Water is life, falling on the ground, percolating into it, into the cracks between the pavement. Water finds its way through layers of rock and can appear thousands of years later in a spring. Water covers two thirds of the world in oceans and seas. But it is only a thin coat. Most of the world is molten or an iron core, with a mantle of rock floating above. Volcanos erupt around the world, Hawaii is a chain of volcanic islands erupting like a chain of bubbles in the Pacific ocean.

Are there other ‘water worlds’? Maybe Europa, a moon of Jupiter, which is covered in ice, could have oceans of water under its frozen crust.