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How did oxygen first enter earth's atmosphere?

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These microbes conduct photosynthesis: using sunshine, water and carbon dioxide to produce carbohydrates and, yes, oxygen. In fact, all the plants on Earth incorporate symbiotic cyanobacteria (known as chloroplasts) to do their photosynthesis for them down to this day. read more

Yet no one has come up with a rock-solid test to determine the precise oxygen content of the atmosphere at any given time from the geologic record. But one thing is clear—the origins of oxygen in Earth's atmosphere derive from one thing: life. read more

Exactly when the first life on Earth - the ancestors of modern bacteria - began is a subject of debate, but evidence suggests it could be as much as 3.5 billion years ago. Early bacterial life introduced oxygen to the atmosphere. read more

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