The early atmosphere of the earth would consist of gases like nitrogen and carbon dioxide and about 2.5 billion years ago oxygen started to form and some of these gases would have been expelled by volcanoes and also the atmosphere would stay close to the surface of the earth due to gravity that held it there.
One can tell by looking at the titration curve of an acid and base whether the acid used is a strong acid or a weak acid. For a titration of a strong acid and a strong base, the pH at the equivalence point will be neutral, that is, pH 7. If the titration involves a weak acid and a strong base, the pH at the equivalence point will not be neutral, the solution will be basic at the equivalence point.
A conclusion is basically something over all you wrote. So basically what you can do for a conclusion is maybe write something about each paragraph(s) but make it short sorry if this is bad :(