The biggest mystery to me is in regard to plant life. Plants require carbon dioxide to survive, yet our atmosphere consists of only 0.04% CO2. If plants had evolved, they would have found a way to create energy from oxygen or nitrogen instead.
And good luck doing much with nitrogen. You need to go review your chemistry.
Oh yes, and oxygen is a completely unworkable source for energy to build sugars. Chemosynthetic organisms that do not use carbon dioxide and light are dependant on other sources of energy such as carbon dioxide or methane and hydrogen sulfide or ammonia.
Also note that plants build sugars in photosynthesis only to consume them by aerobic catabolism.