Sediments — Sieve It, Pour It, Read It

Total: 176 marks — Investigation 1: 41 · Investigation 2: 41 · Investigation 3: 24 · Investigation 4: 34 · Investigation 5: 36.

Investigation 1 — sieve a beach

• Q1 (2): Damp grains stick together in clumps (1), so fine grains would be held back on the coarser sieves and the fractions would be wrong — and the water itself would add mass (1).
• Q2 (6): One calculation shown, e.g. 291 ÷ 500 × 100 = 58.2 % (1). A: 0.6 · 4.4 · 19.2 · 58.2 · 16.8 % (2). B: 12.2 · 17.6 · 20.4 · 19.4 · 29.4 % (2). Totals: A 496 g = 99.2 %; B 495 g = 99.0 % (1). Accept the learner's own correctly calculated results.
• Q3 (3): A lost 4 g (0.8 %) and B lost 5 g (1.0 %) (1). Any two: dust blew away while shaking; grains stuck in the mesh; grains spilled between sieves; the scale reads only to 1 g, so each reading is rounded (2).
• Q4 (5): Bars for all five classes for both samples, side by side (1); size classes in order along the x-axis, labelled (1); y-axis "% of initial mass" with an even scale (1); accurate bars (1); key and title (1).
• Q5 (2): A — medium sand, 0.25–0.5 mm (1). B — fine sand and finer, the pan, below 0.25 mm (1).
• Q6 (2): A is better sorted: 58.2 % in one class and over 75 % in two neighbouring classes (1). B is spread over all five classes, none above 30 % (1).
• Q7 (3): The booklet is describing water that drops its load all at once — a flood or a turbidity current — so every size settles together, unsorted (1). A beach is worked by waves at much the same energy every day for years: the backwash carries the fine grains away and the waves cannot carry the big pieces up the beach, so sand of one size is left (1). Sorting needs time and a steady energy level; a river mouth has sudden changes — floods, tides, calm spells — so it stays mixed (1).
• Q8 (3): (a) 0.125 mm (⅛ mm) (1). (b) Silt (below 0.0625 mm) and clay (below 0.0039 mm) are far finer than any kitchen mesh, and the grains clump together (1). They separate by settling speed instead: in still water silt settles in minutes to hours, clay over days, so they form separate layers (1).
• Q9 (3): Same mass, but the flat shell took 1.4 s and the pebble 0.4 s — 3.5 times as long (1). A flat particle meets more resistance from the water and rocks from side to side instead of falling straight (1). Clay particles are tiny flat discs, so they sink extremely slowly — the milky water took days to clear (1).
• Q10 (3): The smaller the grain, the longer it takes to settle — pebble 0.4 s, medium sand 5.8 s, clay several days (1). In moving water, fine grains stay suspended and are carried far; they settle only where water is calm for long enough — offshore, quiet bays, estuaries (1). Coarse grains drop out quickly, near their source, even in turbulent water (1).
• Q11 (5): Any five, in a sensible order: dry the sample completely so the grains do not stick (1); weigh it — the initial mass (1); pass it through a series of sieves, coarsest mesh first, each one finer, shaking each (1); weigh what each sieve catches, and what passes the finest (1); express each mass as a percentage of the initial mass (1); name each fraction by its Wentworth class, e.g. sand ¹/₁₆–2 mm (1).
• Q12 (4): Boulders · cobbles · pebbles · granules · very coarse sand · coarse sand · medium sand · fine sand · very fine sand · mud · silt and clay — all eleven in order (3; deduct 1 per error or omission). Boulders at least 256 mm; silt and clay less than 0.0039 mm (1).

Investigation 2 — an avalanche in a box

• Q13 (3): a: 20 ÷ (16.0 − 3.4) = 1.59 cm/s; b: 20 ÷ 9.1 = 2.20 cm/s; c: 20 ÷ 9.8 = 2.04 cm/s (1 each).
• Q14 (3): a and b: the steepness of the ramp (1). a and c: the amount of sediment in the slurry — its density (1). Controlled — any one: the same volume of slurry; the same soil; the same water depth; the same way of pouring; fresh clear water each run (1).
• Q15 (2): A steeper slope gives a faster current — 2.20 against 1.59 cm/s (1). More sediment, a denser slurry, gives a faster current — 2.04 against 1.59 cm/s (1).
• Q16 (2): Water carrying colour but no sediment simply mixed (1), so a turbidity current is driven by the extra density of the suspended sediment, which gravity pulls downslope — not by the pouring or the colour (1).
• Q17 (3): Each 5 cm took longer: 2.6, 2.9, 3.3, then 3.8 s (1). Any two reasons: sediment settles out, so the current becomes less dense; it mixes with the clear water above and is diluted; on the flat floor gravity no longer pulls it forward; friction with the floor (2).
• Q18 (5): A layer that thins away from the ramp (1); coarse at the bottom grading up to fine sand and mud on top (1); labels with thicknesses (1); named a graded bed (1); the coarse grains are heaviest and settle fastest, so they drop out of the slowing current first, and the finest last (1).
• Q19 (4): Ramp = the continental slope (1); slurry = the turbidity current — saturated sediment slumping from the shelf edge (1); flat floor = the abyssal plain (1); thick wedge at the foot = the continental rise (1).
• Q20 (4): Points plotted, including (0, 0) (1); axes labelled with units — time (h), distance (km) (1); sensible scales (1); a smooth curve that flattens (1).
• Q21 (4): 65 ÷ 0.98 = 66; 120 ÷ 2.07 = 58; 85 ÷ 1.85 = 46; 90 ÷ 2.70 = 33; 70 ÷ 2.70 = 26; 70 ÷ 2.98 = 23.5 km/h (3 for all six; 2 for four or five; 1 for two or three; accept ±1). Average: 500 ÷ 13.28 = 38 km/h (1).
• Q22 (3): Fastest at the start, about 66 km/h, then slowing steadily to about 23 km/h (1). Any two: the seabed flattens from the continental slope onto the abyssal plain; sediment settles out so the current becomes less dense; it spreads out and mixes with seawater; friction (2).
• Q23 (2): They broke at the same instant as the shock, so they were broken by the shaking and the slumping slope itself (1), not by a current travelling to them — there is no travel time to calculate a speed from (1).
• Q24 (4): Model: 2.20 cm/s = 0.022 m/s (1). Real: 66 km/h = 66 000 ÷ 3 600 = 18 m/s (1). About 800 times faster (1). Any one reason: the real current was hundreds of metres thick and carried well over a hundred cubic kilometres of sediment; it ran down a slope hundreds of kilometres long; it picked up more sediment as it eroded the seabed; the box water is only centimetres deep (1).
• Q25 (2): They were telegraph cables — the first transatlantic telephone cable was laid only in 1956 (1). It was not one line between London and New York: twelve cables linking North America and Europe were broken (1).

Investigation 3 — a Secchi tube

• Q26 (3): 8 g/L: 3.2 cm; 4 g/L: 6.3 cm; 2 g/L: 12.3 cm; 1 g/L: 25.0 cm (3 for all four; 2 for three; 1 for two).
• Q27 (4): Axes labelled with units (1); sensible scales (1); points accurate (1); a smooth curve that falls steeply, then levels off (1).
• Q28 (3): The more sediment, the shallower the disk disappears (1); each doubling of the concentration roughly halves the depth (1); depth × concentration ≈ 25 every time (25.6, 25.2, 24.6, 25.0) — the depth is inversely proportional to the concentration (1).
• Q29 (2): 25 ÷ 0.5 = about 50 cm (1). The bottle is only about 30 cm deep, so the disk could not disappear — the result is beyond the range of the apparatus, not "perfectly clear water" (1).
• Q30 (2): Repeats show whether readings agree, and a mean reduces the effect of one misjudged reading (1). The moment the disk "disappears" depends on the light and on the observer's eyes, so both must stay the same for a fair comparison (1).
• Q31 (3): Any two: phytoplankton (a bloom); dissolved brown colour from rivers; air bubbles or foam (2). In the kitchen test the water, the disk, the light and the observer stay the same and only the amount of sediment changes, so any change in depth is caused by the sediment (1).
• Q32 (4): Calm: 2.7 × 5.5 = 14.9 m (1). After the flood: 2.7 × 1.2 = 3.2 m (1). In the calm week 9 m lies inside the euphotic zone, so the seaweeds can photosynthesise (1); after the flood 9 m is far below it, so too little light reaches them (1).
• Q33 (3): Suspended sediment cuts the light — the Secchi depth falls as the concentration rises (1). The euphotic zone becomes shallower than the seaweed bed, so the seaweeds cannot make enough food (1). Over weeks they use up their stores and die, and the animals that feed and shelter in the bed go with them — the mud does not need to be poisonous to kill (1).

Investigation 4 — what mud does to living things

• Q34 (3): Clear: 22.6 − 20.0 = 2.6 °C (1). Muddy: 25.0 − 20.0 = 5.0 °C (1). Rates: about 0.87 and 1.67 °C per 10 min — the muddy jar warmed about twice as fast (1).
• Q35 (2): The suspended particles absorb the light instead of letting it pass through (1) and turn it into heat, which warms the water around them (1).
• Q36 (2): Any two: warmer water holds less dissolved oxygen; animals' metabolism speeds up so they need more oxygen; temperatures above an animal's tolerance stress or kill it; a warm surface layer stops mixing with the cold water below, so less oxygen reaches the bottom.
• Q37 (3): Clean water drained in the same time on every pour, 14–15 s (1). Muddy water drained more slowly every time, from 17 s to 72 s (1), because the particles are trapped in the filter's pores and build up into a layer that blocks the flow — the clogging accumulates (1).
• Q38 (4): (a) Particles lodge between the gill filaments and coat them in mud and mucus (1), so less water flows over the gills and less oxygen diffuses into the blood — gaseous exchange fails and the fish can suffocate; sharp grains also damage the thin gill surfaces (1). (b) A mussel pumps water through its gills to feed and to breathe (1); its gills clog with useless mud, so it spends energy clearing them or keeps its shell shut, getting less food and less oxygen — in heavy sediment it starves, suffocates or is buried (1).
• Q39 (1): Any one: water flows over a gill's surface rather than through pores; gills are living and make mucus to clear particles; a fish can swim away to clearer water; the filter exchanges no gases.
• Q40 (3): Photosynthesis releases oxygen (1), which collects in the air spaces inside the disc, so the disc becomes less dense than the water and floats (1). The control had no bicarbonate, so no carbon dioxide and no photosynthesis — and none floated, which shows the floating is caused by photosynthesis, not by the light or warmth alone (1).
• Q41 (5): Three lines on one set of axes (1); a key (1); axes labelled — time (min) and discs floating (1); sensible scales (1); accurate plotting (1).
• Q42 (3): Clear: about 8 min; 2 g/L: about 12 min; 8 g/L: not reached in 20 minutes (2 for all three; 1 for two). The muddier the water the light passes through, the slower the photosynthesis (1).
• Q43 (3): Independent: the amount of sediment in the screen jar — the light reaching the discs (1). Controlled — any two: the same number and size of discs; the same leaf; the same bicarbonate solution; the same lamp and distance; the same temperature; the same size of screen jar (2).
• Q44 (5): A paragraph; one mark each for any five: the water becomes turbid and the Secchi depth falls; less light reaches the reef, so seaweeds (and the algae in any corals) photosynthesise less; the euphotic zone may become shallower than the reef; suspended mud absorbs sunlight and warms the surface water, which then holds less oxygen; it clogs the gills of fish and the filters of mussels, sponges and other filter-feeders, which starve or suffocate; settling mud smothers and buries attached animals and seaweeds; over several weeks the harm spreads through the food web.

Investigation 5 — read a core

• Q45 (6): A column 24 cm tall (1); six layers at the right thicknesses — 4.2 cm, a thin line, 5.5 cm, 2.8 cm, 6.2 cm, 5.2 cm (2); each layer shaded differently, with layer 4 shown coarse at the base and fine at the top (1); a depth scale every 50 cm (1); each layer labelled (1).
• Q46 (4): Biogenous — layer 1 or 5, calcareous ooze of foraminifera shells (1). Lithogenous — layer 3 red clay, layer 2 volcanic ash, or the sand of layer 4 (1). Hydrogenous — the onion-ringed metal lumps in layer 6, manganese nodules precipitated from seawater (1). Cosmogenous — the tiny magnetic spheres in layer 6, from space dust (1).
• Q47 (4): Layer 4 (1). Any three: it is graded, coarse at the bottom and fine at the top; it has a sharp base that cuts into the layer below; it holds broken mussel and limpet shells, which live in shallow water, at 4 500 m — so the sediment came down from the shelf; it is coarse sand in the middle of fine deep-sea clay and ooze, which could never deliver grains that size (3).
• Q48 (4): Layer 4 (28 cm) was laid down in a few hours by one turbidity current, not over 28 000 years, so it is left out (1). 240 − 28 = 212 cm of slow sediment (1) × 1 000 years per cm = about 212 000 years (1). Explaining that 240 000 years would count the turbidite as slow sediment (1). (Leaving out the 1 cm ash layer as well — 211 000 years — is also correct.)
• Q49 (3): Its foraminifera live today only in cold polar water, so the sea here was much colder — an ice age (glacial period) (1). Top of layer 5: 126 − 28 = 98 cm ≈ 98 000 years; bottom: 188 − 28 = 160 cm ≈ 160 000 years (1). So roughly 100 000 to 160 000 years ago (1).
• Q50 (3): A dredge is dragged along the seabed and scoops up loose surface material (1). The layers are mixed and damaged, and exactly where each piece came from is not recorded (1). There would be no layer order and no depths, so nothing could be dated or interpreted; a corer brings the layers up in place, relative to each other (1).
• Q51 (3): (a) "Of or containing hydrogen" (1). (b) Here "hydro-" means water: hydrogenous sediment forms when dissolved minerals precipitate out of seawater; a manganese nodule is metal oxides with almost no hydrogen, so the definition points the wrong way (1). Better: sediment formed from minerals that precipitate directly out of seawater by chemical reactions (1).
• Q52 (3): It uses sound (sonar), not radar — radar uses radio waves, which hardly travel through seawater (1). Strong sound pulses are sent down; echoes return from the seabed and from each boundary between layers beneath it (1). Sound travels and reflects differently in sand, clay and rock, so the pattern of echoes shows the layers and what they are made of (1).
• Q53 (6): One mark per resource with a correct place, any six: sand and gravel for building (many countries); coal off Scotland; heavy-mineral sands (ilmenite, rutile, zircon) at Richards Bay; diamonds off Kleinzee and southern Namibia, washed from Kimberlite pipes by rivers as alluvial sediment; oil and gas off Angola; oil and gas off the Southern Cape (Mossel Bay); manganese nodules (with nickel, cobalt and copper) on the deep-ocean floor.

Marking note. Q48 is the question this sheet is built around: a learner who multiplies 240 by 1 000 has read the core as a clock that never stopped. Layer 4 is a whole graded bed laid down in an afternoon — the same deposit they made in a box in Investigation 2. In Q51, the booklet's definition is examinable, so a learner who writes it is not wrong in a definitions question; the mark in (b) is for seeing why it does not describe the sediment.