear that many students did not understand what the question was asking, as they concentrated on the Miller-Urey experiment more than Titan s atmosphere. Three or four marks were very rare with the most common mark gained being that energy, usually lighning, is needed to produce amino acids. Page 2 of 24
E4. (a) (i) This part was poorly answered with very few candidates gaining even one mark. Often candidates assumed that the water vapour could be converted into a different gas, such as oxygen or nitrogen. Other candidates did not appreciate the time interval between the Earth s early atmosphere and the Earth s atmosphere today and thought that the water vaporised and disappeared at the high temperature (400 o C) on the Earth s surface. This part was poorly answered with very few candidates gaining both marks. By far the most common correct response was that plants use carbon dioxide and change it into oxygen, although several candidates stated that plants breathed in or sucked in carbon dioxide. Reduced volcanic activity was the most common incorrect answer. Again there was an unexplained change of carbon dioxide into a different gas, such as oxygen or nitrogen. Very few candidates knew that carbon dioxide dissolves in sea water. (b) (i) This question was well answered with a majority of candidates realising that the Earth s core is inaccessible. However, the lack of evidence comment with no explanation did not gain any credit. This question was poorly answered by candidates. A few candidates gained two marks for realising that the controversial theory involved convection currents in the mantle. Some candidates mentioned radioactive processes but many of these thought that these processes would cause nuclear explosions causing thetectonic plates to move. E6. (a) (i) Most students read the graph correctly, but only half of the students followed this up by doing a correct calculation. (iii) Many students referred to plants or to photosynthesis but relatively few connected the two. This was reflected in only a fifth of students gaining full marks. The vast majority of students ignored the time scale and answered either in terms of human effects eg deforestation. Others answered in terms of animals absorbing the oxygen. Answers involving catastrophes wiping out plants were rare. Less than a fifth of students were able to score at least one mark. (b) Many students gained credit by stating that the production of organic molecules supported the theory, but very few referred to the fact that no structures / organisms were formed. E7. In part (a)(i) the vast majority of candidates gained both marks for stating the carbon dioxide is released by the burning of fossil fuels. A number of candidates stated that carbon dioxide is released by respiration which gained them one mark but to gain the second mark a reference was required to the fuel involved in this process, food. Part (a) was less well answered with many candidates confusing geological activity with weathering or the effects or acid rain on carbonate rocks. Page 22 of 24
To gain the first mark some reference was required to the geological process acting upon the rock. It was hoped that the candidates would state the idea given in the syllabus that the rock is moved deep into the Earth but other answers such as the idea of the rock being heated were accepted. For the second mark it was hoped that candidates would state the idea given in the syllabus that the carbon dioxide is released via volcanoes but other answers such as the idea of the decomposition of the carbonate rock were accepted. Many vague references were made to volcanoes which could not be awarded marks. Some candidates thought that Earth movements exposed the carbonate rock to the air where the carbon in the rock would react with oxygen. In part (b) few gained the three marks for ideas directly from the syllabus that the seawater reacts with/dissolves the carbon dioxide and forms insoluble carbonates and soluble hydrogencarbonates. A variety of other responses were accepted including one given by many candidates that plants in the sea use carbon dioxide during photosynthesis. In general most candidates were able to gain some of the marks for this question. Part (c) was well answered. A number of candidates lost the mark in part (c)(i) because they simply repeated their answer to (a)(i), burning fossil fuels. To gain this mark there had to be some indication that more fossil fuels are being burned. The idea of global warming was well known in part (c) although a few candidates still confuse this with damage to the ozone layer. Page 23 of 24
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