Rocks are made of minerals. There are three main types of rock. Igneous rock forms when hot, melted rock cools and hardens (for example granite and basalt). Sedimentary rock forms when layers of sand, mud or shells are pressed and cemented together over a very long time (for example sandstone and limestone). Metamorphic rock forms when heat and pressure deep underground change one rock into a new rock (for example limestone changes into marble).

Soil covers much of the land. It is a mixture of tiny pieces of broken-down rock (sand, silt and clay), humus (rotting bits of dead plants and animals), air and water. Plants grow in soil.

Water on Earth keeps moving in the water cycle. Evaporation: the Sun warms water and it turns into water vapor, an invisible gas. Condensation: the water vapor rises, cools and turns into tiny drops of water that make clouds. Precipitation: the drops join together and fall as rain, hail or snow. Collection: the water runs into rivers, lakes, oceans and the ground — and the cycle starts again.