Question

How did Earth come to have an oxygen atmosphere?

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A. Oxygen was the primary gas originally in Earth's atmosphere.
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B. Volcanoes released oxygen into the atmosphere.
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C. Early organisms created oxygen from other gases in the
atmosphere.
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D. Precambrian rocks released oxygen into the atmosphere.

Answer 1

The Earth's oxygen atmosphere was not present in the early stages of the planet. Over time, oxygen accumulated in the atmosphere due to the evolution of photosynthetic organisms like cyanobacteria.

Step-by-step explanation:

The Earth's oxygen atmosphere was not present in the early stages of the planet. The original atmosphere likely consisted of gases such as ammonia, methane, water vapor, and carbon dioxide, but very little oxygen. Over time, the atmosphere started to accumulate oxygen due to the evolution of photosynthetic organisms like cyanobacteria. These organisms produced oxygen as a byproduct of photosynthesis, leading to the oxygenation of the atmosphere.

Answer 2

C. Early organisms created oxygen from other gases in the atmosphere.

The correct answer is C. Early organisms created oxygen from other gases in the atmosphere.

Earth's early atmosphere was primarily composed of gases like nitrogen, carbon dioxide, methane, water vapor, and traces of other gases. The presence of oxygen in the atmosphere is largely attributed to the evolution of photosynthetic organisms, particularly cyanobacteria, during the Precambrian period.

Photosynthesis is a process by which organisms, using sunlight as an energy source, convert carbon dioxide and water into organic compounds while releasing oxygen as a byproduct. Cyanobacteria were among the first organisms to evolve photosynthesis, and they began producing oxygen through this process around 2.7 billion years ago.

Over time, the oxygen produced by cyanobacteria and other photosynthetic organisms accumulated in Earth's atmosphere. This process significantly changed the composition of the atmosphere, leading to the development of an oxygen-rich environment. It took millions of years for the oxygen levels to reach a level sufficient to support complex multicellular life forms.

The other options listed are not accurate explanations for the development of an oxygen atmosphere on Earth. Oxygen being the primary gas originally in Earth's atmosphere (Option A) is incorrect. Volcanoes releasing oxygen into the atmosphere (Option B) is not a significant source of oxygen, as volcanic activity primarily releases gases like water vapor, carbon dioxide, and sulfur dioxide. Precambrian rocks releasing oxygen into the atmosphere (Option D) is also incorrect, as it is the activities of early organisms that contributed to the rise of atmospheric oxygen levels.