It’s easy to take water for granted on Earth. It surrounds us all the time – in the sea, in rivers and streams, in rain, in clouds even when it’s not raining and in frozen form as snow and ice in winter. But where did all this water come from? In its earliest days, Earth was extremely hot – maybe as high as 2,000 degrees Celsius – so there couldn’t have been any liquid water on the surface at that time. In fact, there are several scientific theories as to how our planet got its water.
Earth is often described as a ‘water planet’, which is a good description of the way it appears from space, with water, in liquid or frozen form, covering three-quarters of its surface. But if you delve a little deeper, it turns out this is only a superficial impression. Most of our planet is solid rock, with water making up just 0.05 per cent of its mass. Ironically, although Earth is the only place in the Solar System where water is easy to see
