What would they eat? Tardigrades on earth, for example, eat plants, bacteria, other tardigrades, etc. But all of those require functioning ecosystems (even extr

What would they eat? Tardigrades on earth, for example, eat plants, bacteria, other tardigrades, etc. But all of those require functioning ecosystems (even extreme ones). If you put a bunch of tardigrades (or anything) on a planet without a suitable ecosystem, they'll all just die or stay dormant (in the case of tardigrades). You gotta terraform the heck out of it first. On our planet we try to measure something called net primary productivity (https://en.wikipedia.org/wiki/Primary_production?wprov=sfla1 https://en.wikipedia.org/wiki/Primary_production?wprov=sfla1), which is basically a measure of how much energy can be made useful to lifeforms in a planet's food web. There are only a few processes we know of that can do this, such as plants and algae and other photosynthetic organisms turning sunlight into edible organic substances for other consumers to eat. Tube worms chemosynthesizing from ocean floor hot spring vents is another one. These species are called autotrophs ("self feeders") and they constitute the basis of the entire food web on Earth, as far as we know. https://en.wikipedia.org/wiki/Autotroph?wprov=sfla1 https://en.wikipedia.org/wiki/Autotroph?wprov=sfla1 Without a suitable ecosystem for autotrophs, there isn't enough biologically available energy for the heterotroph species (everything else, us included, that eats other species to survive). So as far as know, a planet has to have a suitable environment for autotrophy to evolve first (or for alien life to arrive on, eg through exobiogenesis). You can't just send a bunch of consumers there and expect much to happen. At most they'd eat each other and then all become extirpated (locally extinct). Sci fi of course has us terraforming planets to make them (Earth) life sustaining, but that usually starts with plants and algae and such too before introducing the heterotrophs and inevitable monsters.