Primordial atmosphere

The sun and its planets formed about 5 billion years ago following the explosion of a supernova, which is a big star, that before bursting had generated heavy elements starting from Hydrogen and Helium. At the beginning Earth was an enormous incandescent ball composed primarily of Hydrogen and Helium, but also by heavy elements such as carbon, nitrogen, oxygen, iron and silicon which had been flung into space by the explosion. After that, the planet cooled down and part of the lighter gasses , such as hydrogen and helium, bonded with heavier elements and part got lost in space. Actually Helium was practically totally lost because it is light and not very reactive with other compounds, while a part of hydrogen (the lightest element of all) reacted with other elements forming hydrogenated compounds such as methane (CH4), ammonia (NH3), hydrogen sulphide (H2S) and water (H2O). Thanks to gravity the heavier elements began to form a central nucleus, composed mainly of iron and nickel, surrounded by a mantle, formed by heavy elements and an outer crust, made of the lightest elements such as aluminium, potassium and sodium. While the crust was forming, many volatile gases coming from the center of the Earth were released through the cracks and created what we consider to be the primordial atmosphere. Indirect proof of the primordial atmosphere can be obtained from the mixture of gasses which are still being released nowadays by volcanoes and solfataras, whose composition is very similar to that of the primordial atmosphere.
Another proof of the primordial atmosphere composition theory is given by the atmosphere analysis of the farthest planets of the solar system thanks to a rover, and they have been found to be rich in hydrogen compounds.
The latest proof is obtained by analyzing meteorites which contain all of the assumed substances although in a very low concentration.
In any case scientists are sure that the primordial atmosphere contained no free oxygen (O2)and therefore ozone could not exist either (formed by three oxygen atoms O3, instead of two) and so the sun’s ultraviolet rays that generally are blocked by a thick ozone layer, could reach the planet’s surface in much larger quantities compared to today and help with their energy in the formation of primitive chemical compounds.

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