4.5 billion years ago, our Solar System forms from the remains of the supernova explosion.The sun and a great disk of matter emerge—all the planets and other members of our solar system family. Here begins the story of what will become one blue-and-white pearl of a planet. Great Bombardment! Comets and meteorites pelt the Earth. Finally a Mars-sized body impacts the proto-Earth with such force that the whole mass becomes molten once more. The intruder plunges towards the centre of the Earth and the moon is born, popping out from the side opposite the impact. This also causes the Earth to tilt 23 degrees to the side thenceforth giving rise to the seasons of the year.