To search for signs of alien life, we may have to look into Earth’s past. We don’t have the technology to directly detect plants or animals, much less microbes, on alien worlds, so we have to look for the ways that they might affect their planet’s atmosphere. But what should we be looking for? New simulations of the gases in ancient Earth’s atmosphere can give us a hint.
Searching for oxygen is a good way to look for life, as there are few