What changes were necessary in earth’s atmosphere to allow complex organisms to evolve?

Explanation:

At the beginning, Earth's atmosphere was constituted by methane, ammonia, water vapour and neon. So, at that time, the absence of ozone and major quantity of oxygen didn't allow to create complex organisms.

work yay..other than that pretty good actually it hot though (≧▽≦)

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jefferson hoped to establish trade with the native american people of the west and find a water route to the pacific. jefferson also was fascinated by the prospect of what could be learned about the geography of the west, the lives and languages of the native americans, the plants and animals, the soil, the rocks, the weather, and how they differed from those in the east.