How To Use Proterozoic aeon In A Sentence

• The Proterozoic aeon (2,500-540 million years ago) saw episodic increases in atmospheric oxygen content.
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• The fossil record shows that the first eukaryotic life appeared on Earth at the beginning of the Proterozoic aeon, about two gigayears ago, when the Earth was only about half its present age. George’s Cosmic Treasure Hunt
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