Answer:
The appearance of free oxygen in the Earth's atmosphere led to the Great Oxidation Event. This was triggered by cyanobacteria producing oxygen which developed into multicellular forms as early as 2.3 billion years ago
Explanation:
To clarify what I said here are some questions to help!
How did oxygen first appear?
Whiffs in the air is how oxygen first appeared billions of years ago.
For the most part, scientists agree that oxygen, though lacking in the atmosphere, was likely brewing in the oceans as a byproduct of cyanobacterial photosynthesis as early as 3 billion years ago
When was oxygen found?
2.33 billion years ago
Since its first appearance 2.33 billion years ago, oxygen accumulated in high enough concentrations to have a weathering effect on rocks just 10 million years later.
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