Question: what were the gasses that came together to form the earth

Tim Stephens answered on 29 Jun 2012:

After the big bang, there was a ‘soup’ of elementary particles (the kind of thing that people like Mike try to understand at CERN). These then formed into simple atoms of hydrogen. Gravity collected the Hydrogen together into lumps, which became stars. As the star burns, it squashes Hydrogen together to make gasses with bigger nuclei (Like Helium), and then other heavier elements.
Once the star has consumed all its Hydrogen and other gasses it explodes as a supernova. Over Billions of years, this process formed all the elements that came together to form the earth. It means that you are entirely made out of stardust!