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Answer:
B) Oxygen
Explanation:
The atmosphere of Earth hadn't always had the compostion it has at present. When the atmosphere formed, ti was much different than what it is now, and that is due to certain codnitions that were present, but also due to certain conditions that were lacking.
The oxygen is a gas that is relatively abundant in the atmosphere at present, but in the distant past it was like that. The amount of oxygen in the Earth's atmosphere initially was very small, practically having no influence on anything.
This all started to change with the appearance of the first organisms on Earth. The first organism were producers. They were carbon based organisms that needed carbon dioxide in order to produce energy for themselves. A waste product from the process of photosynthesis, through which the energy was produced, was the oxygen. As more and more producers started to occupy the planet, more and more oxygen was pumped up into the atmosphere.
This led to significant changes on Earth. The oxygen made the oceans and the land much more suited for development of more complex organisms. The atmosphere cooled off because of the oxygen, thus the global temperatures became much more pleasant. Also, the oxygen started to contribute much more corrosion, as it has the ability to destroy the metals when they are exposed to it.
