Would you recognize life when you saw it? It might surprise you, but it isn't always obvious what's alive and what's not, or even how to define what it is to be alive! When we're looking for life on distant exoplanets it's even harder: we can't even get close enough to see it directly. So how do we find life on another world? Oddly enough it helps to start small. 90% of the biomass on Earth is microscopic, and that much tiny life can lead to big changes in a planet's atmosphere. See if you can determine if each image shows signs of life or not.