Module 8 · Answers
Answers & explanations
Section A — Easy
01
Crust, mantle, outer core, inner core.
02
~78% nitrogen, ~21% oxygen.
03
(a) Igneous (b) Sedimentary (c) Metamorphic (d) Metamorphic
04
Carbon dioxide and methane (also water vapour).
05
Weather is short-term — what's happening now or this week. Climate is the long-term average pattern over decades.
Section B — Medium
06
Underground, magma cools slowly, so atoms have time to arrange into large crystals. At the surface, lava cools quickly, giving small crystals.
07
1) Sand particles are eroded from rocks and washed downstream. 2) They settle in layers in lakes/seas. 3) Buried under more layers, the sand is compacted and cemented together over millions of years to form sandstone.
08
Photosynthesis: removes CO₂ from atmosphere. Respiration: adds CO₂. Combustion: adds CO₂. Decomposition: adds CO₂.
09
At plate boundaries, plates push, slide or pull apart. Stress builds and releases as earthquakes; magma can rise to form volcanoes.
10
Saves a lot of energy compared with extraction (electrolysis is energy-hungry). Conserves bauxite ore reserves. Reduces landfill / pollution.
Section C — Hard
11
Trees normally remove CO₂ from the air via photosynthesis — fewer trees means less is removed. Burning the wood releases the stored carbon as CO₂. Both effects increase atmospheric CO₂.
12
Any three: melting ice caps and rising sea levels; coastal flooding; more frequent extreme weather (heatwaves, storms, droughts); shifts in habitats causing species loss; reduced food crops in some regions.
13
A freshwater reptile can't cross a salt-water ocean. The simplest explanation is that South America and Africa were once joined as one continent and have since drifted apart — direct evidence for moving tectonic plates.
14
Limestone is largely calcium carbonate (CaCO₃) — carbon locked in rock for millions of years. When heated to make cement, the limestone decomposes and releases CO₂ back to the atmosphere — which is why the cement industry has a large carbon footprint.