A time traveler's survival guide. The vertical green bars are the only times in Earth's history with enough oxygen to breathe (hypoxia) and low enough to avoid oxygen toxicity (hyperoxia).

https://en.wikipedia.org/wiki/Hyperoxia

This was a screenshot I took months ago while watching a Geology Hub upload on YT. It was a lightbulb moment for my understanding of mass extinction events, (the largest was 250ma). I've referenced this multiple times, so thought I might share. Perhaps you find it as interesting as I do.