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Ever since its formation around 4.5 billion years ago, Earth's rotation been gradually slowing down, its days have gotten progressively longer as a result. Earth's slowdown not noticeable on human timescales, it's enough to work significant changes over eons. One changes is perhaps most significant of all, at least to us: lengthening the days are linked to oxygenation of Earth's atmosphere, a study from 2021. good work.

Specifically, the blue-green algae (or cyanobacteria) emerged about proliferated around 2.4 billion years ago have been able to produce more oxygen as a metabolic by-product because Earth's days grew longer. 
Check out the on the following video for summary on their research.

Earth's Rotation Is Slowing Down, And It Might Explain Why We Have Oxygen