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I love this one. I really do. Quick Answer: I'd put the date at roughly 2.3 billion years ago, give or take. This is the date of the Great Oxygenation Event. It's when organisms (bacteria) began ...
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#1: Attribution notice removed
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System
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2020-06-01T14:13:40Z (over 4 years ago)
Source: https://worldbuilding.stackexchange.com/a/4157 License name: CC BY-SA 3.0 License URL: https://creativecommons.org/licenses/by-sa/3.0/