Earth has a lot of oxygen in the atmosphere where Mars and Venus have their oxygen locked up in carbon dioxide and in minerals. Please read this article about a time in Earth's history called the Great Oxygenation Event that led to mass extinction and then answer this question: What was responsible for introducing large amounts of oxygen to Earth's atmosphere?

Cyano-bacteria

Explanation:

The great oxidization event was a massive event in the history of the planet when the earth atmosphere and the shallow oceans experience a rise in oxygen approx about 2.4 billion years. And as per the geologic and molecular evidence support that the biological induced molecular oxygen started to accumulate in the air and this caused almost all life on earth to go extinct. As per the chronology the prokaryotic and then later by eukaryotic organisms in the ocean produced oxygen needs for life.

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