Oxygen was generally absent from the earth's atmosphere during the early Archean era. The dominant gas in the atmosphere was Carbon dioxide.
Explanation:
The Archean era is the period on earth when life began to form, about 4.6 billion to 541 million years ago. The atmosphere then was mainly composed of carbon dioxide spewed by the numerous volcanic eruptions at the time and cellular respiration of then primordial organisms. The earth's atmosphere was hot due to the greenhouse effect of carbon dioxide.
Oxygen, if any, has a insignificant proportion of the atmosphere at the time. This is until the evolution of photosynthetic organisms that harnessed energy from the sun to make their own food. They evolved oxygen in the process of photosynthesis. The accumulation of oxygen in the atmosphere is called the Great Oxygenation Event that beginning about 2.4 billion years ago.
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