The Earth: structure, rocks and the climate

Layers of the Earth

Crust (thin, solid rock), mantle (hot, slowly flowing rock), outer core (liquid iron and nickel) and inner core (solid, despite being hottest, because the pressure is enormous). That last point is a favourite question — the answer is pressure, not temperature.

Three kinds of rock

Igneous rock forms when molten rock cools; slow cooling underground gives large crystals, fast cooling at the surface gives small ones. Sedimentary rock forms when layers of sediment are compressed — it often contains fossils. Metamorphic rock forms when existing rock is changed by heat and pressure without melting.

The greenhouse effect and climate change

Some gases in the atmosphere — carbon dioxide, methane, water vapour — absorb heat radiated from the Earth and keep the planet warm enough to live on. Burning fossil fuels adds more carbon dioxide, so more heat is trapped and average temperatures rise. Note the wording: the greenhouse effect is natural and necessary; the problem is the enhanced effect.