Free HSC Year 11 Earth and Environmental Science Flashcard Review
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How did Earth’s core form?
When the young Earth was largely molten, dense iron and nickel sank towards the centre (differentiation) while lighter silicates rose.
Where did the early atmosphere and oceans come from?
Volcanic outgassing released water vapour, carbon dioxide and nitrogen; as the surface cooled, water vapour condensed and rain filled the ocean basins.
What does the S-wave shadow zone show?
S waves cannot travel through liquid, so their absence beyond about 103° from the earthquake shows the outer core is liquid.
Average thicknesses of continental and oceanic crust?
Continental crust is about 25–70 km thick (about 30–40 km under most continents); oceanic crust is about 5–10 km.
How is rock density measured in the density practical investigation?
Measure mass on a balance and volume by water displacement, then calculate ρ = m ÷ V in g/cm³.
Why are zircons useful for dating early Earth?
Zircon takes in uranium but excludes lead, and it resists weathering, so its uranium–lead ratio records its crystallisation age; Jack Hills zircons are about 4.4 billion years old.
Felsic versus mafic minerals?
Felsic minerals are silica-rich and light coloured and crystallise at lower temperatures; mafic minerals are Mg–Fe-rich, dark and crystallise at higher temperatures.
Which mineral property is more reliable than colour?
Streak, the colour of the mineral powder on an unglazed porcelain tile.
What are the main soil horizons?
O (organic matter), A (organic matter mixed with mineral material), E (pale leached layer, in some soils), B (accumulated clay and iron) and C (partly weathered parent material), above bedrock.
State the principle of cross-cutting relationships.
A fault or igneous intrusion is younger than any rock it cuts through.
A sample has 12.5% of its parent isotope left. How many half-lives have passed?
Three, because (½)³ = 0.125.
When is open-pit mining preferred to underground mining?
When a large, fairly regular ore body lies close to the surface, because digging a pit is generally cheaper than developing an underground mine.
Name five lines of evidence for plate tectonics.
Jigsaw fit of continental shelves, matching fossils, the ocean floor profile, sea floor age increasing away from ridges, and symmetrical magnetic reversal stripes.
Why is the fit of continental shelves better evidence than coastlines?
Coastlines change with sea level and erosion, whereas the shelf edge marks the true edge of continental crust, giving a closer fit.
What does Glossopteris show?
This Permian seed fern is found in South America, Africa, India, Antarctica and Australia, suggesting these continents were joined as Gondwana.
Why did scientists reject Wegener’s continental drift?
He could not give a convincing mechanism: he could not identify forces strong enough to move continents, and critics such as Harold Jeffreys argued that continents could not plough through the ocean floor.
What did Holmes contribute?
A mechanism: convection currents in the mantle, driven by radioactive heat, that could carry continents.
What did Hess propose in 1962?
Sea floor spreading: new ocean floor forms at ridges, moves sideways and is destroyed at trenches.
How did Vine and Matthews test sea floor spreading?
They explained symmetrical magnetic stripes as spreading crust recording field reversals, predicting stripe widths that match the reversal time scale.
What did the Glomar Challenger show?
Drill cores from across the Mid-Atlantic Ridge, dated by fossils and isotopes, showed that the sea floor becomes older with distance from the ridge, confirming sea floor spreading.