Answer:
oxygen : produced through photosynthesis
carbon dioxide : released by volcanoes
lighter gases : escaped into space
heavier gases : sank to the surface
Step-by-step explanation:
at the beginning of the formation of the earth the atmosphere of the earth was so different from our atmosphere now . The earth was just melting ball full of hydrogen and helium gases only , after it started to be cooler and more sold the volcanoes erupted and released carbon dioxide and water vapor and nitrogen. and a type of a small bacteria used the radiation or the light of the sun and process of photosynthesis and produce oxygen , also the radiation of the sun breaked the molecule of water which consist of H2O and give more free Oxygen and the hydrogen and light gases started to escape into space, and the heavier gases sank to the surface