The Earth's surface is always changing. Some changes are slow and take a very long time. Others are fast and happen in minutes, hours or days.

Weathering breaks rock into smaller pieces. Water, wind, ice and plant roots can all cause weathering. For example, water can seep into a crack and freeze. Ice takes up more space than water, so it pushes the crack wider.

Erosion is when pieces of rock and soil are moved to a new place by water, wind, ice or gravity. When they are dropped somewhere else, this is called deposition. Over a long time, rivers can carve deep valleys, and wind can build sand dunes.

Volcanoes are openings in the Earth's surface where melted rock, ash and gas come out. Melted rock underground is called magma; when it reaches the surface it is called lava. Lava cools and hardens into new rock, and can build new land.

The Earth's outer layer is broken into huge, slowly moving pieces called plates. An earthquake is a sudden shaking of the ground, often caused when rocks deep underground suddenly move. Earthquakes can crack the ground and cause landslides.