Earth, rocks and the atmosphere
Chemistry · Key Stage 3 · The School
Inside the Earth
Four layers: a thin rocky CRUST we live on, a hot semi-solid MANTLE that flows very slowly, a liquid OUTER CORE of iron and nickel, and a solid INNER CORE — solid despite being hotter, because the pressure is immense. The mantle's slow flow drags the crust's plates around, which is why earthquakes and volcanoes cluster along plate boundaries rather than scattering randomly.
The rock cycle
IGNEOUS rock forms when molten rock cools — quickly at the surface giving small crystals, slowly underground giving large ones. SEDIMENTARY rock forms when fragments settle in layers and are compacted and cemented, which is why fossils are found in it. METAMORPHIC rock forms when existing rock is changed by heat and pressure without melting. Weathering, erosion, burial and uplift move rock between all three — no rock type is an endpoint.
The air, and what we are doing to it
The atmosphere is roughly 78% nitrogen, 21% oxygen, and about 1% argon, with carbon dioxide under 0.05%. That last fraction matters far beyond its size: carbon dioxide absorbs heat radiating from the surface. Burning fossil fuels releases carbon that was locked underground for millions of years, raising that concentration and warming the climate. Recycling and reducing use matter because the Earth's resources are finite and extracting them costs energy too.
You are handed three rocks. One has visible layers with a shell in it — SEDIMENTARY, formed from settled particles, and the shell shows it was under water. One has large interlocking crystals — IGNEOUS, cooled slowly deep underground, since slow cooling grows big crystals. One has bands and splits into flat sheets — METAMORPHIC, changed by heat and pressure. Grain size and structure tell you how it formed.