Gravity pulled the solar nebula into a spinning disk as it slowly collapsed, and small proto-planets began clearing circular passageways though the churning dust. Once pressure and temperature at the core became high enough to crush hydrogen atoms together, our sun abruptly ignited -- driving away the dark clouds and letting the first sunlight shine through our solar system.

A similar process may be taking place right now in this new image of HL Tauri, taken by ALMA (the Atacama Large Millimeter/submillimeter Array in northern Chile) revealing the delicate structure of the gas rings surrounding a baby star 460 light-years from Earth.

Heavy iron sank into the center of our world, releasing enough heat to melt the planet into a seething ball of lava. The thin crust of solid rock that floated on the surface was repeatedly beaten by massive meteor strikes. One impact came close to destroying the Earth -- splattering it into pieces that would settle together to create the moon.

Drop by drop, impacting comets and asteroids delivered water into oceans that hissed with steam. A hostile atmosphere of ammonia, methane and carbon dioxide would have been impossible to breathe.