Year 7 answers
Tier 1: recall and identify
- Igneous, sedimentary, metamorphic.
- From the cooling and solidification of molten rock (magma or lava).
- Sediment is deposited in layers, compacted and cemented together into rock.
- An existing rock is heated and/or pressed without melting, changing its minerals and texture.
- Igneous: granite or basalt. Sedimentary: sandstone or limestone. Metamorphic: slate or marble.
- Large crystals mean slow cooling (underground); small crystals mean rapid cooling (on the surface).
- Sedimentary rock. It forms at low temperatures that do not destroy plant or animal remains, and sediment often buries them before decay is complete.
- Sedimentary layers form from sediment settling (bedding). Metamorphic layers form from pressure alignment (foliation).
- Coal.
- Granite is hard, weather-resistant and takes a polish — durable and attractive for benchtops.
Tier 2: explain and reason
- Basalt forms from lava on the surface that cools in days or weeks — crystals have no time to grow large. Granite forms underground where magma cools over thousands of years, allowing large interlocking crystals.
- Coal forms from plant material compressed in layers over millions of years — a sedimentary process. It is not formed from molten rock.
- Likely contains calcium carbonate. Could be limestone (sedimentary) or marble (metamorphic version of limestone).
- The rock cycle is a loop, not a one-way path. Any rock type can transform into any other given the right conditions — including melting sedimentary back to igneous, or weathering igneous to sediment.
- The rock was once a marine sedimentary layer. Tectonic forces pushed the layer upwards as plates collided, eventually raising it to mountain heights. The fossil is evidence that the rock formed underwater.
- Metamorphism requires high temperature and/or pressure. These conditions exist at depth (buried by kilometres of rock) or near plate boundaries — not at the surface.
Tier 3: apply to a novel context
- Slate. It is a metamorphic rock that splits cleanly along flat planes (foliation), making it ideal for waterproof roofing tiles.
- Likely igneous (granite or similar) — visible interlocking crystals with no layering suggest slow cooling underground.
- Example: granite weathers → quartz grains → deposited in river → compacted as sandstone (sedimentary) → buried and metamorphosed to quartzite → deeper still, melted to magma → cools as granite again.
- m = mm. At mm/year: years. The sediment may have been deposited in a stable lake or ocean environment, possibly during a long period of steady erosion upstream.
Challenge
- Zircon is a very hard mineral that can survive multiple trips through the rock cycle. A crystal can be released when its parent rock weathers, then redeposited in a new rock. The crystal’s age is measured by radioactive decay and reflects when it first crystallised, not when its current rock formed.
- Without plate tectonics: weathering, erosion, deposition and compaction (sedimentary formation) still work because they depend on water, wind and gravity. Metamorphism largely stops — there would be no mountain-building or subduction, so pressure-heating of deep rock is minimal. Igneous activity would also be reduced; most volcanism is plate-boundary related.
- Both are carbon. Charcoal is light, crumbly carbon formed at the surface from burnt wood. Diamond forms km deep under immense pressure and heat, arranging carbon atoms into a hard, transparent crystal. The rock-cycle context — the depth, pressure and slow growth — turns the same element into vastly different materials.
- Fish fossils in the lower layer indicate an aquatic environment (lake or sea) at that time. Desert dune patterns above indicate later dry, windy conditions. The absence of mixing suggests a rapid environmental change. Order: water environment first, then drying, then desert conditions, all preserved in the sequence of layers.