During those early boring billion-year stretches, oxygen levels were swinging back and forth, dependent on the health of the cyanobacteria that produced it:
When Earth first formed 4.5 billion years ago, the atmosphere contained almost no oxygen. But 2.43 billion years ago, something happened: Oxygen levels started rising, then falling, accompanied by massive changes in climate, including several glaciations that may have covered the entire globe in ice.
Chemical signatures locked in rocks that formed during this era had suggested that by 2.32 billion years ago, oxygen was a permanent feature of the planet’s atmosphere.
But a new study delving into the period after 2.32 billion years ago finds that oxygen levels were still yo-yoing back and forth until 2.22 billion years ago, when the planet finally reached a permanent tipping point. This new research, published in the journal Nature on March 29, extends the duration of what scientists call the Great Oxidation Event by 100 million years. It also may confirm the link between oxygenation and massive climate swings.Stephanie Pappas, “Earth nearly lost all its oxygen 2.3 billion years ago” at LiveScience
Of course, one outcome of a shorter period during which oxygen is stable enough for complex life is — the obvious one — that all that bewildering complexity of life had to just sort of fall into place in a shorter period of time. If that’s unlikely, it’s an argument for underlying design.
The paper is closed access.
Great Oxygenation Event: