Atmosphere

Total: 143 marks — Investigation 1: 37 · Investigation 2: 37 · Investigation 3: 32 · Investigation 4: 37.

Investigation 1 — land versus sea

• Q1 (10): Mark against the listed criteria. A common loss is joining the points with straight ruled segments instead of smooth curves, and forgetting to mark when the lamp went off — without that line the graph cannot show heating and cooling as two phases.
• Q2 (4): Sand: 37.7 − 22.0 = 15.7 °C (1). Water: 25.5 − 22.0 = 3.5 °C (1). 15.7 ÷ 3.5 = about 4.5 times (2). Accept own-data answers with correct working.
• Q3 (3): Sand: 37.7 − 26.5 = 11.2 °C (1). Water: 25.5 − 24.3 = 1.2 °C (1). The water retained its heat far better (1).
• Q4 (4): Water has a much higher specific heat capacity than sand (1) — it needs much more energy to change its temperature by 1 °C (1). So the same energy from the lamp raised the water's temperature far less (1), and, having stored that energy, the water also gave it up slowly, while the sand lost its heat quickly (1).
• Q5 (5): Independent: the material — sand or water (1). Dependent: temperature (1). Controlled, any three (3): mass (200 g), starting temperature, distance from the lamp, lamp power, container type and size, thermometer depth, time intervals.
• Q6 (3): Bigger (1). Mixing spreads the sea's heat through a much larger mass of water, so the surface warms even less (1), while on land the heat is concentrated in a thin top layer that gets very hot and cools fast (1).
• Q7 (4): Gqeberha is next to the sea, which has a high SHC (1), so it warms slowly in summer and cools slowly in winter, staying at a fairly steady temperature (1). Air blowing in off the sea takes on that steadiness, damping the coast's seasonal swings (1). Graaff-Reinet is surrounded by land and rock, which heat and cool quickly, so its temperature swings much more (1). (Credit dry air or altitude as an additional point, but not as the main reason.)
• Q8 (4): By day the land heats faster than the sea (1), warming the air above it, which expands, becomes less dense and rises (1); cooler, denser air from over the sea moves in to replace it — the sea breeze (1). At night the land cools faster than the sea, so the air over the sea is now the warmer, and the flow reverses into a land breeze (1).

Investigation 2 — greenhouse gases

• Q9 (2): A testable prediction linking the two variables, e.g. "If air contains more carbon dioxide, then it will warm up more when heated by the same lamp." (2). One mark only if it does not name both variables.
• Q10 (5): Independent: the gas in the bottle — air or CO₂ (1). Dependent: the temperature inside the bottle (1). Controlled, any three (3): bottle size and type, distance from the lamp, volume of liquid in the bottom, starting temperature, time intervals, thermometer position.
• Q11 (8): Mark against the listed criteria.
• Q12 (3): A: 33.2 − 21.0 = 12.2 °C (1). B: 35.0 − 21.0 = 14.0 °C (1). Difference at 20 min: 35.0 − 33.2 = 1.8 °C (1).
• Q13 (3): Yes (1): the CO₂ bottle warmed faster throughout (1) and finished 1.8 °C warmer, having risen 14.0 °C against 12.2 °C (1). A strong answer notes that the difference is small, so repeats matter.
• Q14 (4): Incoming sunlight is mostly short-wave radiation, which passes through the atmosphere and warms the surface (1). The warm surface gives off long-wave (infrared) radiation (1). CO₂ absorbs long-wave radiation (1) and re-emits it in all directions, some back towards the surface, so less heat escapes to space and the surface warms (1).
• Q15 (6): Any three, each with a reason (2 each): (i) the bottle is sealed, so it warms mainly by trapping air and stopping convection — the real atmosphere is open and convects freely; (ii) the CO₂ concentration in bottle B is thousands of times higher than in real air; (iii) the lamp shines infrared directly onto the bottles, whereas in reality the long-wave radiation comes up from the surface; (iv) CO₂ differs from air in other ways too (it conducts heat less well and has a different heat capacity), so part of the difference may not be the greenhouse effect at all; (v) the bottle is centimetres across, the atmosphere many kilometres deep. Award the reason mark only if it says why the difference matters.
• Q16 (3): The atmosphere is many kilometres deep, so the long-wave radiation leaving the surface passes through an enormous number of CO₂ molecules on its way out (1); even 0.04% of that column is a very large total amount of gas (1); and CO₂ is very effective at absorbing long-wave radiation, so small increases measurably change how much heat escapes — the energy budget only needs to tip slightly (1).
• Q17 (3): Any three (1 each): repeat the investigation several times and average; swap the bottles' positions between runs; use several bottles of each type; use identical, calibrated thermometers or a data logger; run it longer; keep the room temperature and draughts constant.

Investigation 3 — draw the atmosphere

• Q18 (8): Mark against the listed criteria. Altitude must be on the vertical axis.
• Q19 (6): Tropopause at 15 km (2) · stratopause at 50 km (2) · mesopause at about 90 km (2). One mark for each name and one for each altitude. Accept the tropopause drawn anywhere from 15 to 20 km, since the temperature is constant across that span.
• Q20 (4): Troposphere 0–15 km · stratosphere 15–50 km · mesosphere 50–90 km · thermosphere above 90 km (1 each).
• Q21 (3): Ozone layer within the stratosphere, roughly 15–35 km (1). Weather and clouds in the troposphere (1). Jet streams at the tropopause, at the top of the troposphere (1).
• Q22 (3): Temperature change = 16 − (−60) = 76 °C (1), over 15 km (1). 76 ÷ 15 = about 5.1 °C per km (1).
• Q23 (2): Ozone in the stratosphere absorbs ultraviolet light from the sun (1), and the absorbed energy heats the surrounding air (1).
• Q24 (4): The few molecules in the thermosphere absorb the sun's most energetic radiation (X-rays and extreme UV), so they move very fast — high temperature (2). But there are so few molecules that very little heat would be transferred to an astronaut, so it would feel cold (2). No marks for "it is closer to the sun".
• Q25 (2): 1 013 ÷ 1 000 ≈ 1 mb (2). Note that this agrees with the booklet's statement that the thermosphere's pressure is below 1 mb.

Investigation 4 — read the evidence

• Q26 (8): Mark against the listed criteria. A y-axis from about 300 to 440 ppm with a break symbol is ideal; a y-axis from zero squashes the trend but is not wrong.
• Q27 (4): 1960–1970: (325.7 − 316.9) ÷ 10 = 0.88 ppm per year (2). 2015–2025: (427.4 − 401.0) ÷ 10 = 2.64 ppm per year (2).
• Q28 (2): The rate of increase is itself increasing — CO₂ is rising faster now, about three times faster than in the 1960s (2). "It is increasing" alone earns 0: the question asks about the rate.
• Q29 (3): Increase = 427.4 − 280 = 147.4 ppm (1). 147.4 ÷ 280 × 100 (1) = about 53% (1).
• Q30 (2): 2000 was 369.7 ppm; the value was closest to 360 ppm in 1995 (1). The booklet was probably written using an older or rounded figure (1).
• Q31 (4): Estimate for 1993 between about 357 and 359 ppm (1). Cape Point's 355.6 ppm is within about 2–3 ppm of it (1). Two stations 18 000 km apart, in different hemispheres, record almost the same value, so CO₂ is well mixed through the whole atmosphere (1) — it is not concentrated in a local "layer", and emissions anywhere affect the air everywhere (1). Credit the observation that the Southern Hemisphere reads very slightly lower because most emissions are in the north.
• Q32 (8): (a) evidence · (b) cause · (c) evidence · (d) cause · (e) neither — a different problem, caused by CFCs · (f) evidence · (g) cause · (h) evidence. (1 each)
• Q33 (6): Four distinct, correctly described pieces of evidence (4), e.g. rising global temperatures, warming oceans, shrinking ice sheets and glaciers, less snow cover, declining Arctic sea ice, rising sea levels, more extreme weather, ocean acidification. One South African example (1), e.g. Cape Point's rising CO₂ record, the 2015–2018 Western Cape drought. Explains how at least one of them shows warming rather than simply naming it (1). Do not credit causes presented as evidence.

Marking note. Four graphs carry 34 of the marks on this sheet, which is about right: drawing and reading graphs is the skill this topic's data most needs. Mark Q15 generously for genuine critical thinking — spotting that a sealed bottle warms partly by stopping convection, which is how a real glass greenhouse works and not how the atmosphere works, is exactly the kind of thinking a Grade 10 scientist should be rewarded for.