Illustration of the four stages of the development of the inner Solar System over a period of nearly five billion years. The top panel shows the earliest stage when the debris disc around the Sun was composed of gas and tiny particles, typically less than one millimetre across. At the second stage the particles have formed large clumps, roughly 100 kilometres across. These bodies in turn formed the rocky planets including the Earth, shown in the third panel down. Over the subsequent four billion years the surface of the Earth developed to what we know now under the influence of meteor bombardment that delivered volatile materials including water, and the evolution of life on its surface.