Gravity pulled the solar nebula into a spinning disk, and as it slowly collapsed, 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.

HL Tauri
Earth Imapct

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 to the Earth, slowly filling the oceans and creating the we live in today.

But on the ground, it would have been a very strange place.  A hostile atmosphere of ammonia, methane and carbon dioxide would have been impossible to breathe.