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 rocky lumps which bumped into each other,sometimes joining together.slowly, the remaining material was swept up into a few large planets. one of these was the beginnings of the earth.the new earth was a hot young planet,warmed by atoms spewed out by an earlier generation of stars and by its own gravity. it suffered heavy bombardment from large asteroids and comets which rained down upon it,melting its surface. one of these impacts was so large that it creat the moon.as iron-rich minerals were drawn towards its centre,the young earth started to accumulate a great core of molten iron. this core now makes up 35 per cent of the mass of the earth-the remainder is made up of less dense,silicate rocks.as it grew,the molten core churned around,generating electrical currents.these gave the planet its frist magnetic field,which acted as a shield protecting the earth from radiation from space.heat escaping from the core kept the surrounding mantle of silicate rock hot.although this was soild,it flowed slowly,rather as ice does in a glacier,carrying heat to the surface in convection currents.meanwhile,as the core continued to form,gases rose to the surface,contributing to the early atmosphere.what had been born was not a dead lump of rock,but a living,dynamic new planet.