I think that it could still be that, but with a focus on panspermia in general, not the specific case of Earth. For the specific case of Earth, wouldn't we want

I think that it could still be that, but with a focus on panspermia in general, not the specific case of Earth. For the specific case of Earth, wouldn't we want to instead be investigating the survivability of single-celled microbes? It seems like one could rather trivially dismiss the idea that earth was seeded with tardigrade-like organisms based on the fact that they're too evolutionarily advanced to account for six of the seven kingdoms of life we have on this planet.