Gases consist only of atoms belonging to the simplest elements.

It all started 14 billion years ago with an event we call The Big Bang,which resulted in a universe consisting of gas alone.There were no stars and no planets.The gas was made up only of atoms belonging to the simplest elements.It was about 75 percent hydrogen and almost all the rest was helium.No elements like carbon, oxygen or nitrogen existed.No iron, silver or gold.In some places, the density of this gas was slightly higher than in others. Due to gravity, those places attracted even more gas,which further strengthened the pull of gravity,which then drew more gas in, and so on.