Coaching Centre
The changing Earth review
A summary of the whole Changing Earth chapter, key words, and a mixed test covering the Earth's structure, plates, the three rock types, weathering and erosion, the rock cycle, minerals, mining, fossils and dating.
Use this page to check the whole chapter. Read the summary, make sure you can explain every key word, then do the test without looking back.
Chapter summary
| Topic | What you need to know |
|---|---|
| 6A Inside the Earth | Formed 4.54 billion years ago; layered while molten. Crust (oceanic 5–10 km, continental 25–70 km), mantle (solid, flows slowly), liquid outer core (magnetic field), solid inner core. Lithosphere = crust + rigid upper mantle; asthenosphere below. Evidence from P and S waves (Lehmann), density, meteorites. |
| 6B Moving plates | Wegener's continental drift; Gondwana; sea-floor spreading. Plates move 1–10 cm/yr, driven by internal heat (convection, slab pull). Divergent, convergent (subduction, fold mountains), transform boundaries. Australia: 7 cm/yr north, intraplate earthquakes, hot-spot volcanoes, Budj Bim. |
| 6C Igneous rocks | Magma underground, lava at surface. Intrusive (slow, large crystals: granite, gabbro) vs extrusive (fast, small crystals: basalt, rhyolite). Glass (obsidian); gas holes (pumice, scoria). |
| 6D Sedimentary and metamorphic | Deposition, compaction, cementation. Conglomerate, sandstone, shale (grain size); limestone, coal (living things); rock salt (evaporation). Fossils. Metamorphism by heat and pressure without melting: shale → slate → schist → gneiss; limestone → marble; sandstone → quartzite. Regional vs contact. |
| 6E Weathering, erosion, deposition | Physical (frost, heating/cooling, salt, abrasion), chemical (acids, oxidation, water), biological. Erosion by water, wind, ice, gravity. Deposition when the carrier slows; sorting by size. Meanders, deltas, sea stacks, Uluṟu. |
| 6F The rock cycle | Model linking the three rock types through crystallisation, weathering and erosion, deposition, compaction and cementation, metamorphism and melting. Powered by internal heat and the Sun; gravity throughout. Hutton and deep time. |
| 6G Rocks and minerals | Minerals: natural solids with definite composition and crystal structure; rocks are mixtures of minerals. Colour, lustre, streak, hardness (Mohs 1–10), cleavage/fracture, density, special properties. Identifying rocks by grains, layers and reactions. |
| 6H Mining | Ores; Australian resources (iron ore, lithium, gold, bauxite). Exploration: mapping, magnetic, gravity, seismic, geochemical surveys, drilling. Open-cut, underground, in-situ leaching. Processing. Careers across the sciences. Rehabilitation, recycling, cultural heritage. |
| 6I Fossils | Body, mould and cast, trace, amber, petrified. Need hard parts, rapid burial in fine sediment, no oxygen or scavengers, undisturbed rock; found in sedimentary rock. Australian sites: Pilbara, Ediacara, Canowindra, Gogo, Riversleigh, Winton. |
| 6J Dating | Relative: superposition, cross-cutting, unconformities, index fossils. Absolute: radiometric dating and half-life (C-14, K-40, U-238). Earth 4.54 billion years. Geological time scale and mass extinctions. |
Putting it together
One idea links this whole chapter: the Earth is constantly recycling its rock, slowly, over enormous spans of time. Heat from inside the Earth moves plates, melts rock and changes it; energy from the Sun drives the wind and water that wear rock down and carry it away; gravity lays the pieces down in layers. Every rock records part of this story. Its crystals show how fast it cooled, its grains show how far they travelled, its fossils show what lived then, and its radioactive atoms show when it formed. Reading that record lets us find the minerals our society depends on, understand earthquakes and volcanoes, and look back more than four billion years.
Key words
asthenosphere · cementation · cleavage · compaction · contact metamorphism · continental drift · convection current · convergent boundary · core · crust · crystal · deposition · divergent boundary · erosion · extrusive · foliation · fossil · Gondwana · half-life · hardness · igneous · index fossil · intrusive · lava · lithosphere · lustre · magma · mantle · metamorphic · mineral · Mohs scale · ore · palaeontologist · plate tectonics · radiometric dating · rehabilitation · relative dating · rock cycle · sediment · sedimentary · seismic wave · streak · subduction · superposition · tailings · trace fossil · transform boundary · unconformity · weathering
Test yourself
Which layer of the Earth produces its magnetic field?
Swirling liquid iron makes the field.
Where an ocean plate subducts under a continent you would expect
Like the Andes.
A rock has large interlocking crystals of quartz, feldspar and mica. It is
Large crystals mean slow cooling underground.
Marble forms from
Calcite recrystallises.
Which is physical weathering?
No new substance forms.
A mineral is scratched by a steel nail (5.5) but scratches copper (3.5). Its hardness is about
Between 3.5 and 5.5.
Fossils are most likely to form when an organism
Protection from scavengers and decay.
After two half-lives, the fraction of radioactive parent atoms left is
½ × ½.
Which survey detects dense rock such as an ore body?
Dense rock slightly increases gravity.
Complete the rock cycle.
Classify each rock.
The rigid outer shell of the Earth is the . Molten rock underground is . Breaking down rock where it is, is called . The colour of a mineral's powder is its . In undisturbed layers the oldest is at the bottom: the law of .
A cliff on the NSW coast shows, from bottom to top: shale containing fossil shells, sandstone, and a dark basalt dyke cutting up through both layers. Use your knowledge of rocks, the rock cycle and dating to describe the history of this cliff, from the formation of the oldest rock to the present day.
First, mud settled in calm water such as a lagoon or the sea floor, burying the shells of animals living there. As more sediment piled on top, the mud was compacted and cemented into shale, and the shells were fossilised. Later the environment changed, and sand was deposited on top, perhaps by a river or along a beach. This was also buried, compacted and cemented into sandstone. By the law of superposition, the shale is older than the sandstone above it.
After both layers had formed, magma rose through cracks in the rock and cooled quickly in the narrow crack to form fine-grained basalt. Because the dyke cuts across both layers, the principle of cross-cutting relationships shows it is younger than both.
Later, plate movements uplifted the rocks, and weathering and erosion by waves and rain wore away the rock above, exposing the cliff we see today. Radiometric dating of minerals in the basalt (for example with potassium–argon) could give the dyke's age in years, showing that the sedimentary layers must be at least that old, and the shell fossils could be compared with index fossils to work out roughly when the shale was deposited.