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).
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.
even earth feels like an alien planet millions of years ago, imagine if advanced space faring civilization do probe earth and categorized it to be inhospitable before, during and after their civilization crumbled to dust.
We can just barely sometimes tell the difference between a small neptune, a large earth, an ocean planets, a coteless ocean planet, and a hycean planet. Trying to guage not just habitability but also terraformability is a ways off yet.
We can start with size and surface temperature though. We're not going to survive on a gas giant, and anything with a four digit temperature is right out.