the birth of the earth

five billion years ago,there was no planet earth and no sun.but the universe was already in full swing and whole generations of stars had already used hydrogen to creat the atomic building blocks-carbon,oxygen,silicon and others-that would later make up the planets.in a spiral arm of what is now our galaxy,clouds of these atoms started to condense,pulled together either by gravity or by shock waves from exploding stars. as they contracted,they began to rotate,forming a swirling disk at the heart of which lay a small young star.and so the sun began its life. at the young sun warmed,it blew awind of energetic particles through the dusty disk,driving the remaining gases outwards to form the giant planets jupiter and saturn.other dust grains accumulated into